v4.19.13 snapshot.
diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
new file mode 100644
index 0000000..f776807
--- /dev/null
+++ b/drivers/base/devtmpfs.c
@@ -0,0 +1,446 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * devtmpfs - kernel-maintained tmpfs-based /dev
+ *
+ * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
+ *
+ * During bootup, before any driver core device is registered,
+ * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
+ * device which requests a device node, will add a node in this
+ * filesystem.
+ * By default, all devices are named after the name of the device,
+ * owned by root and have a default mode of 0600. Subsystems can
+ * overwrite the default setting if needed.
+ */
+
+#include <linux/kernel.h>
+#include <linux/syscalls.h>
+#include <linux/mount.h>
+#include <linux/device.h>
+#include <linux/genhd.h>
+#include <linux/namei.h>
+#include <linux/fs.h>
+#include <linux/shmem_fs.h>
+#include <linux/ramfs.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/kthread.h>
+#include "base.h"
+
+static struct task_struct *thread;
+
+#if defined CONFIG_DEVTMPFS_MOUNT
+static int mount_dev = 1;
+#else
+static int mount_dev;
+#endif
+
+static DEFINE_SPINLOCK(req_lock);
+
+static struct req {
+ struct req *next;
+ struct completion done;
+ int err;
+ const char *name;
+ umode_t mode; /* 0 => delete */
+ kuid_t uid;
+ kgid_t gid;
+ struct device *dev;
+} *requests;
+
+static int __init mount_param(char *str)
+{
+ mount_dev = simple_strtoul(str, NULL, 0);
+ return 1;
+}
+__setup("devtmpfs.mount=", mount_param);
+
+static struct dentry *dev_mount(struct file_system_type *fs_type, int flags,
+ const char *dev_name, void *data)
+{
+#ifdef CONFIG_TMPFS
+ return mount_single(fs_type, flags, data, shmem_fill_super);
+#else
+ return mount_single(fs_type, flags, data, ramfs_fill_super);
+#endif
+}
+
+static struct file_system_type dev_fs_type = {
+ .name = "devtmpfs",
+ .mount = dev_mount,
+ .kill_sb = kill_litter_super,
+};
+
+#ifdef CONFIG_BLOCK
+static inline int is_blockdev(struct device *dev)
+{
+ return dev->class == &block_class;
+}
+#else
+static inline int is_blockdev(struct device *dev) { return 0; }
+#endif
+
+int devtmpfs_create_node(struct device *dev)
+{
+ const char *tmp = NULL;
+ struct req req;
+
+ if (!thread)
+ return 0;
+
+ req.mode = 0;
+ req.uid = GLOBAL_ROOT_UID;
+ req.gid = GLOBAL_ROOT_GID;
+ req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
+ if (!req.name)
+ return -ENOMEM;
+
+ if (req.mode == 0)
+ req.mode = 0600;
+ if (is_blockdev(dev))
+ req.mode |= S_IFBLK;
+ else
+ req.mode |= S_IFCHR;
+
+ req.dev = dev;
+
+ init_completion(&req.done);
+
+ spin_lock(&req_lock);
+ req.next = requests;
+ requests = &req;
+ spin_unlock(&req_lock);
+
+ wake_up_process(thread);
+ wait_for_completion(&req.done);
+
+ kfree(tmp);
+
+ return req.err;
+}
+
+int devtmpfs_delete_node(struct device *dev)
+{
+ const char *tmp = NULL;
+ struct req req;
+
+ if (!thread)
+ return 0;
+
+ req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
+ if (!req.name)
+ return -ENOMEM;
+
+ req.mode = 0;
+ req.dev = dev;
+
+ init_completion(&req.done);
+
+ spin_lock(&req_lock);
+ req.next = requests;
+ requests = &req;
+ spin_unlock(&req_lock);
+
+ wake_up_process(thread);
+ wait_for_completion(&req.done);
+
+ kfree(tmp);
+ return req.err;
+}
+
+static int dev_mkdir(const char *name, umode_t mode)
+{
+ struct dentry *dentry;
+ struct path path;
+ int err;
+
+ dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+
+ err = vfs_mkdir(d_inode(path.dentry), dentry, mode);
+ if (!err)
+ /* mark as kernel-created inode */
+ d_inode(dentry)->i_private = &thread;
+ done_path_create(&path, dentry);
+ return err;
+}
+
+static int create_path(const char *nodepath)
+{
+ char *path;
+ char *s;
+ int err = 0;
+
+ /* parent directories do not exist, create them */
+ path = kstrdup(nodepath, GFP_KERNEL);
+ if (!path)
+ return -ENOMEM;
+
+ s = path;
+ for (;;) {
+ s = strchr(s, '/');
+ if (!s)
+ break;
+ s[0] = '\0';
+ err = dev_mkdir(path, 0755);
+ if (err && err != -EEXIST)
+ break;
+ s[0] = '/';
+ s++;
+ }
+ kfree(path);
+ return err;
+}
+
+static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
+ kgid_t gid, struct device *dev)
+{
+ struct dentry *dentry;
+ struct path path;
+ int err;
+
+ dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
+ if (dentry == ERR_PTR(-ENOENT)) {
+ create_path(nodename);
+ dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
+ }
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+
+ err = vfs_mknod(d_inode(path.dentry), dentry, mode, dev->devt);
+ if (!err) {
+ struct iattr newattrs;
+
+ newattrs.ia_mode = mode;
+ newattrs.ia_uid = uid;
+ newattrs.ia_gid = gid;
+ newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
+ inode_lock(d_inode(dentry));
+ notify_change(dentry, &newattrs, NULL);
+ inode_unlock(d_inode(dentry));
+
+ /* mark as kernel-created inode */
+ d_inode(dentry)->i_private = &thread;
+ }
+ done_path_create(&path, dentry);
+ return err;
+}
+
+static int dev_rmdir(const char *name)
+{
+ struct path parent;
+ struct dentry *dentry;
+ int err;
+
+ dentry = kern_path_locked(name, &parent);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+ if (d_really_is_positive(dentry)) {
+ if (d_inode(dentry)->i_private == &thread)
+ err = vfs_rmdir(d_inode(parent.dentry), dentry);
+ else
+ err = -EPERM;
+ } else {
+ err = -ENOENT;
+ }
+ dput(dentry);
+ inode_unlock(d_inode(parent.dentry));
+ path_put(&parent);
+ return err;
+}
+
+static int delete_path(const char *nodepath)
+{
+ const char *path;
+ int err = 0;
+
+ path = kstrdup(nodepath, GFP_KERNEL);
+ if (!path)
+ return -ENOMEM;
+
+ for (;;) {
+ char *base;
+
+ base = strrchr(path, '/');
+ if (!base)
+ break;
+ base[0] = '\0';
+ err = dev_rmdir(path);
+ if (err)
+ break;
+ }
+
+ kfree(path);
+ return err;
+}
+
+static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
+{
+ /* did we create it */
+ if (inode->i_private != &thread)
+ return 0;
+
+ /* does the dev_t match */
+ if (is_blockdev(dev)) {
+ if (!S_ISBLK(stat->mode))
+ return 0;
+ } else {
+ if (!S_ISCHR(stat->mode))
+ return 0;
+ }
+ if (stat->rdev != dev->devt)
+ return 0;
+
+ /* ours */
+ return 1;
+}
+
+static int handle_remove(const char *nodename, struct device *dev)
+{
+ struct path parent;
+ struct dentry *dentry;
+ int deleted = 0;
+ int err;
+
+ dentry = kern_path_locked(nodename, &parent);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+
+ if (d_really_is_positive(dentry)) {
+ struct kstat stat;
+ struct path p = {.mnt = parent.mnt, .dentry = dentry};
+ err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
+ AT_STATX_SYNC_AS_STAT);
+ if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
+ struct iattr newattrs;
+ /*
+ * before unlinking this node, reset permissions
+ * of possible references like hardlinks
+ */
+ newattrs.ia_uid = GLOBAL_ROOT_UID;
+ newattrs.ia_gid = GLOBAL_ROOT_GID;
+ newattrs.ia_mode = stat.mode & ~0777;
+ newattrs.ia_valid =
+ ATTR_UID|ATTR_GID|ATTR_MODE;
+ inode_lock(d_inode(dentry));
+ notify_change(dentry, &newattrs, NULL);
+ inode_unlock(d_inode(dentry));
+ err = vfs_unlink(d_inode(parent.dentry), dentry, NULL);
+ if (!err || err == -ENOENT)
+ deleted = 1;
+ }
+ } else {
+ err = -ENOENT;
+ }
+ dput(dentry);
+ inode_unlock(d_inode(parent.dentry));
+
+ path_put(&parent);
+ if (deleted && strchr(nodename, '/'))
+ delete_path(nodename);
+ return err;
+}
+
+/*
+ * If configured, or requested by the commandline, devtmpfs will be
+ * auto-mounted after the kernel mounted the root filesystem.
+ */
+int devtmpfs_mount(const char *mntdir)
+{
+ int err;
+
+ if (!mount_dev)
+ return 0;
+
+ if (!thread)
+ return 0;
+
+ err = ksys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT,
+ NULL);
+ if (err)
+ printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
+ else
+ printk(KERN_INFO "devtmpfs: mounted\n");
+ return err;
+}
+
+static DECLARE_COMPLETION(setup_done);
+
+static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
+ struct device *dev)
+{
+ if (mode)
+ return handle_create(name, mode, uid, gid, dev);
+ else
+ return handle_remove(name, dev);
+}
+
+static int devtmpfsd(void *p)
+{
+ char options[] = "mode=0755";
+ int *err = p;
+ *err = ksys_unshare(CLONE_NEWNS);
+ if (*err)
+ goto out;
+ *err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
+ if (*err)
+ goto out;
+ ksys_chdir("/.."); /* will traverse into overmounted root */
+ ksys_chroot(".");
+ complete(&setup_done);
+ while (1) {
+ spin_lock(&req_lock);
+ while (requests) {
+ struct req *req = requests;
+ requests = NULL;
+ spin_unlock(&req_lock);
+ while (req) {
+ struct req *next = req->next;
+ req->err = handle(req->name, req->mode,
+ req->uid, req->gid, req->dev);
+ complete(&req->done);
+ req = next;
+ }
+ spin_lock(&req_lock);
+ }
+ __set_current_state(TASK_INTERRUPTIBLE);
+ spin_unlock(&req_lock);
+ schedule();
+ }
+ return 0;
+out:
+ complete(&setup_done);
+ return *err;
+}
+
+/*
+ * Create devtmpfs instance, driver-core devices will add their device
+ * nodes here.
+ */
+int __init devtmpfs_init(void)
+{
+ int err = register_filesystem(&dev_fs_type);
+ if (err) {
+ printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
+ "type %i\n", err);
+ return err;
+ }
+
+ thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
+ if (!IS_ERR(thread)) {
+ wait_for_completion(&setup_done);
+ } else {
+ err = PTR_ERR(thread);
+ thread = NULL;
+ }
+
+ if (err) {
+ printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
+ unregister_filesystem(&dev_fs_type);
+ return err;
+ }
+
+ printk(KERN_INFO "devtmpfs: initialized\n");
+ return 0;
+}