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authorChristian Brauner <brauner@kernel.org>2024-02-18 14:50:13 +0100
committerChristian Brauner <brauner@kernel.org>2024-03-01 12:23:44 +0100
commit07fd7c329839cf0b8c7766883d830a1a0d12d1dd (patch)
treea12a4d6447b3b602d7a8f28019d27d18019c21dd /fs/libfs.c
parentcb12fd8e0dabb9a1c8aef55a6a41e2c255fcdf4b (diff)
libfs: add path_from_stashed()
Add a helper for both nsfs and pidfs to reuse an already stashed dentry or to add and stash a new dentry. Link: https://lore.kernel.org/r/20240218-neufahrzeuge-brauhaus-fb0eb6459771@brauner Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs/libfs.c')
-rw-r--r--fs/libfs.c94
1 files changed, 94 insertions, 0 deletions
diff --git a/fs/libfs.c b/fs/libfs.c
index eec6031b0155..2a55e87e1439 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1973,3 +1973,97 @@ struct timespec64 simple_inode_init_ts(struct inode *inode)
return ts;
}
EXPORT_SYMBOL(simple_inode_init_ts);
+
+static inline struct dentry *get_stashed_dentry(struct dentry *stashed)
+{
+ struct dentry *dentry;
+
+ guard(rcu)();
+ dentry = READ_ONCE(stashed);
+ if (!dentry)
+ return NULL;
+ if (!lockref_get_not_dead(&dentry->d_lockref))
+ return NULL;
+ return dentry;
+}
+
+static struct dentry *stash_dentry(struct dentry **stashed, unsigned long ino,
+ struct super_block *sb,
+ const struct file_operations *fops,
+ void *data)
+{
+ struct dentry *dentry;
+ struct inode *inode;
+
+ dentry = d_alloc_anon(sb);
+ if (!dentry)
+ return ERR_PTR(-ENOMEM);
+
+ inode = new_inode_pseudo(sb);
+ if (!inode) {
+ dput(dentry);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ inode->i_ino = ino;
+ inode->i_flags |= S_IMMUTABLE;
+ inode->i_mode = S_IFREG | S_IRUGO;
+ inode->i_fop = fops;
+ inode->i_private = data;
+ simple_inode_init_ts(inode);
+
+ /* @data is now owned by the fs */
+ d_instantiate(dentry, inode);
+
+ if (cmpxchg(stashed, NULL, dentry)) {
+ d_delete(dentry); /* make sure ->d_prune() does nothing */
+ dput(dentry);
+ cpu_relax();
+ return ERR_PTR(-EAGAIN);
+ }
+
+ return dentry;
+}
+
+/**
+ * path_from_stashed - create path from stashed or new dentry
+ * @stashed: where to retrieve or stash dentry
+ * @ino: inode number to use
+ * @mnt: mnt of the filesystems to use
+ * @fops: file operations to use
+ * @data: data to store in inode->i_private
+ * @path: path to create
+ *
+ * The function tries to retrieve a stashed dentry from @stashed. If the dentry
+ * is still valid then it will be reused. If the dentry isn't able the function
+ * will allocate a new dentry and inode. It will then try to update @stashed
+ * with the newly added dentry. If it fails -EAGAIN is returned and the caller
+ * my retry.
+ *
+ * Special-purpose helper for nsfs and pidfs.
+ *
+ * Return: If 0 or an error is returned the caller can be sure that @data must
+ * be cleaned up. If 1 or -EAGAIN is returned @data is owned by the
+ * filesystem.
+ */
+int path_from_stashed(struct dentry **stashed, unsigned long ino,
+ struct vfsmount *mnt, const struct file_operations *fops,
+ void *data, struct path *path)
+{
+ struct dentry *dentry;
+ int ret = 0;
+
+ dentry = get_stashed_dentry(*stashed);
+ if (dentry)
+ goto out_path;
+
+ dentry = stash_dentry(stashed, ino, mnt->mnt_sb, fops, data);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+ ret = 1;
+
+out_path:
+ path->dentry = dentry;
+ path->mnt = mntget(mnt);
+ return ret;
+}