v4.19.13 snapshot.
diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
new file mode 100644
index 0000000..305b220
--- /dev/null
+++ b/fs/kernfs/symlink.c
@@ -0,0 +1,151 @@
+/*
+ * fs/kernfs/symlink.c - kernfs symlink implementation
+ *
+ * Copyright (c) 2001-3 Patrick Mochel
+ * Copyright (c) 2007 SUSE Linux Products GmbH
+ * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
+ *
+ * This file is released under the GPLv2.
+ */
+
+#include <linux/fs.h>
+#include <linux/gfp.h>
+#include <linux/namei.h>
+
+#include "kernfs-internal.h"
+
+/**
+ * kernfs_create_link - create a symlink
+ * @parent: directory to create the symlink in
+ * @name: name of the symlink
+ * @target: target node for the symlink to point to
+ *
+ * Returns the created node on success, ERR_PTR() value on error.
+ * Ownership of the link matches ownership of the target.
+ */
+struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
+ const char *name,
+ struct kernfs_node *target)
+{
+ struct kernfs_node *kn;
+ int error;
+ kuid_t uid = GLOBAL_ROOT_UID;
+ kgid_t gid = GLOBAL_ROOT_GID;
+
+ if (target->iattr) {
+ uid = target->iattr->ia_iattr.ia_uid;
+ gid = target->iattr->ia_iattr.ia_gid;
+ }
+
+ kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, uid, gid,
+ KERNFS_LINK);
+ if (!kn)
+ return ERR_PTR(-ENOMEM);
+
+ if (kernfs_ns_enabled(parent))
+ kn->ns = target->ns;
+ kn->symlink.target_kn = target;
+ kernfs_get(target); /* ref owned by symlink */
+
+ error = kernfs_add_one(kn);
+ if (!error)
+ return kn;
+
+ kernfs_put(kn);
+ return ERR_PTR(error);
+}
+
+static int kernfs_get_target_path(struct kernfs_node *parent,
+ struct kernfs_node *target, char *path)
+{
+ struct kernfs_node *base, *kn;
+ char *s = path;
+ int len = 0;
+
+ /* go up to the root, stop at the base */
+ base = parent;
+ while (base->parent) {
+ kn = target->parent;
+ while (kn->parent && base != kn)
+ kn = kn->parent;
+
+ if (base == kn)
+ break;
+
+ strcpy(s, "../");
+ s += 3;
+ base = base->parent;
+ }
+
+ /* determine end of target string for reverse fillup */
+ kn = target;
+ while (kn->parent && kn != base) {
+ len += strlen(kn->name) + 1;
+ kn = kn->parent;
+ }
+
+ /* check limits */
+ if (len < 2)
+ return -EINVAL;
+ len--;
+ if ((s - path) + len > PATH_MAX)
+ return -ENAMETOOLONG;
+
+ /* reverse fillup of target string from target to base */
+ kn = target;
+ while (kn->parent && kn != base) {
+ int slen = strlen(kn->name);
+
+ len -= slen;
+ memcpy(s + len, kn->name, slen);
+ if (len)
+ s[--len] = '/';
+
+ kn = kn->parent;
+ }
+
+ return 0;
+}
+
+static int kernfs_getlink(struct inode *inode, char *path)
+{
+ struct kernfs_node *kn = inode->i_private;
+ struct kernfs_node *parent = kn->parent;
+ struct kernfs_node *target = kn->symlink.target_kn;
+ int error;
+
+ mutex_lock(&kernfs_mutex);
+ error = kernfs_get_target_path(parent, target, path);
+ mutex_unlock(&kernfs_mutex);
+
+ return error;
+}
+
+static const char *kernfs_iop_get_link(struct dentry *dentry,
+ struct inode *inode,
+ struct delayed_call *done)
+{
+ char *body;
+ int error;
+
+ if (!dentry)
+ return ERR_PTR(-ECHILD);
+ body = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!body)
+ return ERR_PTR(-ENOMEM);
+ error = kernfs_getlink(inode, body);
+ if (unlikely(error < 0)) {
+ kfree(body);
+ return ERR_PTR(error);
+ }
+ set_delayed_call(done, kfree_link, body);
+ return body;
+}
+
+const struct inode_operations kernfs_symlink_iops = {
+ .listxattr = kernfs_iop_listxattr,
+ .get_link = kernfs_iop_get_link,
+ .setattr = kernfs_iop_setattr,
+ .getattr = kernfs_iop_getattr,
+ .permission = kernfs_iop_permission,
+};