Unverified Commit 07fd7c32 authored by Christian Brauner's avatar Christian Brauner
Browse files

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: default avatarChristian Brauner <brauner@kernel.org>
parent cb12fd8e

fs/internal.h

+3 −0
Original line number Diff line number Diff line
@@ -310,3 +310,6 @@ ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *po 
struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns);

struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap);

void mnt_idmap_put(struct mnt_idmap *idmap);

int path_from_stashed(struct dentry **stashed, unsigned long ino,

		      struct vfsmount *mnt, const struct file_operations *fops,

		      void *data, struct path *path);

fs/libfs.c

+94 −0
Original line number Diff line number Diff line
@@ -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;

}