v4.19.13 snapshot.
diff --git a/fs/dcache.c b/fs/dcache.c
new file mode 100644
index 0000000..2e7e8d8
--- /dev/null
+++ b/fs/dcache.c
@@ -0,0 +1,3139 @@
+/*
+ * fs/dcache.c
+ *
+ * Complete reimplementation
+ * (C) 1997 Thomas Schoebel-Theuer,
+ * with heavy changes by Linus Torvalds
+ */
+
+/*
+ * Notes on the allocation strategy:
+ *
+ * The dcache is a master of the icache - whenever a dcache entry
+ * exists, the inode will always exist. "iput()" is done either when
+ * the dcache entry is deleted or garbage collected.
+ */
+
+#include <linux/ratelimit.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/fsnotify.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/hash.h>
+#include <linux/cache.h>
+#include <linux/export.h>
+#include <linux/security.h>
+#include <linux/seqlock.h>
+#include <linux/bootmem.h>
+#include <linux/bit_spinlock.h>
+#include <linux/rculist_bl.h>
+#include <linux/list_lru.h>
+#include "internal.h"
+#include "mount.h"
+
+/*
+ * Usage:
+ * dcache->d_inode->i_lock protects:
+ * - i_dentry, d_u.d_alias, d_inode of aliases
+ * dcache_hash_bucket lock protects:
+ * - the dcache hash table
+ * s_roots bl list spinlock protects:
+ * - the s_roots list (see __d_drop)
+ * dentry->d_sb->s_dentry_lru_lock protects:
+ * - the dcache lru lists and counters
+ * d_lock protects:
+ * - d_flags
+ * - d_name
+ * - d_lru
+ * - d_count
+ * - d_unhashed()
+ * - d_parent and d_subdirs
+ * - childrens' d_child and d_parent
+ * - d_u.d_alias, d_inode
+ *
+ * Ordering:
+ * dentry->d_inode->i_lock
+ * dentry->d_lock
+ * dentry->d_sb->s_dentry_lru_lock
+ * dcache_hash_bucket lock
+ * s_roots lock
+ *
+ * If there is an ancestor relationship:
+ * dentry->d_parent->...->d_parent->d_lock
+ * ...
+ * dentry->d_parent->d_lock
+ * dentry->d_lock
+ *
+ * If no ancestor relationship:
+ * arbitrary, since it's serialized on rename_lock
+ */
+int sysctl_vfs_cache_pressure __read_mostly = 100;
+EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
+
+__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
+
+EXPORT_SYMBOL(rename_lock);
+
+static struct kmem_cache *dentry_cache __read_mostly;
+
+const struct qstr empty_name = QSTR_INIT("", 0);
+EXPORT_SYMBOL(empty_name);
+const struct qstr slash_name = QSTR_INIT("/", 1);
+EXPORT_SYMBOL(slash_name);
+
+/*
+ * This is the single most critical data structure when it comes
+ * to the dcache: the hashtable for lookups. Somebody should try
+ * to make this good - I've just made it work.
+ *
+ * This hash-function tries to avoid losing too many bits of hash
+ * information, yet avoid using a prime hash-size or similar.
+ */
+
+static unsigned int d_hash_shift __read_mostly;
+
+static struct hlist_bl_head *dentry_hashtable __read_mostly;
+
+static inline struct hlist_bl_head *d_hash(unsigned int hash)
+{
+ return dentry_hashtable + (hash >> d_hash_shift);
+}
+
+#define IN_LOOKUP_SHIFT 10
+static struct hlist_bl_head in_lookup_hashtable[1 << IN_LOOKUP_SHIFT];
+
+static inline struct hlist_bl_head *in_lookup_hash(const struct dentry *parent,
+ unsigned int hash)
+{
+ hash += (unsigned long) parent / L1_CACHE_BYTES;
+ return in_lookup_hashtable + hash_32(hash, IN_LOOKUP_SHIFT);
+}
+
+
+/* Statistics gathering. */
+struct dentry_stat_t dentry_stat = {
+ .age_limit = 45,
+};
+
+static DEFINE_PER_CPU(long, nr_dentry);
+static DEFINE_PER_CPU(long, nr_dentry_unused);
+
+#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
+
+/*
+ * Here we resort to our own counters instead of using generic per-cpu counters
+ * for consistency with what the vfs inode code does. We are expected to harvest
+ * better code and performance by having our own specialized counters.
+ *
+ * Please note that the loop is done over all possible CPUs, not over all online
+ * CPUs. The reason for this is that we don't want to play games with CPUs going
+ * on and off. If one of them goes off, we will just keep their counters.
+ *
+ * glommer: See cffbc8a for details, and if you ever intend to change this,
+ * please update all vfs counters to match.
+ */
+static long get_nr_dentry(void)
+{
+ int i;
+ long sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(nr_dentry, i);
+ return sum < 0 ? 0 : sum;
+}
+
+static long get_nr_dentry_unused(void)
+{
+ int i;
+ long sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(nr_dentry_unused, i);
+ return sum < 0 ? 0 : sum;
+}
+
+int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ dentry_stat.nr_dentry = get_nr_dentry();
+ dentry_stat.nr_unused = get_nr_dentry_unused();
+ return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
+}
+#endif
+
+/*
+ * Compare 2 name strings, return 0 if they match, otherwise non-zero.
+ * The strings are both count bytes long, and count is non-zero.
+ */
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+
+#include <asm/word-at-a-time.h>
+/*
+ * NOTE! 'cs' and 'scount' come from a dentry, so it has a
+ * aligned allocation for this particular component. We don't
+ * strictly need the load_unaligned_zeropad() safety, but it
+ * doesn't hurt either.
+ *
+ * In contrast, 'ct' and 'tcount' can be from a pathname, and do
+ * need the careful unaligned handling.
+ */
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
+{
+ unsigned long a,b,mask;
+
+ for (;;) {
+ a = read_word_at_a_time(cs);
+ b = load_unaligned_zeropad(ct);
+ if (tcount < sizeof(unsigned long))
+ break;
+ if (unlikely(a != b))
+ return 1;
+ cs += sizeof(unsigned long);
+ ct += sizeof(unsigned long);
+ tcount -= sizeof(unsigned long);
+ if (!tcount)
+ return 0;
+ }
+ mask = bytemask_from_count(tcount);
+ return unlikely(!!((a ^ b) & mask));
+}
+
+#else
+
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
+{
+ do {
+ if (*cs != *ct)
+ return 1;
+ cs++;
+ ct++;
+ tcount--;
+ } while (tcount);
+ return 0;
+}
+
+#endif
+
+static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+{
+ /*
+ * Be careful about RCU walk racing with rename:
+ * use 'READ_ONCE' to fetch the name pointer.
+ *
+ * NOTE! Even if a rename will mean that the length
+ * was not loaded atomically, we don't care. The
+ * RCU walk will check the sequence count eventually,
+ * and catch it. And we won't overrun the buffer,
+ * because we're reading the name pointer atomically,
+ * and a dentry name is guaranteed to be properly
+ * terminated with a NUL byte.
+ *
+ * End result: even if 'len' is wrong, we'll exit
+ * early because the data cannot match (there can
+ * be no NUL in the ct/tcount data)
+ */
+ const unsigned char *cs = READ_ONCE(dentry->d_name.name);
+
+ return dentry_string_cmp(cs, ct, tcount);
+}
+
+struct external_name {
+ union {
+ atomic_t count;
+ struct rcu_head head;
+ } u;
+ unsigned char name[];
+};
+
+static inline struct external_name *external_name(struct dentry *dentry)
+{
+ return container_of(dentry->d_name.name, struct external_name, name[0]);
+}
+
+static void __d_free(struct rcu_head *head)
+{
+ struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
+
+ kmem_cache_free(dentry_cache, dentry);
+}
+
+static void __d_free_external_name(struct rcu_head *head)
+{
+ struct external_name *name = container_of(head, struct external_name,
+ u.head);
+
+ mod_node_page_state(page_pgdat(virt_to_page(name)),
+ NR_INDIRECTLY_RECLAIMABLE_BYTES,
+ -ksize(name));
+
+ kfree(name);
+}
+
+static void __d_free_external(struct rcu_head *head)
+{
+ struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
+
+ __d_free_external_name(&external_name(dentry)->u.head);
+
+ kmem_cache_free(dentry_cache, dentry);
+}
+
+static inline int dname_external(const struct dentry *dentry)
+{
+ return dentry->d_name.name != dentry->d_iname;
+}
+
+void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
+{
+ spin_lock(&dentry->d_lock);
+ if (unlikely(dname_external(dentry))) {
+ struct external_name *p = external_name(dentry);
+ atomic_inc(&p->u.count);
+ spin_unlock(&dentry->d_lock);
+ name->name = p->name;
+ } else {
+ memcpy(name->inline_name, dentry->d_iname,
+ dentry->d_name.len + 1);
+ spin_unlock(&dentry->d_lock);
+ name->name = name->inline_name;
+ }
+}
+EXPORT_SYMBOL(take_dentry_name_snapshot);
+
+void release_dentry_name_snapshot(struct name_snapshot *name)
+{
+ if (unlikely(name->name != name->inline_name)) {
+ struct external_name *p;
+ p = container_of(name->name, struct external_name, name[0]);
+ if (unlikely(atomic_dec_and_test(&p->u.count)))
+ call_rcu(&p->u.head, __d_free_external_name);
+ }
+}
+EXPORT_SYMBOL(release_dentry_name_snapshot);
+
+static inline void __d_set_inode_and_type(struct dentry *dentry,
+ struct inode *inode,
+ unsigned type_flags)
+{
+ unsigned flags;
+
+ dentry->d_inode = inode;
+ flags = READ_ONCE(dentry->d_flags);
+ flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
+ flags |= type_flags;
+ WRITE_ONCE(dentry->d_flags, flags);
+}
+
+static inline void __d_clear_type_and_inode(struct dentry *dentry)
+{
+ unsigned flags = READ_ONCE(dentry->d_flags);
+
+ flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
+ WRITE_ONCE(dentry->d_flags, flags);
+ dentry->d_inode = NULL;
+}
+
+static void dentry_free(struct dentry *dentry)
+{
+ WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
+ if (unlikely(dname_external(dentry))) {
+ struct external_name *p = external_name(dentry);
+ if (likely(atomic_dec_and_test(&p->u.count))) {
+ call_rcu(&dentry->d_u.d_rcu, __d_free_external);
+ return;
+ }
+ }
+ /* if dentry was never visible to RCU, immediate free is OK */
+ if (!(dentry->d_flags & DCACHE_RCUACCESS))
+ __d_free(&dentry->d_u.d_rcu);
+ else
+ call_rcu(&dentry->d_u.d_rcu, __d_free);
+}
+
+/*
+ * Release the dentry's inode, using the filesystem
+ * d_iput() operation if defined.
+ */
+static void dentry_unlink_inode(struct dentry * dentry)
+ __releases(dentry->d_lock)
+ __releases(dentry->d_inode->i_lock)
+{
+ struct inode *inode = dentry->d_inode;
+
+ raw_write_seqcount_begin(&dentry->d_seq);
+ __d_clear_type_and_inode(dentry);
+ hlist_del_init(&dentry->d_u.d_alias);
+ raw_write_seqcount_end(&dentry->d_seq);
+ spin_unlock(&dentry->d_lock);
+ spin_unlock(&inode->i_lock);
+ if (!inode->i_nlink)
+ fsnotify_inoderemove(inode);
+ if (dentry->d_op && dentry->d_op->d_iput)
+ dentry->d_op->d_iput(dentry, inode);
+ else
+ iput(inode);
+}
+
+/*
+ * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
+ * is in use - which includes both the "real" per-superblock
+ * LRU list _and_ the DCACHE_SHRINK_LIST use.
+ *
+ * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
+ * on the shrink list (ie not on the superblock LRU list).
+ *
+ * The per-cpu "nr_dentry_unused" counters are updated with
+ * the DCACHE_LRU_LIST bit.
+ *
+ * These helper functions make sure we always follow the
+ * rules. d_lock must be held by the caller.
+ */
+#define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
+static void d_lru_add(struct dentry *dentry)
+{
+ D_FLAG_VERIFY(dentry, 0);
+ dentry->d_flags |= DCACHE_LRU_LIST;
+ this_cpu_inc(nr_dentry_unused);
+ WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
+}
+
+static void d_lru_del(struct dentry *dentry)
+{
+ D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+ dentry->d_flags &= ~DCACHE_LRU_LIST;
+ this_cpu_dec(nr_dentry_unused);
+ WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
+}
+
+static void d_shrink_del(struct dentry *dentry)
+{
+ D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
+ list_del_init(&dentry->d_lru);
+ dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
+ this_cpu_dec(nr_dentry_unused);
+}
+
+static void d_shrink_add(struct dentry *dentry, struct list_head *list)
+{
+ D_FLAG_VERIFY(dentry, 0);
+ list_add(&dentry->d_lru, list);
+ dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
+ this_cpu_inc(nr_dentry_unused);
+}
+
+/*
+ * These can only be called under the global LRU lock, ie during the
+ * callback for freeing the LRU list. "isolate" removes it from the
+ * LRU lists entirely, while shrink_move moves it to the indicated
+ * private list.
+ */
+static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
+{
+ D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+ dentry->d_flags &= ~DCACHE_LRU_LIST;
+ this_cpu_dec(nr_dentry_unused);
+ list_lru_isolate(lru, &dentry->d_lru);
+}
+
+static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
+ struct list_head *list)
+{
+ D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+ dentry->d_flags |= DCACHE_SHRINK_LIST;
+ list_lru_isolate_move(lru, &dentry->d_lru, list);
+}
+
+/**
+ * d_drop - drop a dentry
+ * @dentry: dentry to drop
+ *
+ * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
+ * be found through a VFS lookup any more. Note that this is different from
+ * deleting the dentry - d_delete will try to mark the dentry negative if
+ * possible, giving a successful _negative_ lookup, while d_drop will
+ * just make the cache lookup fail.
+ *
+ * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
+ * reason (NFS timeouts or autofs deletes).
+ *
+ * __d_drop requires dentry->d_lock
+ * ___d_drop doesn't mark dentry as "unhashed"
+ * (dentry->d_hash.pprev will be LIST_POISON2, not NULL).
+ */
+static void ___d_drop(struct dentry *dentry)
+{
+ struct hlist_bl_head *b;
+ /*
+ * Hashed dentries are normally on the dentry hashtable,
+ * with the exception of those newly allocated by
+ * d_obtain_root, which are always IS_ROOT:
+ */
+ if (unlikely(IS_ROOT(dentry)))
+ b = &dentry->d_sb->s_roots;
+ else
+ b = d_hash(dentry->d_name.hash);
+
+ hlist_bl_lock(b);
+ __hlist_bl_del(&dentry->d_hash);
+ hlist_bl_unlock(b);
+}
+
+void __d_drop(struct dentry *dentry)
+{
+ if (!d_unhashed(dentry)) {
+ ___d_drop(dentry);
+ dentry->d_hash.pprev = NULL;
+ write_seqcount_invalidate(&dentry->d_seq);
+ }
+}
+EXPORT_SYMBOL(__d_drop);
+
+void d_drop(struct dentry *dentry)
+{
+ spin_lock(&dentry->d_lock);
+ __d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
+}
+EXPORT_SYMBOL(d_drop);
+
+static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
+{
+ struct dentry *next;
+ /*
+ * Inform d_walk() and shrink_dentry_list() that we are no longer
+ * attached to the dentry tree
+ */
+ dentry->d_flags |= DCACHE_DENTRY_KILLED;
+ if (unlikely(list_empty(&dentry->d_child)))
+ return;
+ __list_del_entry(&dentry->d_child);
+ /*
+ * Cursors can move around the list of children. While we'd been
+ * a normal list member, it didn't matter - ->d_child.next would've
+ * been updated. However, from now on it won't be and for the
+ * things like d_walk() it might end up with a nasty surprise.
+ * Normally d_walk() doesn't care about cursors moving around -
+ * ->d_lock on parent prevents that and since a cursor has no children
+ * of its own, we get through it without ever unlocking the parent.
+ * There is one exception, though - if we ascend from a child that
+ * gets killed as soon as we unlock it, the next sibling is found
+ * using the value left in its ->d_child.next. And if _that_
+ * pointed to a cursor, and cursor got moved (e.g. by lseek())
+ * before d_walk() regains parent->d_lock, we'll end up skipping
+ * everything the cursor had been moved past.
+ *
+ * Solution: make sure that the pointer left behind in ->d_child.next
+ * points to something that won't be moving around. I.e. skip the
+ * cursors.
+ */
+ while (dentry->d_child.next != &parent->d_subdirs) {
+ next = list_entry(dentry->d_child.next, struct dentry, d_child);
+ if (likely(!(next->d_flags & DCACHE_DENTRY_CURSOR)))
+ break;
+ dentry->d_child.next = next->d_child.next;
+ }
+}
+
+static void __dentry_kill(struct dentry *dentry)
+{
+ struct dentry *parent = NULL;
+ bool can_free = true;
+ if (!IS_ROOT(dentry))
+ parent = dentry->d_parent;
+
+ /*
+ * The dentry is now unrecoverably dead to the world.
+ */
+ lockref_mark_dead(&dentry->d_lockref);
+
+ /*
+ * inform the fs via d_prune that this dentry is about to be
+ * unhashed and destroyed.
+ */
+ if (dentry->d_flags & DCACHE_OP_PRUNE)
+ dentry->d_op->d_prune(dentry);
+
+ if (dentry->d_flags & DCACHE_LRU_LIST) {
+ if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
+ d_lru_del(dentry);
+ }
+ /* if it was on the hash then remove it */
+ __d_drop(dentry);
+ dentry_unlist(dentry, parent);
+ if (parent)
+ spin_unlock(&parent->d_lock);
+ if (dentry->d_inode)
+ dentry_unlink_inode(dentry);
+ else
+ spin_unlock(&dentry->d_lock);
+ this_cpu_dec(nr_dentry);
+ if (dentry->d_op && dentry->d_op->d_release)
+ dentry->d_op->d_release(dentry);
+
+ spin_lock(&dentry->d_lock);
+ if (dentry->d_flags & DCACHE_SHRINK_LIST) {
+ dentry->d_flags |= DCACHE_MAY_FREE;
+ can_free = false;
+ }
+ spin_unlock(&dentry->d_lock);
+ if (likely(can_free))
+ dentry_free(dentry);
+ cond_resched();
+}
+
+static struct dentry *__lock_parent(struct dentry *dentry)
+{
+ struct dentry *parent;
+ rcu_read_lock();
+ spin_unlock(&dentry->d_lock);
+again:
+ parent = READ_ONCE(dentry->d_parent);
+ spin_lock(&parent->d_lock);
+ /*
+ * We can't blindly lock dentry until we are sure
+ * that we won't violate the locking order.
+ * Any changes of dentry->d_parent must have
+ * been done with parent->d_lock held, so
+ * spin_lock() above is enough of a barrier
+ * for checking if it's still our child.
+ */
+ if (unlikely(parent != dentry->d_parent)) {
+ spin_unlock(&parent->d_lock);
+ goto again;
+ }
+ rcu_read_unlock();
+ if (parent != dentry)
+ spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+ else
+ parent = NULL;
+ return parent;
+}
+
+static inline struct dentry *lock_parent(struct dentry *dentry)
+{
+ struct dentry *parent = dentry->d_parent;
+ if (IS_ROOT(dentry))
+ return NULL;
+ if (likely(spin_trylock(&parent->d_lock)))
+ return parent;
+ return __lock_parent(dentry);
+}
+
+static inline bool retain_dentry(struct dentry *dentry)
+{
+ WARN_ON(d_in_lookup(dentry));
+
+ /* Unreachable? Get rid of it */
+ if (unlikely(d_unhashed(dentry)))
+ return false;
+
+ if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
+ return false;
+
+ if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
+ if (dentry->d_op->d_delete(dentry))
+ return false;
+ }
+ /* retain; LRU fodder */
+ dentry->d_lockref.count--;
+ if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
+ d_lru_add(dentry);
+ else if (unlikely(!(dentry->d_flags & DCACHE_REFERENCED)))
+ dentry->d_flags |= DCACHE_REFERENCED;
+ return true;
+}
+
+/*
+ * Finish off a dentry we've decided to kill.
+ * dentry->d_lock must be held, returns with it unlocked.
+ * Returns dentry requiring refcount drop, or NULL if we're done.
+ */
+static struct dentry *dentry_kill(struct dentry *dentry)
+ __releases(dentry->d_lock)
+{
+ struct inode *inode = dentry->d_inode;
+ struct dentry *parent = NULL;
+
+ if (inode && unlikely(!spin_trylock(&inode->i_lock)))
+ goto slow_positive;
+
+ if (!IS_ROOT(dentry)) {
+ parent = dentry->d_parent;
+ if (unlikely(!spin_trylock(&parent->d_lock))) {
+ parent = __lock_parent(dentry);
+ if (likely(inode || !dentry->d_inode))
+ goto got_locks;
+ /* negative that became positive */
+ if (parent)
+ spin_unlock(&parent->d_lock);
+ inode = dentry->d_inode;
+ goto slow_positive;
+ }
+ }
+ __dentry_kill(dentry);
+ return parent;
+
+slow_positive:
+ spin_unlock(&dentry->d_lock);
+ spin_lock(&inode->i_lock);
+ spin_lock(&dentry->d_lock);
+ parent = lock_parent(dentry);
+got_locks:
+ if (unlikely(dentry->d_lockref.count != 1)) {
+ dentry->d_lockref.count--;
+ } else if (likely(!retain_dentry(dentry))) {
+ __dentry_kill(dentry);
+ return parent;
+ }
+ /* we are keeping it, after all */
+ if (inode)
+ spin_unlock(&inode->i_lock);
+ if (parent)
+ spin_unlock(&parent->d_lock);
+ spin_unlock(&dentry->d_lock);
+ return NULL;
+}
+
+/*
+ * Try to do a lockless dput(), and return whether that was successful.
+ *
+ * If unsuccessful, we return false, having already taken the dentry lock.
+ *
+ * The caller needs to hold the RCU read lock, so that the dentry is
+ * guaranteed to stay around even if the refcount goes down to zero!
+ */
+static inline bool fast_dput(struct dentry *dentry)
+{
+ int ret;
+ unsigned int d_flags;
+
+ /*
+ * If we have a d_op->d_delete() operation, we sould not
+ * let the dentry count go to zero, so use "put_or_lock".
+ */
+ if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
+ return lockref_put_or_lock(&dentry->d_lockref);
+
+ /*
+ * .. otherwise, we can try to just decrement the
+ * lockref optimistically.
+ */
+ ret = lockref_put_return(&dentry->d_lockref);
+
+ /*
+ * If the lockref_put_return() failed due to the lock being held
+ * by somebody else, the fast path has failed. We will need to
+ * get the lock, and then check the count again.
+ */
+ if (unlikely(ret < 0)) {
+ spin_lock(&dentry->d_lock);
+ if (dentry->d_lockref.count > 1) {
+ dentry->d_lockref.count--;
+ spin_unlock(&dentry->d_lock);
+ return true;
+ }
+ return false;
+ }
+
+ /*
+ * If we weren't the last ref, we're done.
+ */
+ if (ret)
+ return true;
+
+ /*
+ * Careful, careful. The reference count went down
+ * to zero, but we don't hold the dentry lock, so
+ * somebody else could get it again, and do another
+ * dput(), and we need to not race with that.
+ *
+ * However, there is a very special and common case
+ * where we don't care, because there is nothing to
+ * do: the dentry is still hashed, it does not have
+ * a 'delete' op, and it's referenced and already on
+ * the LRU list.
+ *
+ * NOTE! Since we aren't locked, these values are
+ * not "stable". However, it is sufficient that at
+ * some point after we dropped the reference the
+ * dentry was hashed and the flags had the proper
+ * value. Other dentry users may have re-gotten
+ * a reference to the dentry and change that, but
+ * our work is done - we can leave the dentry
+ * around with a zero refcount.
+ */
+ smp_rmb();
+ d_flags = READ_ONCE(dentry->d_flags);
+ d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED;
+
+ /* Nothing to do? Dropping the reference was all we needed? */
+ if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
+ return true;
+
+ /*
+ * Not the fast normal case? Get the lock. We've already decremented
+ * the refcount, but we'll need to re-check the situation after
+ * getting the lock.
+ */
+ spin_lock(&dentry->d_lock);
+
+ /*
+ * Did somebody else grab a reference to it in the meantime, and
+ * we're no longer the last user after all? Alternatively, somebody
+ * else could have killed it and marked it dead. Either way, we
+ * don't need to do anything else.
+ */
+ if (dentry->d_lockref.count) {
+ spin_unlock(&dentry->d_lock);
+ return true;
+ }
+
+ /*
+ * Re-get the reference we optimistically dropped. We hold the
+ * lock, and we just tested that it was zero, so we can just
+ * set it to 1.
+ */
+ dentry->d_lockref.count = 1;
+ return false;
+}
+
+
+/*
+ * This is dput
+ *
+ * This is complicated by the fact that we do not want to put
+ * dentries that are no longer on any hash chain on the unused
+ * list: we'd much rather just get rid of them immediately.
+ *
+ * However, that implies that we have to traverse the dentry
+ * tree upwards to the parents which might _also_ now be
+ * scheduled for deletion (it may have been only waiting for
+ * its last child to go away).
+ *
+ * This tail recursion is done by hand as we don't want to depend
+ * on the compiler to always get this right (gcc generally doesn't).
+ * Real recursion would eat up our stack space.
+ */
+
+/*
+ * dput - release a dentry
+ * @dentry: dentry to release
+ *
+ * Release a dentry. This will drop the usage count and if appropriate
+ * call the dentry unlink method as well as removing it from the queues and
+ * releasing its resources. If the parent dentries were scheduled for release
+ * they too may now get deleted.
+ */
+void dput(struct dentry *dentry)
+{
+ while (dentry) {
+ might_sleep();
+
+ rcu_read_lock();
+ if (likely(fast_dput(dentry))) {
+ rcu_read_unlock();
+ return;
+ }
+
+ /* Slow case: now with the dentry lock held */
+ rcu_read_unlock();
+
+ if (likely(retain_dentry(dentry))) {
+ spin_unlock(&dentry->d_lock);
+ return;
+ }
+
+ dentry = dentry_kill(dentry);
+ }
+}
+EXPORT_SYMBOL(dput);
+
+
+/* This must be called with d_lock held */
+static inline void __dget_dlock(struct dentry *dentry)
+{
+ dentry->d_lockref.count++;
+}
+
+static inline void __dget(struct dentry *dentry)
+{
+ lockref_get(&dentry->d_lockref);
+}
+
+struct dentry *dget_parent(struct dentry *dentry)
+{
+ int gotref;
+ struct dentry *ret;
+
+ /*
+ * Do optimistic parent lookup without any
+ * locking.
+ */
+ rcu_read_lock();
+ ret = READ_ONCE(dentry->d_parent);
+ gotref = lockref_get_not_zero(&ret->d_lockref);
+ rcu_read_unlock();
+ if (likely(gotref)) {
+ if (likely(ret == READ_ONCE(dentry->d_parent)))
+ return ret;
+ dput(ret);
+ }
+
+repeat:
+ /*
+ * Don't need rcu_dereference because we re-check it was correct under
+ * the lock.
+ */
+ rcu_read_lock();
+ ret = dentry->d_parent;
+ spin_lock(&ret->d_lock);
+ if (unlikely(ret != dentry->d_parent)) {
+ spin_unlock(&ret->d_lock);
+ rcu_read_unlock();
+ goto repeat;
+ }
+ rcu_read_unlock();
+ BUG_ON(!ret->d_lockref.count);
+ ret->d_lockref.count++;
+ spin_unlock(&ret->d_lock);
+ return ret;
+}
+EXPORT_SYMBOL(dget_parent);
+
+static struct dentry * __d_find_any_alias(struct inode *inode)
+{
+ struct dentry *alias;
+
+ if (hlist_empty(&inode->i_dentry))
+ return NULL;
+ alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
+ __dget(alias);
+ return alias;
+}
+
+/**
+ * d_find_any_alias - find any alias for a given inode
+ * @inode: inode to find an alias for
+ *
+ * If any aliases exist for the given inode, take and return a
+ * reference for one of them. If no aliases exist, return %NULL.
+ */
+struct dentry *d_find_any_alias(struct inode *inode)
+{
+ struct dentry *de;
+
+ spin_lock(&inode->i_lock);
+ de = __d_find_any_alias(inode);
+ spin_unlock(&inode->i_lock);
+ return de;
+}
+EXPORT_SYMBOL(d_find_any_alias);
+
+/**
+ * d_find_alias - grab a hashed alias of inode
+ * @inode: inode in question
+ *
+ * If inode has a hashed alias, or is a directory and has any alias,
+ * acquire the reference to alias and return it. Otherwise return NULL.
+ * Notice that if inode is a directory there can be only one alias and
+ * it can be unhashed only if it has no children, or if it is the root
+ * of a filesystem, or if the directory was renamed and d_revalidate
+ * was the first vfs operation to notice.
+ *
+ * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
+ * any other hashed alias over that one.
+ */
+static struct dentry *__d_find_alias(struct inode *inode)
+{
+ struct dentry *alias;
+
+ if (S_ISDIR(inode->i_mode))
+ return __d_find_any_alias(inode);
+
+ hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+ spin_lock(&alias->d_lock);
+ if (!d_unhashed(alias)) {
+ __dget_dlock(alias);
+ spin_unlock(&alias->d_lock);
+ return alias;
+ }
+ spin_unlock(&alias->d_lock);
+ }
+ return NULL;
+}
+
+struct dentry *d_find_alias(struct inode *inode)
+{
+ struct dentry *de = NULL;
+
+ if (!hlist_empty(&inode->i_dentry)) {
+ spin_lock(&inode->i_lock);
+ de = __d_find_alias(inode);
+ spin_unlock(&inode->i_lock);
+ }
+ return de;
+}
+EXPORT_SYMBOL(d_find_alias);
+
+/*
+ * Try to kill dentries associated with this inode.
+ * WARNING: you must own a reference to inode.
+ */
+void d_prune_aliases(struct inode *inode)
+{
+ struct dentry *dentry;
+restart:
+ spin_lock(&inode->i_lock);
+ hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
+ spin_lock(&dentry->d_lock);
+ if (!dentry->d_lockref.count) {
+ struct dentry *parent = lock_parent(dentry);
+ if (likely(!dentry->d_lockref.count)) {
+ __dentry_kill(dentry);
+ dput(parent);
+ goto restart;
+ }
+ if (parent)
+ spin_unlock(&parent->d_lock);
+ }
+ spin_unlock(&dentry->d_lock);
+ }
+ spin_unlock(&inode->i_lock);
+}
+EXPORT_SYMBOL(d_prune_aliases);
+
+/*
+ * Lock a dentry from shrink list.
+ * Called under rcu_read_lock() and dentry->d_lock; the former
+ * guarantees that nothing we access will be freed under us.
+ * Note that dentry is *not* protected from concurrent dentry_kill(),
+ * d_delete(), etc.
+ *
+ * Return false if dentry has been disrupted or grabbed, leaving
+ * the caller to kick it off-list. Otherwise, return true and have
+ * that dentry's inode and parent both locked.
+ */
+static bool shrink_lock_dentry(struct dentry *dentry)
+{
+ struct inode *inode;
+ struct dentry *parent;
+
+ if (dentry->d_lockref.count)
+ return false;
+
+ inode = dentry->d_inode;
+ if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
+ spin_unlock(&dentry->d_lock);
+ spin_lock(&inode->i_lock);
+ spin_lock(&dentry->d_lock);
+ if (unlikely(dentry->d_lockref.count))
+ goto out;
+ /* changed inode means that somebody had grabbed it */
+ if (unlikely(inode != dentry->d_inode))
+ goto out;
+ }
+
+ parent = dentry->d_parent;
+ if (IS_ROOT(dentry) || likely(spin_trylock(&parent->d_lock)))
+ return true;
+
+ spin_unlock(&dentry->d_lock);
+ spin_lock(&parent->d_lock);
+ if (unlikely(parent != dentry->d_parent)) {
+ spin_unlock(&parent->d_lock);
+ spin_lock(&dentry->d_lock);
+ goto out;
+ }
+ spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+ if (likely(!dentry->d_lockref.count))
+ return true;
+ spin_unlock(&parent->d_lock);
+out:
+ if (inode)
+ spin_unlock(&inode->i_lock);
+ return false;
+}
+
+static void shrink_dentry_list(struct list_head *list)
+{
+ while (!list_empty(list)) {
+ struct dentry *dentry, *parent;
+
+ dentry = list_entry(list->prev, struct dentry, d_lru);
+ spin_lock(&dentry->d_lock);
+ rcu_read_lock();
+ if (!shrink_lock_dentry(dentry)) {
+ bool can_free = false;
+ rcu_read_unlock();
+ d_shrink_del(dentry);
+ if (dentry->d_lockref.count < 0)
+ can_free = dentry->d_flags & DCACHE_MAY_FREE;
+ spin_unlock(&dentry->d_lock);
+ if (can_free)
+ dentry_free(dentry);
+ continue;
+ }
+ rcu_read_unlock();
+ d_shrink_del(dentry);
+ parent = dentry->d_parent;
+ __dentry_kill(dentry);
+ if (parent == dentry)
+ continue;
+ /*
+ * We need to prune ancestors too. This is necessary to prevent
+ * quadratic behavior of shrink_dcache_parent(), but is also
+ * expected to be beneficial in reducing dentry cache
+ * fragmentation.
+ */
+ dentry = parent;
+ while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
+ dentry = dentry_kill(dentry);
+ }
+}
+
+static enum lru_status dentry_lru_isolate(struct list_head *item,
+ struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
+{
+ struct list_head *freeable = arg;
+ struct dentry *dentry = container_of(item, struct dentry, d_lru);
+
+
+ /*
+ * we are inverting the lru lock/dentry->d_lock here,
+ * so use a trylock. If we fail to get the lock, just skip
+ * it
+ */
+ if (!spin_trylock(&dentry->d_lock))
+ return LRU_SKIP;
+
+ /*
+ * Referenced dentries are still in use. If they have active
+ * counts, just remove them from the LRU. Otherwise give them
+ * another pass through the LRU.
+ */
+ if (dentry->d_lockref.count) {
+ d_lru_isolate(lru, dentry);
+ spin_unlock(&dentry->d_lock);
+ return LRU_REMOVED;
+ }
+
+ if (dentry->d_flags & DCACHE_REFERENCED) {
+ dentry->d_flags &= ~DCACHE_REFERENCED;
+ spin_unlock(&dentry->d_lock);
+
+ /*
+ * The list move itself will be made by the common LRU code. At
+ * this point, we've dropped the dentry->d_lock but keep the
+ * lru lock. This is safe to do, since every list movement is
+ * protected by the lru lock even if both locks are held.
+ *
+ * This is guaranteed by the fact that all LRU management
+ * functions are intermediated by the LRU API calls like
+ * list_lru_add and list_lru_del. List movement in this file
+ * only ever occur through this functions or through callbacks
+ * like this one, that are called from the LRU API.
+ *
+ * The only exceptions to this are functions like
+ * shrink_dentry_list, and code that first checks for the
+ * DCACHE_SHRINK_LIST flag. Those are guaranteed to be
+ * operating only with stack provided lists after they are
+ * properly isolated from the main list. It is thus, always a
+ * local access.
+ */
+ return LRU_ROTATE;
+ }
+
+ d_lru_shrink_move(lru, dentry, freeable);
+ spin_unlock(&dentry->d_lock);
+
+ return LRU_REMOVED;
+}
+
+/**
+ * prune_dcache_sb - shrink the dcache
+ * @sb: superblock
+ * @sc: shrink control, passed to list_lru_shrink_walk()
+ *
+ * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
+ * is done when we need more memory and called from the superblock shrinker
+ * function.
+ *
+ * This function may fail to free any resources if all the dentries are in
+ * use.
+ */
+long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
+{
+ LIST_HEAD(dispose);
+ long freed;
+
+ freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
+ dentry_lru_isolate, &dispose);
+ shrink_dentry_list(&dispose);
+ return freed;
+}
+
+static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
+ struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
+{
+ struct list_head *freeable = arg;
+ struct dentry *dentry = container_of(item, struct dentry, d_lru);
+
+ /*
+ * we are inverting the lru lock/dentry->d_lock here,
+ * so use a trylock. If we fail to get the lock, just skip
+ * it
+ */
+ if (!spin_trylock(&dentry->d_lock))
+ return LRU_SKIP;
+
+ d_lru_shrink_move(lru, dentry, freeable);
+ spin_unlock(&dentry->d_lock);
+
+ return LRU_REMOVED;
+}
+
+
+/**
+ * shrink_dcache_sb - shrink dcache for a superblock
+ * @sb: superblock
+ *
+ * Shrink the dcache for the specified super block. This is used to free
+ * the dcache before unmounting a file system.
+ */
+void shrink_dcache_sb(struct super_block *sb)
+{
+ long freed;
+
+ do {
+ LIST_HEAD(dispose);
+
+ freed = list_lru_walk(&sb->s_dentry_lru,
+ dentry_lru_isolate_shrink, &dispose, 1024);
+
+ this_cpu_sub(nr_dentry_unused, freed);
+ shrink_dentry_list(&dispose);
+ } while (list_lru_count(&sb->s_dentry_lru) > 0);
+}
+EXPORT_SYMBOL(shrink_dcache_sb);
+
+/**
+ * enum d_walk_ret - action to talke during tree walk
+ * @D_WALK_CONTINUE: contrinue walk
+ * @D_WALK_QUIT: quit walk
+ * @D_WALK_NORETRY: quit when retry is needed
+ * @D_WALK_SKIP: skip this dentry and its children
+ */
+enum d_walk_ret {
+ D_WALK_CONTINUE,
+ D_WALK_QUIT,
+ D_WALK_NORETRY,
+ D_WALK_SKIP,
+};
+
+/**
+ * d_walk - walk the dentry tree
+ * @parent: start of walk
+ * @data: data passed to @enter() and @finish()
+ * @enter: callback when first entering the dentry
+ *
+ * The @enter() callbacks are called with d_lock held.
+ */
+static void d_walk(struct dentry *parent, void *data,
+ enum d_walk_ret (*enter)(void *, struct dentry *))
+{
+ struct dentry *this_parent;
+ struct list_head *next;
+ unsigned seq = 0;
+ enum d_walk_ret ret;
+ bool retry = true;
+
+again:
+ read_seqbegin_or_lock(&rename_lock, &seq);
+ this_parent = parent;
+ spin_lock(&this_parent->d_lock);
+
+ ret = enter(data, this_parent);
+ switch (ret) {
+ case D_WALK_CONTINUE:
+ break;
+ case D_WALK_QUIT:
+ case D_WALK_SKIP:
+ goto out_unlock;
+ case D_WALK_NORETRY:
+ retry = false;
+ break;
+ }
+repeat:
+ next = this_parent->d_subdirs.next;
+resume:
+ while (next != &this_parent->d_subdirs) {
+ struct list_head *tmp = next;
+ struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
+ next = tmp->next;
+
+ if (unlikely(dentry->d_flags & DCACHE_DENTRY_CURSOR))
+ continue;
+
+ spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+
+ ret = enter(data, dentry);
+ switch (ret) {
+ case D_WALK_CONTINUE:
+ break;
+ case D_WALK_QUIT:
+ spin_unlock(&dentry->d_lock);
+ goto out_unlock;
+ case D_WALK_NORETRY:
+ retry = false;
+ break;
+ case D_WALK_SKIP:
+ spin_unlock(&dentry->d_lock);
+ continue;
+ }
+
+ if (!list_empty(&dentry->d_subdirs)) {
+ spin_unlock(&this_parent->d_lock);
+ spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
+ this_parent = dentry;
+ spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
+ goto repeat;
+ }
+ spin_unlock(&dentry->d_lock);
+ }
+ /*
+ * All done at this level ... ascend and resume the search.
+ */
+ rcu_read_lock();
+ascend:
+ if (this_parent != parent) {
+ struct dentry *child = this_parent;
+ this_parent = child->d_parent;
+
+ spin_unlock(&child->d_lock);
+ spin_lock(&this_parent->d_lock);
+
+ /* might go back up the wrong parent if we have had a rename. */
+ if (need_seqretry(&rename_lock, seq))
+ goto rename_retry;
+ /* go into the first sibling still alive */
+ do {
+ next = child->d_child.next;
+ if (next == &this_parent->d_subdirs)
+ goto ascend;
+ child = list_entry(next, struct dentry, d_child);
+ } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
+ rcu_read_unlock();
+ goto resume;
+ }
+ if (need_seqretry(&rename_lock, seq))
+ goto rename_retry;
+ rcu_read_unlock();
+
+out_unlock:
+ spin_unlock(&this_parent->d_lock);
+ done_seqretry(&rename_lock, seq);
+ return;
+
+rename_retry:
+ spin_unlock(&this_parent->d_lock);
+ rcu_read_unlock();
+ BUG_ON(seq & 1);
+ if (!retry)
+ return;
+ seq = 1;
+ goto again;
+}
+
+struct check_mount {
+ struct vfsmount *mnt;
+ unsigned int mounted;
+};
+
+static enum d_walk_ret path_check_mount(void *data, struct dentry *dentry)
+{
+ struct check_mount *info = data;
+ struct path path = { .mnt = info->mnt, .dentry = dentry };
+
+ if (likely(!d_mountpoint(dentry)))
+ return D_WALK_CONTINUE;
+ if (__path_is_mountpoint(&path)) {
+ info->mounted = 1;
+ return D_WALK_QUIT;
+ }
+ return D_WALK_CONTINUE;
+}
+
+/**
+ * path_has_submounts - check for mounts over a dentry in the
+ * current namespace.
+ * @parent: path to check.
+ *
+ * Return true if the parent or its subdirectories contain
+ * a mount point in the current namespace.
+ */
+int path_has_submounts(const struct path *parent)
+{
+ struct check_mount data = { .mnt = parent->mnt, .mounted = 0 };
+
+ read_seqlock_excl(&mount_lock);
+ d_walk(parent->dentry, &data, path_check_mount);
+ read_sequnlock_excl(&mount_lock);
+
+ return data.mounted;
+}
+EXPORT_SYMBOL(path_has_submounts);
+
+/*
+ * Called by mount code to set a mountpoint and check if the mountpoint is
+ * reachable (e.g. NFS can unhash a directory dentry and then the complete
+ * subtree can become unreachable).
+ *
+ * Only one of d_invalidate() and d_set_mounted() must succeed. For
+ * this reason take rename_lock and d_lock on dentry and ancestors.
+ */
+int d_set_mounted(struct dentry *dentry)
+{
+ struct dentry *p;
+ int ret = -ENOENT;
+ write_seqlock(&rename_lock);
+ for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
+ /* Need exclusion wrt. d_invalidate() */
+ spin_lock(&p->d_lock);
+ if (unlikely(d_unhashed(p))) {
+ spin_unlock(&p->d_lock);
+ goto out;
+ }
+ spin_unlock(&p->d_lock);
+ }
+ spin_lock(&dentry->d_lock);
+ if (!d_unlinked(dentry)) {
+ ret = -EBUSY;
+ if (!d_mountpoint(dentry)) {
+ dentry->d_flags |= DCACHE_MOUNTED;
+ ret = 0;
+ }
+ }
+ spin_unlock(&dentry->d_lock);
+out:
+ write_sequnlock(&rename_lock);
+ return ret;
+}
+
+/*
+ * Search the dentry child list of the specified parent,
+ * and move any unused dentries to the end of the unused
+ * list for prune_dcache(). We descend to the next level
+ * whenever the d_subdirs list is non-empty and continue
+ * searching.
+ *
+ * It returns zero iff there are no unused children,
+ * otherwise it returns the number of children moved to
+ * the end of the unused list. This may not be the total
+ * number of unused children, because select_parent can
+ * drop the lock and return early due to latency
+ * constraints.
+ */
+
+struct select_data {
+ struct dentry *start;
+ struct list_head dispose;
+ int found;
+};
+
+static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
+{
+ struct select_data *data = _data;
+ enum d_walk_ret ret = D_WALK_CONTINUE;
+
+ if (data->start == dentry)
+ goto out;
+
+ if (dentry->d_flags & DCACHE_SHRINK_LIST) {
+ data->found++;
+ } else {
+ if (dentry->d_flags & DCACHE_LRU_LIST)
+ d_lru_del(dentry);
+ if (!dentry->d_lockref.count) {
+ d_shrink_add(dentry, &data->dispose);
+ data->found++;
+ }
+ }
+ /*
+ * We can return to the caller if we have found some (this
+ * ensures forward progress). We'll be coming back to find
+ * the rest.
+ */
+ if (!list_empty(&data->dispose))
+ ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
+out:
+ return ret;
+}
+
+/**
+ * shrink_dcache_parent - prune dcache
+ * @parent: parent of entries to prune
+ *
+ * Prune the dcache to remove unused children of the parent dentry.
+ */
+void shrink_dcache_parent(struct dentry *parent)
+{
+ for (;;) {
+ struct select_data data;
+
+ INIT_LIST_HEAD(&data.dispose);
+ data.start = parent;
+ data.found = 0;
+
+ d_walk(parent, &data, select_collect);
+
+ if (!list_empty(&data.dispose)) {
+ shrink_dentry_list(&data.dispose);
+ continue;
+ }
+
+ cond_resched();
+ if (!data.found)
+ break;
+ }
+}
+EXPORT_SYMBOL(shrink_dcache_parent);
+
+static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
+{
+ /* it has busy descendents; complain about those instead */
+ if (!list_empty(&dentry->d_subdirs))
+ return D_WALK_CONTINUE;
+
+ /* root with refcount 1 is fine */
+ if (dentry == _data && dentry->d_lockref.count == 1)
+ return D_WALK_CONTINUE;
+
+ printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
+ " still in use (%d) [unmount of %s %s]\n",
+ dentry,
+ dentry->d_inode ?
+ dentry->d_inode->i_ino : 0UL,
+ dentry,
+ dentry->d_lockref.count,
+ dentry->d_sb->s_type->name,
+ dentry->d_sb->s_id);
+ WARN_ON(1);
+ return D_WALK_CONTINUE;
+}
+
+static void do_one_tree(struct dentry *dentry)
+{
+ shrink_dcache_parent(dentry);
+ d_walk(dentry, dentry, umount_check);
+ d_drop(dentry);
+ dput(dentry);
+}
+
+/*
+ * destroy the dentries attached to a superblock on unmounting
+ */
+void shrink_dcache_for_umount(struct super_block *sb)
+{
+ struct dentry *dentry;
+
+ WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
+
+ dentry = sb->s_root;
+ sb->s_root = NULL;
+ do_one_tree(dentry);
+
+ while (!hlist_bl_empty(&sb->s_roots)) {
+ dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_roots), struct dentry, d_hash));
+ do_one_tree(dentry);
+ }
+}
+
+static enum d_walk_ret find_submount(void *_data, struct dentry *dentry)
+{
+ struct dentry **victim = _data;
+ if (d_mountpoint(dentry)) {
+ __dget_dlock(dentry);
+ *victim = dentry;
+ return D_WALK_QUIT;
+ }
+ return D_WALK_CONTINUE;
+}
+
+/**
+ * d_invalidate - detach submounts, prune dcache, and drop
+ * @dentry: dentry to invalidate (aka detach, prune and drop)
+ */
+void d_invalidate(struct dentry *dentry)
+{
+ bool had_submounts = false;
+ spin_lock(&dentry->d_lock);
+ if (d_unhashed(dentry)) {
+ spin_unlock(&dentry->d_lock);
+ return;
+ }
+ __d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
+
+ /* Negative dentries can be dropped without further checks */
+ if (!dentry->d_inode)
+ return;
+
+ shrink_dcache_parent(dentry);
+ for (;;) {
+ struct dentry *victim = NULL;
+ d_walk(dentry, &victim, find_submount);
+ if (!victim) {
+ if (had_submounts)
+ shrink_dcache_parent(dentry);
+ return;
+ }
+ had_submounts = true;
+ detach_mounts(victim);
+ dput(victim);
+ }
+}
+EXPORT_SYMBOL(d_invalidate);
+
+/**
+ * __d_alloc - allocate a dcache entry
+ * @sb: filesystem it will belong to
+ * @name: qstr of the name
+ *
+ * Allocates a dentry. It returns %NULL if there is insufficient memory
+ * available. On a success the dentry is returned. The name passed in is
+ * copied and the copy passed in may be reused after this call.
+ */
+
+struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
+{
+ struct external_name *ext = NULL;
+ struct dentry *dentry;
+ char *dname;
+ int err;
+
+ dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
+ if (!dentry)
+ return NULL;
+
+ /*
+ * We guarantee that the inline name is always NUL-terminated.
+ * This way the memcpy() done by the name switching in rename
+ * will still always have a NUL at the end, even if we might
+ * be overwriting an internal NUL character
+ */
+ dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
+ if (unlikely(!name)) {
+ name = &slash_name;
+ dname = dentry->d_iname;
+ } else if (name->len > DNAME_INLINE_LEN-1) {
+ size_t size = offsetof(struct external_name, name[1]);
+
+ ext = kmalloc(size + name->len, GFP_KERNEL_ACCOUNT);
+ if (!ext) {
+ kmem_cache_free(dentry_cache, dentry);
+ return NULL;
+ }
+ atomic_set(&ext->u.count, 1);
+ dname = ext->name;
+ } else {
+ dname = dentry->d_iname;
+ }
+
+ dentry->d_name.len = name->len;
+ dentry->d_name.hash = name->hash;
+ memcpy(dname, name->name, name->len);
+ dname[name->len] = 0;
+
+ /* Make sure we always see the terminating NUL character */
+ smp_store_release(&dentry->d_name.name, dname); /* ^^^ */
+
+ dentry->d_lockref.count = 1;
+ dentry->d_flags = 0;
+ spin_lock_init(&dentry->d_lock);
+ seqcount_init(&dentry->d_seq);
+ dentry->d_inode = NULL;
+ dentry->d_parent = dentry;
+ dentry->d_sb = sb;
+ dentry->d_op = NULL;
+ dentry->d_fsdata = NULL;
+ INIT_HLIST_BL_NODE(&dentry->d_hash);
+ INIT_LIST_HEAD(&dentry->d_lru);
+ INIT_LIST_HEAD(&dentry->d_subdirs);
+ INIT_HLIST_NODE(&dentry->d_u.d_alias);
+ INIT_LIST_HEAD(&dentry->d_child);
+ d_set_d_op(dentry, dentry->d_sb->s_d_op);
+
+ if (dentry->d_op && dentry->d_op->d_init) {
+ err = dentry->d_op->d_init(dentry);
+ if (err) {
+ if (dname_external(dentry))
+ kfree(external_name(dentry));
+ kmem_cache_free(dentry_cache, dentry);
+ return NULL;
+ }
+ }
+
+ if (unlikely(ext)) {
+ pg_data_t *pgdat = page_pgdat(virt_to_page(ext));
+ mod_node_page_state(pgdat, NR_INDIRECTLY_RECLAIMABLE_BYTES,
+ ksize(ext));
+ }
+
+ this_cpu_inc(nr_dentry);
+
+ return dentry;
+}
+
+/**
+ * d_alloc - allocate a dcache entry
+ * @parent: parent of entry to allocate
+ * @name: qstr of the name
+ *
+ * Allocates a dentry. It returns %NULL if there is insufficient memory
+ * available. On a success the dentry is returned. The name passed in is
+ * copied and the copy passed in may be reused after this call.
+ */
+struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
+{
+ struct dentry *dentry = __d_alloc(parent->d_sb, name);
+ if (!dentry)
+ return NULL;
+ dentry->d_flags |= DCACHE_RCUACCESS;
+ spin_lock(&parent->d_lock);
+ /*
+ * don't need child lock because it is not subject
+ * to concurrency here
+ */
+ __dget_dlock(parent);
+ dentry->d_parent = parent;
+ list_add(&dentry->d_child, &parent->d_subdirs);
+ spin_unlock(&parent->d_lock);
+
+ return dentry;
+}
+EXPORT_SYMBOL(d_alloc);
+
+struct dentry *d_alloc_anon(struct super_block *sb)
+{
+ return __d_alloc(sb, NULL);
+}
+EXPORT_SYMBOL(d_alloc_anon);
+
+struct dentry *d_alloc_cursor(struct dentry * parent)
+{
+ struct dentry *dentry = d_alloc_anon(parent->d_sb);
+ if (dentry) {
+ dentry->d_flags |= DCACHE_RCUACCESS | DCACHE_DENTRY_CURSOR;
+ dentry->d_parent = dget(parent);
+ }
+ return dentry;
+}
+
+/**
+ * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
+ * @sb: the superblock
+ * @name: qstr of the name
+ *
+ * For a filesystem that just pins its dentries in memory and never
+ * performs lookups at all, return an unhashed IS_ROOT dentry.
+ */
+struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
+{
+ return __d_alloc(sb, name);
+}
+EXPORT_SYMBOL(d_alloc_pseudo);
+
+struct dentry *d_alloc_name(struct dentry *parent, const char *name)
+{
+ struct qstr q;
+
+ q.name = name;
+ q.hash_len = hashlen_string(parent, name);
+ return d_alloc(parent, &q);
+}
+EXPORT_SYMBOL(d_alloc_name);
+
+void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
+{
+ WARN_ON_ONCE(dentry->d_op);
+ WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH |
+ DCACHE_OP_COMPARE |
+ DCACHE_OP_REVALIDATE |
+ DCACHE_OP_WEAK_REVALIDATE |
+ DCACHE_OP_DELETE |
+ DCACHE_OP_REAL));
+ dentry->d_op = op;
+ if (!op)
+ return;
+ if (op->d_hash)
+ dentry->d_flags |= DCACHE_OP_HASH;
+ if (op->d_compare)
+ dentry->d_flags |= DCACHE_OP_COMPARE;
+ if (op->d_revalidate)
+ dentry->d_flags |= DCACHE_OP_REVALIDATE;
+ if (op->d_weak_revalidate)
+ dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
+ if (op->d_delete)
+ dentry->d_flags |= DCACHE_OP_DELETE;
+ if (op->d_prune)
+ dentry->d_flags |= DCACHE_OP_PRUNE;
+ if (op->d_real)
+ dentry->d_flags |= DCACHE_OP_REAL;
+
+}
+EXPORT_SYMBOL(d_set_d_op);
+
+
+/*
+ * d_set_fallthru - Mark a dentry as falling through to a lower layer
+ * @dentry - The dentry to mark
+ *
+ * Mark a dentry as falling through to the lower layer (as set with
+ * d_pin_lower()). This flag may be recorded on the medium.
+ */
+void d_set_fallthru(struct dentry *dentry)
+{
+ spin_lock(&dentry->d_lock);
+ dentry->d_flags |= DCACHE_FALLTHRU;
+ spin_unlock(&dentry->d_lock);
+}
+EXPORT_SYMBOL(d_set_fallthru);
+
+static unsigned d_flags_for_inode(struct inode *inode)
+{
+ unsigned add_flags = DCACHE_REGULAR_TYPE;
+
+ if (!inode)
+ return DCACHE_MISS_TYPE;
+
+ if (S_ISDIR(inode->i_mode)) {
+ add_flags = DCACHE_DIRECTORY_TYPE;
+ if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
+ if (unlikely(!inode->i_op->lookup))
+ add_flags = DCACHE_AUTODIR_TYPE;
+ else
+ inode->i_opflags |= IOP_LOOKUP;
+ }
+ goto type_determined;
+ }
+
+ if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
+ if (unlikely(inode->i_op->get_link)) {
+ add_flags = DCACHE_SYMLINK_TYPE;
+ goto type_determined;
+ }
+ inode->i_opflags |= IOP_NOFOLLOW;
+ }
+
+ if (unlikely(!S_ISREG(inode->i_mode)))
+ add_flags = DCACHE_SPECIAL_TYPE;
+
+type_determined:
+ if (unlikely(IS_AUTOMOUNT(inode)))
+ add_flags |= DCACHE_NEED_AUTOMOUNT;
+ return add_flags;
+}
+
+static void __d_instantiate(struct dentry *dentry, struct inode *inode)
+{
+ unsigned add_flags = d_flags_for_inode(inode);
+ WARN_ON(d_in_lookup(dentry));
+
+ spin_lock(&dentry->d_lock);
+ hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
+ raw_write_seqcount_begin(&dentry->d_seq);
+ __d_set_inode_and_type(dentry, inode, add_flags);
+ raw_write_seqcount_end(&dentry->d_seq);
+ fsnotify_update_flags(dentry);
+ spin_unlock(&dentry->d_lock);
+}
+
+/**
+ * d_instantiate - fill in inode information for a dentry
+ * @entry: dentry to complete
+ * @inode: inode to attach to this dentry
+ *
+ * Fill in inode information in the entry.
+ *
+ * This turns negative dentries into productive full members
+ * of society.
+ *
+ * NOTE! This assumes that the inode count has been incremented
+ * (or otherwise set) by the caller to indicate that it is now
+ * in use by the dcache.
+ */
+
+void d_instantiate(struct dentry *entry, struct inode * inode)
+{
+ BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
+ if (inode) {
+ security_d_instantiate(entry, inode);
+ spin_lock(&inode->i_lock);
+ __d_instantiate(entry, inode);
+ spin_unlock(&inode->i_lock);
+ }
+}
+EXPORT_SYMBOL(d_instantiate);
+
+/*
+ * This should be equivalent to d_instantiate() + unlock_new_inode(),
+ * with lockdep-related part of unlock_new_inode() done before
+ * anything else. Use that instead of open-coding d_instantiate()/
+ * unlock_new_inode() combinations.
+ */
+void d_instantiate_new(struct dentry *entry, struct inode *inode)
+{
+ BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
+ BUG_ON(!inode);
+ lockdep_annotate_inode_mutex_key(inode);
+ security_d_instantiate(entry, inode);
+ spin_lock(&inode->i_lock);
+ __d_instantiate(entry, inode);
+ WARN_ON(!(inode->i_state & I_NEW));
+ inode->i_state &= ~I_NEW & ~I_CREATING;
+ smp_mb();
+ wake_up_bit(&inode->i_state, __I_NEW);
+ spin_unlock(&inode->i_lock);
+}
+EXPORT_SYMBOL(d_instantiate_new);
+
+struct dentry *d_make_root(struct inode *root_inode)
+{
+ struct dentry *res = NULL;
+
+ if (root_inode) {
+ res = d_alloc_anon(root_inode->i_sb);
+ if (res) {
+ res->d_flags |= DCACHE_RCUACCESS;
+ d_instantiate(res, root_inode);
+ } else {
+ iput(root_inode);
+ }
+ }
+ return res;
+}
+EXPORT_SYMBOL(d_make_root);
+
+static struct dentry *__d_instantiate_anon(struct dentry *dentry,
+ struct inode *inode,
+ bool disconnected)
+{
+ struct dentry *res;
+ unsigned add_flags;
+
+ security_d_instantiate(dentry, inode);
+ spin_lock(&inode->i_lock);
+ res = __d_find_any_alias(inode);
+ if (res) {
+ spin_unlock(&inode->i_lock);
+ dput(dentry);
+ goto out_iput;
+ }
+
+ /* attach a disconnected dentry */
+ add_flags = d_flags_for_inode(inode);
+
+ if (disconnected)
+ add_flags |= DCACHE_DISCONNECTED;
+
+ spin_lock(&dentry->d_lock);
+ __d_set_inode_and_type(dentry, inode, add_flags);
+ hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
+ if (!disconnected) {
+ hlist_bl_lock(&dentry->d_sb->s_roots);
+ hlist_bl_add_head(&dentry->d_hash, &dentry->d_sb->s_roots);
+ hlist_bl_unlock(&dentry->d_sb->s_roots);
+ }
+ spin_unlock(&dentry->d_lock);
+ spin_unlock(&inode->i_lock);
+
+ return dentry;
+
+ out_iput:
+ iput(inode);
+ return res;
+}
+
+struct dentry *d_instantiate_anon(struct dentry *dentry, struct inode *inode)
+{
+ return __d_instantiate_anon(dentry, inode, true);
+}
+EXPORT_SYMBOL(d_instantiate_anon);
+
+static struct dentry *__d_obtain_alias(struct inode *inode, bool disconnected)
+{
+ struct dentry *tmp;
+ struct dentry *res;
+
+ if (!inode)
+ return ERR_PTR(-ESTALE);
+ if (IS_ERR(inode))
+ return ERR_CAST(inode);
+
+ res = d_find_any_alias(inode);
+ if (res)
+ goto out_iput;
+
+ tmp = d_alloc_anon(inode->i_sb);
+ if (!tmp) {
+ res = ERR_PTR(-ENOMEM);
+ goto out_iput;
+ }
+
+ return __d_instantiate_anon(tmp, inode, disconnected);
+
+out_iput:
+ iput(inode);
+ return res;
+}
+
+/**
+ * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
+ * @inode: inode to allocate the dentry for
+ *
+ * Obtain a dentry for an inode resulting from NFS filehandle conversion or
+ * similar open by handle operations. The returned dentry may be anonymous,
+ * or may have a full name (if the inode was already in the cache).
+ *
+ * When called on a directory inode, we must ensure that the inode only ever
+ * has one dentry. If a dentry is found, that is returned instead of
+ * allocating a new one.
+ *
+ * On successful return, the reference to the inode has been transferred
+ * to the dentry. In case of an error the reference on the inode is released.
+ * To make it easier to use in export operations a %NULL or IS_ERR inode may
+ * be passed in and the error will be propagated to the return value,
+ * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
+ */
+struct dentry *d_obtain_alias(struct inode *inode)
+{
+ return __d_obtain_alias(inode, true);
+}
+EXPORT_SYMBOL(d_obtain_alias);
+
+/**
+ * d_obtain_root - find or allocate a dentry for a given inode
+ * @inode: inode to allocate the dentry for
+ *
+ * Obtain an IS_ROOT dentry for the root of a filesystem.
+ *
+ * We must ensure that directory inodes only ever have one dentry. If a
+ * dentry is found, that is returned instead of allocating a new one.
+ *
+ * On successful return, the reference to the inode has been transferred
+ * to the dentry. In case of an error the reference on the inode is
+ * released. A %NULL or IS_ERR inode may be passed in and will be the
+ * error will be propagate to the return value, with a %NULL @inode
+ * replaced by ERR_PTR(-ESTALE).
+ */
+struct dentry *d_obtain_root(struct inode *inode)
+{
+ return __d_obtain_alias(inode, false);
+}
+EXPORT_SYMBOL(d_obtain_root);
+
+/**
+ * d_add_ci - lookup or allocate new dentry with case-exact name
+ * @inode: the inode case-insensitive lookup has found
+ * @dentry: the negative dentry that was passed to the parent's lookup func
+ * @name: the case-exact name to be associated with the returned dentry
+ *
+ * This is to avoid filling the dcache with case-insensitive names to the
+ * same inode, only the actual correct case is stored in the dcache for
+ * case-insensitive filesystems.
+ *
+ * For a case-insensitive lookup match and if the the case-exact dentry
+ * already exists in in the dcache, use it and return it.
+ *
+ * If no entry exists with the exact case name, allocate new dentry with
+ * the exact case, and return the spliced entry.
+ */
+struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
+ struct qstr *name)
+{
+ struct dentry *found, *res;
+
+ /*
+ * First check if a dentry matching the name already exists,
+ * if not go ahead and create it now.
+ */
+ found = d_hash_and_lookup(dentry->d_parent, name);
+ if (found) {
+ iput(inode);
+ return found;
+ }
+ if (d_in_lookup(dentry)) {
+ found = d_alloc_parallel(dentry->d_parent, name,
+ dentry->d_wait);
+ if (IS_ERR(found) || !d_in_lookup(found)) {
+ iput(inode);
+ return found;
+ }
+ } else {
+ found = d_alloc(dentry->d_parent, name);
+ if (!found) {
+ iput(inode);
+ return ERR_PTR(-ENOMEM);
+ }
+ }
+ res = d_splice_alias(inode, found);
+ if (res) {
+ dput(found);
+ return res;
+ }
+ return found;
+}
+EXPORT_SYMBOL(d_add_ci);
+
+
+static inline bool d_same_name(const struct dentry *dentry,
+ const struct dentry *parent,
+ const struct qstr *name)
+{
+ if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
+ if (dentry->d_name.len != name->len)
+ return false;
+ return dentry_cmp(dentry, name->name, name->len) == 0;
+ }
+ return parent->d_op->d_compare(dentry,
+ dentry->d_name.len, dentry->d_name.name,
+ name) == 0;
+}
+
+/**
+ * __d_lookup_rcu - search for a dentry (racy, store-free)
+ * @parent: parent dentry
+ * @name: qstr of name we wish to find
+ * @seqp: returns d_seq value at the point where the dentry was found
+ * Returns: dentry, or NULL
+ *
+ * __d_lookup_rcu is the dcache lookup function for rcu-walk name
+ * resolution (store-free path walking) design described in
+ * Documentation/filesystems/path-lookup.txt.
+ *
+ * This is not to be used outside core vfs.
+ *
+ * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
+ * held, and rcu_read_lock held. The returned dentry must not be stored into
+ * without taking d_lock and checking d_seq sequence count against @seq
+ * returned here.
+ *
+ * A refcount may be taken on the found dentry with the d_rcu_to_refcount
+ * function.
+ *
+ * Alternatively, __d_lookup_rcu may be called again to look up the child of
+ * the returned dentry, so long as its parent's seqlock is checked after the
+ * child is looked up. Thus, an interlocking stepping of sequence lock checks
+ * is formed, giving integrity down the path walk.
+ *
+ * NOTE! The caller *has* to check the resulting dentry against the sequence
+ * number we've returned before using any of the resulting dentry state!
+ */
+struct dentry *__d_lookup_rcu(const struct dentry *parent,
+ const struct qstr *name,
+ unsigned *seqp)
+{
+ u64 hashlen = name->hash_len;
+ const unsigned char *str = name->name;
+ struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
+ struct hlist_bl_node *node;
+ struct dentry *dentry;
+
+ /*
+ * Note: There is significant duplication with __d_lookup_rcu which is
+ * required to prevent single threaded performance regressions
+ * especially on architectures where smp_rmb (in seqcounts) are costly.
+ * Keep the two functions in sync.
+ */
+
+ /*
+ * The hash list is protected using RCU.
+ *
+ * Carefully use d_seq when comparing a candidate dentry, to avoid
+ * races with d_move().
+ *
+ * It is possible that concurrent renames can mess up our list
+ * walk here and result in missing our dentry, resulting in the
+ * false-negative result. d_lookup() protects against concurrent
+ * renames using rename_lock seqlock.
+ *
+ * See Documentation/filesystems/path-lookup.txt for more details.
+ */
+ hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
+ unsigned seq;
+
+seqretry:
+ /*
+ * The dentry sequence count protects us from concurrent
+ * renames, and thus protects parent and name fields.
+ *
+ * The caller must perform a seqcount check in order
+ * to do anything useful with the returned dentry.
+ *
+ * NOTE! We do a "raw" seqcount_begin here. That means that
+ * we don't wait for the sequence count to stabilize if it
+ * is in the middle of a sequence change. If we do the slow
+ * dentry compare, we will do seqretries until it is stable,
+ * and if we end up with a successful lookup, we actually
+ * want to exit RCU lookup anyway.
+ *
+ * Note that raw_seqcount_begin still *does* smp_rmb(), so
+ * we are still guaranteed NUL-termination of ->d_name.name.
+ */
+ seq = raw_seqcount_begin(&dentry->d_seq);
+ if (dentry->d_parent != parent)
+ continue;
+ if (d_unhashed(dentry))
+ continue;
+
+ if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
+ int tlen;
+ const char *tname;
+ if (dentry->d_name.hash != hashlen_hash(hashlen))
+ continue;
+ tlen = dentry->d_name.len;
+ tname = dentry->d_name.name;
+ /* we want a consistent (name,len) pair */
+ if (read_seqcount_retry(&dentry->d_seq, seq)) {
+ cpu_relax();
+ goto seqretry;
+ }
+ if (parent->d_op->d_compare(dentry,
+ tlen, tname, name) != 0)
+ continue;
+ } else {
+ if (dentry->d_name.hash_len != hashlen)
+ continue;
+ if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
+ continue;
+ }
+ *seqp = seq;
+ return dentry;
+ }
+ return NULL;
+}
+
+/**
+ * d_lookup - search for a dentry
+ * @parent: parent dentry
+ * @name: qstr of name we wish to find
+ * Returns: dentry, or NULL
+ *
+ * d_lookup searches the children of the parent dentry for the name in
+ * question. If the dentry is found its reference count is incremented and the
+ * dentry is returned. The caller must use dput to free the entry when it has
+ * finished using it. %NULL is returned if the dentry does not exist.
+ */
+struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
+{
+ struct dentry *dentry;
+ unsigned seq;
+
+ do {
+ seq = read_seqbegin(&rename_lock);
+ dentry = __d_lookup(parent, name);
+ if (dentry)
+ break;
+ } while (read_seqretry(&rename_lock, seq));
+ return dentry;
+}
+EXPORT_SYMBOL(d_lookup);
+
+/**
+ * __d_lookup - search for a dentry (racy)
+ * @parent: parent dentry
+ * @name: qstr of name we wish to find
+ * Returns: dentry, or NULL
+ *
+ * __d_lookup is like d_lookup, however it may (rarely) return a
+ * false-negative result due to unrelated rename activity.
+ *
+ * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
+ * however it must be used carefully, eg. with a following d_lookup in
+ * the case of failure.
+ *
+ * __d_lookup callers must be commented.
+ */
+struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
+{
+ unsigned int hash = name->hash;
+ struct hlist_bl_head *b = d_hash(hash);
+ struct hlist_bl_node *node;
+ struct dentry *found = NULL;
+ struct dentry *dentry;
+
+ /*
+ * Note: There is significant duplication with __d_lookup_rcu which is
+ * required to prevent single threaded performance regressions
+ * especially on architectures where smp_rmb (in seqcounts) are costly.
+ * Keep the two functions in sync.
+ */
+
+ /*
+ * The hash list is protected using RCU.
+ *
+ * Take d_lock when comparing a candidate dentry, to avoid races
+ * with d_move().
+ *
+ * It is possible that concurrent renames can mess up our list
+ * walk here and result in missing our dentry, resulting in the
+ * false-negative result. d_lookup() protects against concurrent
+ * renames using rename_lock seqlock.
+ *
+ * See Documentation/filesystems/path-lookup.txt for more details.
+ */
+ rcu_read_lock();
+
+ hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
+
+ if (dentry->d_name.hash != hash)
+ continue;
+
+ spin_lock(&dentry->d_lock);
+ if (dentry->d_parent != parent)
+ goto next;
+ if (d_unhashed(dentry))
+ goto next;
+
+ if (!d_same_name(dentry, parent, name))
+ goto next;
+
+ dentry->d_lockref.count++;
+ found = dentry;
+ spin_unlock(&dentry->d_lock);
+ break;
+next:
+ spin_unlock(&dentry->d_lock);
+ }
+ rcu_read_unlock();
+
+ return found;
+}
+
+/**
+ * d_hash_and_lookup - hash the qstr then search for a dentry
+ * @dir: Directory to search in
+ * @name: qstr of name we wish to find
+ *
+ * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
+ */
+struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
+{
+ /*
+ * Check for a fs-specific hash function. Note that we must
+ * calculate the standard hash first, as the d_op->d_hash()
+ * routine may choose to leave the hash value unchanged.
+ */
+ name->hash = full_name_hash(dir, name->name, name->len);
+ if (dir->d_flags & DCACHE_OP_HASH) {
+ int err = dir->d_op->d_hash(dir, name);
+ if (unlikely(err < 0))
+ return ERR_PTR(err);
+ }
+ return d_lookup(dir, name);
+}
+EXPORT_SYMBOL(d_hash_and_lookup);
+
+/*
+ * When a file is deleted, we have two options:
+ * - turn this dentry into a negative dentry
+ * - unhash this dentry and free it.
+ *
+ * Usually, we want to just turn this into
+ * a negative dentry, but if anybody else is
+ * currently using the dentry or the inode
+ * we can't do that and we fall back on removing
+ * it from the hash queues and waiting for
+ * it to be deleted later when it has no users
+ */
+
+/**
+ * d_delete - delete a dentry
+ * @dentry: The dentry to delete
+ *
+ * Turn the dentry into a negative dentry if possible, otherwise
+ * remove it from the hash queues so it can be deleted later
+ */
+
+void d_delete(struct dentry * dentry)
+{
+ struct inode *inode = dentry->d_inode;
+ int isdir = d_is_dir(dentry);
+
+ spin_lock(&inode->i_lock);
+ spin_lock(&dentry->d_lock);
+ /*
+ * Are we the only user?
+ */
+ if (dentry->d_lockref.count == 1) {
+ dentry->d_flags &= ~DCACHE_CANT_MOUNT;
+ dentry_unlink_inode(dentry);
+ } else {
+ __d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
+ spin_unlock(&inode->i_lock);
+ }
+ fsnotify_nameremove(dentry, isdir);
+}
+EXPORT_SYMBOL(d_delete);
+
+static void __d_rehash(struct dentry *entry)
+{
+ struct hlist_bl_head *b = d_hash(entry->d_name.hash);
+
+ hlist_bl_lock(b);
+ hlist_bl_add_head_rcu(&entry->d_hash, b);
+ hlist_bl_unlock(b);
+}
+
+/**
+ * d_rehash - add an entry back to the hash
+ * @entry: dentry to add to the hash
+ *
+ * Adds a dentry to the hash according to its name.
+ */
+
+void d_rehash(struct dentry * entry)
+{
+ spin_lock(&entry->d_lock);
+ __d_rehash(entry);
+ spin_unlock(&entry->d_lock);
+}
+EXPORT_SYMBOL(d_rehash);
+
+static inline unsigned start_dir_add(struct inode *dir)
+{
+
+ for (;;) {
+ unsigned n = dir->i_dir_seq;
+ if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
+ return n;
+ cpu_relax();
+ }
+}
+
+static inline void end_dir_add(struct inode *dir, unsigned n)
+{
+ smp_store_release(&dir->i_dir_seq, n + 2);
+}
+
+static void d_wait_lookup(struct dentry *dentry)
+{
+ if (d_in_lookup(dentry)) {
+ DECLARE_WAITQUEUE(wait, current);
+ add_wait_queue(dentry->d_wait, &wait);
+ do {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ spin_unlock(&dentry->d_lock);
+ schedule();
+ spin_lock(&dentry->d_lock);
+ } while (d_in_lookup(dentry));
+ }
+}
+
+struct dentry *d_alloc_parallel(struct dentry *parent,
+ const struct qstr *name,
+ wait_queue_head_t *wq)
+{
+ unsigned int hash = name->hash;
+ struct hlist_bl_head *b = in_lookup_hash(parent, hash);
+ struct hlist_bl_node *node;
+ struct dentry *new = d_alloc(parent, name);
+ struct dentry *dentry;
+ unsigned seq, r_seq, d_seq;
+
+ if (unlikely(!new))
+ return ERR_PTR(-ENOMEM);
+
+retry:
+ rcu_read_lock();
+ seq = smp_load_acquire(&parent->d_inode->i_dir_seq);
+ r_seq = read_seqbegin(&rename_lock);
+ dentry = __d_lookup_rcu(parent, name, &d_seq);
+ if (unlikely(dentry)) {
+ if (!lockref_get_not_dead(&dentry->d_lockref)) {
+ rcu_read_unlock();
+ goto retry;
+ }
+ if (read_seqcount_retry(&dentry->d_seq, d_seq)) {
+ rcu_read_unlock();
+ dput(dentry);
+ goto retry;
+ }
+ rcu_read_unlock();
+ dput(new);
+ return dentry;
+ }
+ if (unlikely(read_seqretry(&rename_lock, r_seq))) {
+ rcu_read_unlock();
+ goto retry;
+ }
+
+ if (unlikely(seq & 1)) {
+ rcu_read_unlock();
+ goto retry;
+ }
+
+ hlist_bl_lock(b);
+ if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
+ hlist_bl_unlock(b);
+ rcu_read_unlock();
+ goto retry;
+ }
+ /*
+ * No changes for the parent since the beginning of d_lookup().
+ * Since all removals from the chain happen with hlist_bl_lock(),
+ * any potential in-lookup matches are going to stay here until
+ * we unlock the chain. All fields are stable in everything
+ * we encounter.
+ */
+ hlist_bl_for_each_entry(dentry, node, b, d_u.d_in_lookup_hash) {
+ if (dentry->d_name.hash != hash)
+ continue;
+ if (dentry->d_parent != parent)
+ continue;
+ if (!d_same_name(dentry, parent, name))
+ continue;
+ hlist_bl_unlock(b);
+ /* now we can try to grab a reference */
+ if (!lockref_get_not_dead(&dentry->d_lockref)) {
+ rcu_read_unlock();
+ goto retry;
+ }
+
+ rcu_read_unlock();
+ /*
+ * somebody is likely to be still doing lookup for it;
+ * wait for them to finish
+ */
+ spin_lock(&dentry->d_lock);
+ d_wait_lookup(dentry);
+ /*
+ * it's not in-lookup anymore; in principle we should repeat
+ * everything from dcache lookup, but it's likely to be what
+ * d_lookup() would've found anyway. If it is, just return it;
+ * otherwise we really have to repeat the whole thing.
+ */
+ if (unlikely(dentry->d_name.hash != hash))
+ goto mismatch;
+ if (unlikely(dentry->d_parent != parent))
+ goto mismatch;
+ if (unlikely(d_unhashed(dentry)))
+ goto mismatch;
+ if (unlikely(!d_same_name(dentry, parent, name)))
+ goto mismatch;
+ /* OK, it *is* a hashed match; return it */
+ spin_unlock(&dentry->d_lock);
+ dput(new);
+ return dentry;
+ }
+ rcu_read_unlock();
+ /* we can't take ->d_lock here; it's OK, though. */
+ new->d_flags |= DCACHE_PAR_LOOKUP;
+ new->d_wait = wq;
+ hlist_bl_add_head_rcu(&new->d_u.d_in_lookup_hash, b);
+ hlist_bl_unlock(b);
+ return new;
+mismatch:
+ spin_unlock(&dentry->d_lock);
+ dput(dentry);
+ goto retry;
+}
+EXPORT_SYMBOL(d_alloc_parallel);
+
+void __d_lookup_done(struct dentry *dentry)
+{
+ struct hlist_bl_head *b = in_lookup_hash(dentry->d_parent,
+ dentry->d_name.hash);
+ hlist_bl_lock(b);
+ dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
+ __hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
+ wake_up_all(dentry->d_wait);
+ dentry->d_wait = NULL;
+ hlist_bl_unlock(b);
+ INIT_HLIST_NODE(&dentry->d_u.d_alias);
+ INIT_LIST_HEAD(&dentry->d_lru);
+}
+EXPORT_SYMBOL(__d_lookup_done);
+
+/* inode->i_lock held if inode is non-NULL */
+
+static inline void __d_add(struct dentry *dentry, struct inode *inode)
+{
+ struct inode *dir = NULL;
+ unsigned n;
+ spin_lock(&dentry->d_lock);
+ if (unlikely(d_in_lookup(dentry))) {
+ dir = dentry->d_parent->d_inode;
+ n = start_dir_add(dir);
+ __d_lookup_done(dentry);
+ }
+ if (inode) {
+ unsigned add_flags = d_flags_for_inode(inode);
+ hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
+ raw_write_seqcount_begin(&dentry->d_seq);
+ __d_set_inode_and_type(dentry, inode, add_flags);
+ raw_write_seqcount_end(&dentry->d_seq);
+ fsnotify_update_flags(dentry);
+ }
+ __d_rehash(dentry);
+ if (dir)
+ end_dir_add(dir, n);
+ spin_unlock(&dentry->d_lock);
+ if (inode)
+ spin_unlock(&inode->i_lock);
+}
+
+/**
+ * d_add - add dentry to hash queues
+ * @entry: dentry to add
+ * @inode: The inode to attach to this dentry
+ *
+ * This adds the entry to the hash queues and initializes @inode.
+ * The entry was actually filled in earlier during d_alloc().
+ */
+
+void d_add(struct dentry *entry, struct inode *inode)
+{
+ if (inode) {
+ security_d_instantiate(entry, inode);
+ spin_lock(&inode->i_lock);
+ }
+ __d_add(entry, inode);
+}
+EXPORT_SYMBOL(d_add);
+
+/**
+ * d_exact_alias - find and hash an exact unhashed alias
+ * @entry: dentry to add
+ * @inode: The inode to go with this dentry
+ *
+ * If an unhashed dentry with the same name/parent and desired
+ * inode already exists, hash and return it. Otherwise, return
+ * NULL.
+ *
+ * Parent directory should be locked.
+ */
+struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
+{
+ struct dentry *alias;
+ unsigned int hash = entry->d_name.hash;
+
+ spin_lock(&inode->i_lock);
+ hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+ /*
+ * Don't need alias->d_lock here, because aliases with
+ * d_parent == entry->d_parent are not subject to name or
+ * parent changes, because the parent inode i_mutex is held.
+ */
+ if (alias->d_name.hash != hash)
+ continue;
+ if (alias->d_parent != entry->d_parent)
+ continue;
+ if (!d_same_name(alias, entry->d_parent, &entry->d_name))
+ continue;
+ spin_lock(&alias->d_lock);
+ if (!d_unhashed(alias)) {
+ spin_unlock(&alias->d_lock);
+ alias = NULL;
+ } else {
+ __dget_dlock(alias);
+ __d_rehash(alias);
+ spin_unlock(&alias->d_lock);
+ }
+ spin_unlock(&inode->i_lock);
+ return alias;
+ }
+ spin_unlock(&inode->i_lock);
+ return NULL;
+}
+EXPORT_SYMBOL(d_exact_alias);
+
+static void swap_names(struct dentry *dentry, struct dentry *target)
+{
+ if (unlikely(dname_external(target))) {
+ if (unlikely(dname_external(dentry))) {
+ /*
+ * Both external: swap the pointers
+ */
+ swap(target->d_name.name, dentry->d_name.name);
+ } else {
+ /*
+ * dentry:internal, target:external. Steal target's
+ * storage and make target internal.
+ */
+ memcpy(target->d_iname, dentry->d_name.name,
+ dentry->d_name.len + 1);
+ dentry->d_name.name = target->d_name.name;
+ target->d_name.name = target->d_iname;
+ }
+ } else {
+ if (unlikely(dname_external(dentry))) {
+ /*
+ * dentry:external, target:internal. Give dentry's
+ * storage to target and make dentry internal
+ */
+ memcpy(dentry->d_iname, target->d_name.name,
+ target->d_name.len + 1);
+ target->d_name.name = dentry->d_name.name;
+ dentry->d_name.name = dentry->d_iname;
+ } else {
+ /*
+ * Both are internal.
+ */
+ unsigned int i;
+ BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
+ for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
+ swap(((long *) &dentry->d_iname)[i],
+ ((long *) &target->d_iname)[i]);
+ }
+ }
+ }
+ swap(dentry->d_name.hash_len, target->d_name.hash_len);
+}
+
+static void copy_name(struct dentry *dentry, struct dentry *target)
+{
+ struct external_name *old_name = NULL;
+ if (unlikely(dname_external(dentry)))
+ old_name = external_name(dentry);
+ if (unlikely(dname_external(target))) {
+ atomic_inc(&external_name(target)->u.count);
+ dentry->d_name = target->d_name;
+ } else {
+ memcpy(dentry->d_iname, target->d_name.name,
+ target->d_name.len + 1);
+ dentry->d_name.name = dentry->d_iname;
+ dentry->d_name.hash_len = target->d_name.hash_len;
+ }
+ if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
+ call_rcu(&old_name->u.head, __d_free_external_name);
+}
+
+/*
+ * __d_move - move a dentry
+ * @dentry: entry to move
+ * @target: new dentry
+ * @exchange: exchange the two dentries
+ *
+ * Update the dcache to reflect the move of a file name. Negative
+ * dcache entries should not be moved in this way. Caller must hold
+ * rename_lock, the i_mutex of the source and target directories,
+ * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
+ */
+static void __d_move(struct dentry *dentry, struct dentry *target,
+ bool exchange)
+{
+ struct dentry *old_parent, *p;
+ struct inode *dir = NULL;
+ unsigned n;
+
+ WARN_ON(!dentry->d_inode);
+ if (WARN_ON(dentry == target))
+ return;
+
+ BUG_ON(d_ancestor(target, dentry));
+ old_parent = dentry->d_parent;
+ p = d_ancestor(old_parent, target);
+ if (IS_ROOT(dentry)) {
+ BUG_ON(p);
+ spin_lock(&target->d_parent->d_lock);
+ } else if (!p) {
+ /* target is not a descendent of dentry->d_parent */
+ spin_lock(&target->d_parent->d_lock);
+ spin_lock_nested(&old_parent->d_lock, DENTRY_D_LOCK_NESTED);
+ } else {
+ BUG_ON(p == dentry);
+ spin_lock(&old_parent->d_lock);
+ if (p != target)
+ spin_lock_nested(&target->d_parent->d_lock,
+ DENTRY_D_LOCK_NESTED);
+ }
+ spin_lock_nested(&dentry->d_lock, 2);
+ spin_lock_nested(&target->d_lock, 3);
+
+ if (unlikely(d_in_lookup(target))) {
+ dir = target->d_parent->d_inode;
+ n = start_dir_add(dir);
+ __d_lookup_done(target);
+ }
+
+ write_seqcount_begin(&dentry->d_seq);
+ write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
+
+ /* unhash both */
+ if (!d_unhashed(dentry))
+ ___d_drop(dentry);
+ if (!d_unhashed(target))
+ ___d_drop(target);
+
+ /* ... and switch them in the tree */
+ dentry->d_parent = target->d_parent;
+ if (!exchange) {
+ copy_name(dentry, target);
+ target->d_hash.pprev = NULL;
+ dentry->d_parent->d_lockref.count++;
+ if (dentry == old_parent)
+ dentry->d_flags |= DCACHE_RCUACCESS;
+ else
+ WARN_ON(!--old_parent->d_lockref.count);
+ } else {
+ target->d_parent = old_parent;
+ swap_names(dentry, target);
+ list_move(&target->d_child, &target->d_parent->d_subdirs);
+ __d_rehash(target);
+ fsnotify_update_flags(target);
+ }
+ list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
+ __d_rehash(dentry);
+ fsnotify_update_flags(dentry);
+
+ write_seqcount_end(&target->d_seq);
+ write_seqcount_end(&dentry->d_seq);
+
+ if (dir)
+ end_dir_add(dir, n);
+
+ if (dentry->d_parent != old_parent)
+ spin_unlock(&dentry->d_parent->d_lock);
+ if (dentry != old_parent)
+ spin_unlock(&old_parent->d_lock);
+ spin_unlock(&target->d_lock);
+ spin_unlock(&dentry->d_lock);
+}
+
+/*
+ * d_move - move a dentry
+ * @dentry: entry to move
+ * @target: new dentry
+ *
+ * Update the dcache to reflect the move of a file name. Negative
+ * dcache entries should not be moved in this way. See the locking
+ * requirements for __d_move.
+ */
+void d_move(struct dentry *dentry, struct dentry *target)
+{
+ write_seqlock(&rename_lock);
+ __d_move(dentry, target, false);
+ write_sequnlock(&rename_lock);
+}
+EXPORT_SYMBOL(d_move);
+
+/*
+ * d_exchange - exchange two dentries
+ * @dentry1: first dentry
+ * @dentry2: second dentry
+ */
+void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
+{
+ write_seqlock(&rename_lock);
+
+ WARN_ON(!dentry1->d_inode);
+ WARN_ON(!dentry2->d_inode);
+ WARN_ON(IS_ROOT(dentry1));
+ WARN_ON(IS_ROOT(dentry2));
+
+ __d_move(dentry1, dentry2, true);
+
+ write_sequnlock(&rename_lock);
+}
+
+/**
+ * d_ancestor - search for an ancestor
+ * @p1: ancestor dentry
+ * @p2: child dentry
+ *
+ * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
+ * an ancestor of p2, else NULL.
+ */
+struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
+{
+ struct dentry *p;
+
+ for (p = p2; !IS_ROOT(p); p = p->d_parent) {
+ if (p->d_parent == p1)
+ return p;
+ }
+ return NULL;
+}
+
+/*
+ * This helper attempts to cope with remotely renamed directories
+ *
+ * It assumes that the caller is already holding
+ * dentry->d_parent->d_inode->i_mutex, and rename_lock
+ *
+ * Note: If ever the locking in lock_rename() changes, then please
+ * remember to update this too...
+ */
+static int __d_unalias(struct inode *inode,
+ struct dentry *dentry, struct dentry *alias)
+{
+ struct mutex *m1 = NULL;
+ struct rw_semaphore *m2 = NULL;
+ int ret = -ESTALE;
+
+ /* If alias and dentry share a parent, then no extra locks required */
+ if (alias->d_parent == dentry->d_parent)
+ goto out_unalias;
+
+ /* See lock_rename() */
+ if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
+ goto out_err;
+ m1 = &dentry->d_sb->s_vfs_rename_mutex;
+ if (!inode_trylock_shared(alias->d_parent->d_inode))
+ goto out_err;
+ m2 = &alias->d_parent->d_inode->i_rwsem;
+out_unalias:
+ __d_move(alias, dentry, false);
+ ret = 0;
+out_err:
+ if (m2)
+ up_read(m2);
+ if (m1)
+ mutex_unlock(m1);
+ return ret;
+}
+
+/**
+ * d_splice_alias - splice a disconnected dentry into the tree if one exists
+ * @inode: the inode which may have a disconnected dentry
+ * @dentry: a negative dentry which we want to point to the inode.
+ *
+ * If inode is a directory and has an IS_ROOT alias, then d_move that in
+ * place of the given dentry and return it, else simply d_add the inode
+ * to the dentry and return NULL.
+ *
+ * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
+ * we should error out: directories can't have multiple aliases.
+ *
+ * This is needed in the lookup routine of any filesystem that is exportable
+ * (via knfsd) so that we can build dcache paths to directories effectively.
+ *
+ * If a dentry was found and moved, then it is returned. Otherwise NULL
+ * is returned. This matches the expected return value of ->lookup.
+ *
+ * Cluster filesystems may call this function with a negative, hashed dentry.
+ * In that case, we know that the inode will be a regular file, and also this
+ * will only occur during atomic_open. So we need to check for the dentry
+ * being already hashed only in the final case.
+ */
+struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
+{
+ if (IS_ERR(inode))
+ return ERR_CAST(inode);
+
+ BUG_ON(!d_unhashed(dentry));
+
+ if (!inode)
+ goto out;
+
+ security_d_instantiate(dentry, inode);
+ spin_lock(&inode->i_lock);
+ if (S_ISDIR(inode->i_mode)) {
+ struct dentry *new = __d_find_any_alias(inode);
+ if (unlikely(new)) {
+ /* The reference to new ensures it remains an alias */
+ spin_unlock(&inode->i_lock);
+ write_seqlock(&rename_lock);
+ if (unlikely(d_ancestor(new, dentry))) {
+ write_sequnlock(&rename_lock);
+ dput(new);
+ new = ERR_PTR(-ELOOP);
+ pr_warn_ratelimited(
+ "VFS: Lookup of '%s' in %s %s"
+ " would have caused loop\n",
+ dentry->d_name.name,
+ inode->i_sb->s_type->name,
+ inode->i_sb->s_id);
+ } else if (!IS_ROOT(new)) {
+ struct dentry *old_parent = dget(new->d_parent);
+ int err = __d_unalias(inode, dentry, new);
+ write_sequnlock(&rename_lock);
+ if (err) {
+ dput(new);
+ new = ERR_PTR(err);
+ }
+ dput(old_parent);
+ } else {
+ __d_move(new, dentry, false);
+ write_sequnlock(&rename_lock);
+ }
+ iput(inode);
+ return new;
+ }
+ }
+out:
+ __d_add(dentry, inode);
+ return NULL;
+}
+EXPORT_SYMBOL(d_splice_alias);
+
+/*
+ * Test whether new_dentry is a subdirectory of old_dentry.
+ *
+ * Trivially implemented using the dcache structure
+ */
+
+/**
+ * is_subdir - is new dentry a subdirectory of old_dentry
+ * @new_dentry: new dentry
+ * @old_dentry: old dentry
+ *
+ * Returns true if new_dentry is a subdirectory of the parent (at any depth).
+ * Returns false otherwise.
+ * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
+ */
+
+bool is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
+{
+ bool result;
+ unsigned seq;
+
+ if (new_dentry == old_dentry)
+ return true;
+
+ do {
+ /* for restarting inner loop in case of seq retry */
+ seq = read_seqbegin(&rename_lock);
+ /*
+ * Need rcu_readlock to protect against the d_parent trashing
+ * due to d_move
+ */
+ rcu_read_lock();
+ if (d_ancestor(old_dentry, new_dentry))
+ result = true;
+ else
+ result = false;
+ rcu_read_unlock();
+ } while (read_seqretry(&rename_lock, seq));
+
+ return result;
+}
+EXPORT_SYMBOL(is_subdir);
+
+static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
+{
+ struct dentry *root = data;
+ if (dentry != root) {
+ if (d_unhashed(dentry) || !dentry->d_inode)
+ return D_WALK_SKIP;
+
+ if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
+ dentry->d_flags |= DCACHE_GENOCIDE;
+ dentry->d_lockref.count--;
+ }
+ }
+ return D_WALK_CONTINUE;
+}
+
+void d_genocide(struct dentry *parent)
+{
+ d_walk(parent, parent, d_genocide_kill);
+}
+
+EXPORT_SYMBOL(d_genocide);
+
+void d_tmpfile(struct dentry *dentry, struct inode *inode)
+{
+ inode_dec_link_count(inode);
+ BUG_ON(dentry->d_name.name != dentry->d_iname ||
+ !hlist_unhashed(&dentry->d_u.d_alias) ||
+ !d_unlinked(dentry));
+ spin_lock(&dentry->d_parent->d_lock);
+ spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+ dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
+ (unsigned long long)inode->i_ino);
+ spin_unlock(&dentry->d_lock);
+ spin_unlock(&dentry->d_parent->d_lock);
+ d_instantiate(dentry, inode);
+}
+EXPORT_SYMBOL(d_tmpfile);
+
+static __initdata unsigned long dhash_entries;
+static int __init set_dhash_entries(char *str)
+{
+ if (!str)
+ return 0;
+ dhash_entries = simple_strtoul(str, &str, 0);
+ return 1;
+}
+__setup("dhash_entries=", set_dhash_entries);
+
+static void __init dcache_init_early(void)
+{
+ /* If hashes are distributed across NUMA nodes, defer
+ * hash allocation until vmalloc space is available.
+ */
+ if (hashdist)
+ return;
+
+ dentry_hashtable =
+ alloc_large_system_hash("Dentry cache",
+ sizeof(struct hlist_bl_head),
+ dhash_entries,
+ 13,
+ HASH_EARLY | HASH_ZERO,
+ &d_hash_shift,
+ NULL,
+ 0,
+ 0);
+ d_hash_shift = 32 - d_hash_shift;
+}
+
+static void __init dcache_init(void)
+{
+ /*
+ * A constructor could be added for stable state like the lists,
+ * but it is probably not worth it because of the cache nature
+ * of the dcache.
+ */
+ dentry_cache = KMEM_CACHE_USERCOPY(dentry,
+ SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
+ d_iname);
+
+ /* Hash may have been set up in dcache_init_early */
+ if (!hashdist)
+ return;
+
+ dentry_hashtable =
+ alloc_large_system_hash("Dentry cache",
+ sizeof(struct hlist_bl_head),
+ dhash_entries,
+ 13,
+ HASH_ZERO,
+ &d_hash_shift,
+ NULL,
+ 0,
+ 0);
+ d_hash_shift = 32 - d_hash_shift;
+}
+
+/* SLAB cache for __getname() consumers */
+struct kmem_cache *names_cachep __read_mostly;
+EXPORT_SYMBOL(names_cachep);
+
+void __init vfs_caches_init_early(void)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(in_lookup_hashtable); i++)
+ INIT_HLIST_BL_HEAD(&in_lookup_hashtable[i]);
+
+ dcache_init_early();
+ inode_init_early();
+}
+
+void __init vfs_caches_init(void)
+{
+ names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
+ SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL);
+
+ dcache_init();
+ inode_init();
+ files_init();
+ files_maxfiles_init();
+ mnt_init();
+ bdev_cache_init();
+ chrdev_init();
+}