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linux/fs/ufs/namei.c
NeilBrown 88d5baf690
Change inode_operations.mkdir to return struct dentry * 
Some filesystems, such as NFS, cifs, ceph, and fuse, do not have
complete control of sequencing on the actual filesystem (e.g.  on a
different server) and may find that the inode created for a mkdir
request already exists in the icache and dcache by the time the mkdir
request returns.  For example, if the filesystem is mounted twice the
directory could be visible on the other mount before it is on the
original mount, and a pair of name_to_handle_at(), open_by_handle_at()
calls could instantiate the directory inode with an IS_ROOT() dentry
before the first mkdir returns.

This means that the dentry passed to ->mkdir() may not be the one that
is associated with the inode after the ->mkdir() completes.  Some
callers need to interact with the inode after the ->mkdir completes and
they currently need to perform a lookup in the (rare) case that the
dentry is no longer hashed.

This lookup-after-mkdir requires that the directory remains locked to
avoid races.  Planned future patches to lock the dentry rather than the
directory will mean that this lookup cannot be performed atomically with
the mkdir.

To remove this barrier, this patch changes ->mkdir to return the
resulting dentry if it is different from the one passed in.
Possible returns are:
  NULL - the directory was created and no other dentry was used
  ERR_PTR() - an error occurred
  non-NULL - this other dentry was spliced in

This patch only changes file-systems to return "ERR_PTR(err)" instead of
"err" or equivalent transformations.  Subsequent patches will make
further changes to some file-systems to return a correct dentry.

Not all filesystems reliably result in a positive hashed dentry:

- NFS, cifs, hostfs will sometimes need to perform a lookup of
  the name to get inode information.  Races could result in this
  returning something different. Note that this lookup is
  non-atomic which is what we are trying to avoid.  Placing the
  lookup in filesystem code means it only happens when the filesystem
  has no other option.
- kernfs and tracefs leave the dentry negative and the ->revalidate
  operation ensures that lookup will be called to correctly populate
  the dentry.  This could be fixed but I don't think it is important
  to any of the users of vfs_mkdir() which look at the dentry.

The recommendation to use
    d_drop();d_splice_alias()
is ugly but fits with current practice.  A planned future patch will
change this.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/20250227013949.536172-2-neilb@suse.de
Signed-off-by: Christian Brauner <brauner@kernel.org>
2025-02-27 20:00:17 +01:00

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// SPDX-License-Identifier: GPL-2.0
/*
* linux/fs/ufs/namei.c
*
* Migration to usage of "page cache" on May 2006 by
* Evgeniy Dushistov <dushistov@mail.ru> based on ext2 code base.
*
* Copyright (C) 1998
* Daniel Pirkl <daniel.pirkl@email.cz>
* Charles University, Faculty of Mathematics and Physics
*
* from
*
* linux/fs/ext2/namei.c
*
* Copyright (C) 1992, 1993, 1994, 1995
* Remy Card (card@masi.ibp.fr)
* Laboratoire MASI - Institut Blaise Pascal
* Universite Pierre et Marie Curie (Paris VI)
*
* from
*
* linux/fs/minix/namei.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* Big-endian to little-endian byte-swapping/bitmaps by
* David S. Miller (davem@caip.rutgers.edu), 1995
*/
#include <linux/time.h>
#include <linux/fs.h>
#include "ufs_fs.h"
#include "ufs.h"
#include "util.h"
static inline int ufs_add_nondir(struct dentry *dentry, struct inode *inode)
{
int err = ufs_add_link(dentry, inode);
if (!err) {
d_instantiate_new(dentry, inode);
return 0;
}
inode_dec_link_count(inode);
discard_new_inode(inode);
return err;
}
static struct dentry *ufs_lookup(struct inode * dir, struct dentry *dentry, unsigned int flags)
{
struct inode * inode = NULL;
ino_t ino;
if (dentry->d_name.len > UFS_MAXNAMLEN)
return ERR_PTR(-ENAMETOOLONG);
ino = ufs_inode_by_name(dir, &dentry->d_name);
if (ino)
inode = ufs_iget(dir->i_sb, ino);
return d_splice_alias(inode, dentry);
}
/*
* By the time this is called, we already have created
* the directory cache entry for the new file, but it
* is so far negative - it has no inode.
*
* If the create succeeds, we fill in the inode information
* with d_instantiate().
*/
static int ufs_create (struct mnt_idmap * idmap,
struct inode * dir, struct dentry * dentry, umode_t mode,
bool excl)
{
struct inode *inode;
inode = ufs_new_inode(dir, mode);
if (IS_ERR(inode))
return PTR_ERR(inode);
inode->i_op = &ufs_file_inode_operations;
inode->i_fop = &ufs_file_operations;
inode->i_mapping->a_ops = &ufs_aops;
mark_inode_dirty(inode);
return ufs_add_nondir(dentry, inode);
}
static int ufs_mknod(struct mnt_idmap *idmap, struct inode *dir,
struct dentry *dentry, umode_t mode, dev_t rdev)
{
struct inode *inode;
int err;
if (!old_valid_dev(rdev))
return -EINVAL;
inode = ufs_new_inode(dir, mode);
err = PTR_ERR(inode);
if (!IS_ERR(inode)) {
init_special_inode(inode, mode, rdev);
ufs_set_inode_dev(inode->i_sb, UFS_I(inode), rdev);
mark_inode_dirty(inode);
err = ufs_add_nondir(dentry, inode);
}
return err;
}
static int ufs_symlink (struct mnt_idmap * idmap, struct inode * dir,
struct dentry * dentry, const char * symname)
{
struct super_block * sb = dir->i_sb;
int err;
unsigned l = strlen(symname)+1;
struct inode * inode;
if (l > sb->s_blocksize)
return -ENAMETOOLONG;
inode = ufs_new_inode(dir, S_IFLNK | S_IRWXUGO);
err = PTR_ERR(inode);
if (IS_ERR(inode))
return err;
if (l > UFS_SB(sb)->s_uspi->s_maxsymlinklen) {
/* slow symlink */
inode->i_op = &page_symlink_inode_operations;
inode_nohighmem(inode);
inode->i_mapping->a_ops = &ufs_aops;
err = page_symlink(inode, symname, l);
if (err)
goto out_fail;
} else {
/* fast symlink */
inode->i_op = &simple_symlink_inode_operations;
inode->i_link = (char *)UFS_I(inode)->i_u1.i_symlink;
memcpy(inode->i_link, symname, l);
inode->i_size = l-1;
}
mark_inode_dirty(inode);
return ufs_add_nondir(dentry, inode);
out_fail:
inode_dec_link_count(inode);
discard_new_inode(inode);
return err;
}
static int ufs_link (struct dentry * old_dentry, struct inode * dir,
struct dentry *dentry)
{
struct inode *inode = d_inode(old_dentry);
int error;
inode_set_ctime_current(inode);
inode_inc_link_count(inode);
ihold(inode);
error = ufs_add_link(dentry, inode);
if (error) {
inode_dec_link_count(inode);
iput(inode);
} else
d_instantiate(dentry, inode);
return error;
}
static struct dentry *ufs_mkdir(struct mnt_idmap * idmap, struct inode * dir,
struct dentry * dentry, umode_t mode)
{
struct inode * inode;
int err;
inode_inc_link_count(dir);
inode = ufs_new_inode(dir, S_IFDIR|mode);
err = PTR_ERR(inode);
if (IS_ERR(inode))
goto out_dir;
inode->i_op = &ufs_dir_inode_operations;
inode->i_fop = &ufs_dir_operations;
inode->i_mapping->a_ops = &ufs_aops;
inode_inc_link_count(inode);
err = ufs_make_empty(inode, dir);
if (err)
goto out_fail;
err = ufs_add_link(dentry, inode);
if (err)
goto out_fail;
d_instantiate_new(dentry, inode);
return NULL;
out_fail:
inode_dec_link_count(inode);
inode_dec_link_count(inode);
discard_new_inode(inode);
out_dir:
inode_dec_link_count(dir);
return ERR_PTR(err);
}
static int ufs_unlink(struct inode *dir, struct dentry *dentry)
{
struct inode * inode = d_inode(dentry);
struct ufs_dir_entry *de;
struct folio *folio;
int err;
de = ufs_find_entry(dir, &dentry->d_name, &folio);
if (!de)
return -ENOENT;
err = ufs_delete_entry(dir, de, folio);
if (!err) {
inode_set_ctime_to_ts(inode, inode_get_ctime(dir));
inode_dec_link_count(inode);
}
folio_release_kmap(folio, de);
return err;
}
static int ufs_rmdir (struct inode * dir, struct dentry *dentry)
{
struct inode * inode = d_inode(dentry);
int err= -ENOTEMPTY;
if (ufs_empty_dir (inode)) {
err = ufs_unlink(dir, dentry);
if (!err) {
inode->i_size = 0;
inode_dec_link_count(inode);
inode_dec_link_count(dir);
}
}
return err;
}
static int ufs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
struct dentry *old_dentry, struct inode *new_dir,
struct dentry *new_dentry, unsigned int flags)
{
struct inode *old_inode = d_inode(old_dentry);
struct inode *new_inode = d_inode(new_dentry);
struct folio *dir_folio = NULL;
struct ufs_dir_entry * dir_de = NULL;
struct folio *old_folio;
struct ufs_dir_entry *old_de;
int err;
if (flags & ~RENAME_NOREPLACE)
return -EINVAL;
old_de = ufs_find_entry(old_dir, &old_dentry->d_name, &old_folio);
if (!old_de)
return -ENOENT;
if (S_ISDIR(old_inode->i_mode)) {
err = -EIO;
dir_de = ufs_dotdot(old_inode, &dir_folio);
if (!dir_de)
goto out_old;
}
if (new_inode) {
struct folio *new_folio;
struct ufs_dir_entry *new_de;
err = -ENOTEMPTY;
if (dir_de && !ufs_empty_dir(new_inode))
goto out_dir;
err = -ENOENT;
new_de = ufs_find_entry(new_dir, &new_dentry->d_name, &new_folio);
if (!new_de)
goto out_dir;
err = ufs_set_link(new_dir, new_de, new_folio, old_inode, 1);
folio_release_kmap(new_folio, new_de);
if (err)
goto out_dir;
inode_set_ctime_current(new_inode);
if (dir_de)
drop_nlink(new_inode);
inode_dec_link_count(new_inode);
} else {
err = ufs_add_link(new_dentry, old_inode);
if (err)
goto out_dir;
if (dir_de)
inode_inc_link_count(new_dir);
}
/*
* Like most other Unix systems, set the ctime for inodes on a
* rename.
*/
inode_set_ctime_current(old_inode);
mark_inode_dirty(old_inode);
err = ufs_delete_entry(old_dir, old_de, old_folio);
if (!err && dir_de) {
if (old_dir != new_dir)
err = ufs_set_link(old_inode, dir_de, dir_folio,
new_dir, 0);
inode_dec_link_count(old_dir);
}
out_dir:
if (dir_de)
folio_release_kmap(dir_folio, dir_de);
out_old:
folio_release_kmap(old_folio, old_de);
return err;
}
const struct inode_operations ufs_dir_inode_operations = {
.create = ufs_create,
.lookup = ufs_lookup,
.link = ufs_link,
.unlink = ufs_unlink,
.symlink = ufs_symlink,
.mkdir = ufs_mkdir,
.rmdir = ufs_rmdir,
.mknod = ufs_mknod,
.rename = ufs_rename,
};
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