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VFS/knfsd: Teach dentry_create() to use atomic_open()

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While knfsd offers combined exclusive create and open results to clients,
on some filesystems those results may not be atomic.  This behavior can be
observed.  For example, an open O_CREAT with mode 0 will succeed in creating
the file but unexpectedly return -EACCES from vfs_open().

Additionally reducing the number of remote RPC calls required for O_CREAT
on network filesystem provides a performance benefit in the open path.

Teach knfsd's helper dentry_create() to use atomic_open() for filesystems
that support it.  The previously const @path is passed up to atomic_open()
and may be modified depending on whether an existing entry was found or if
the atomic_open() returned an error and consumed the passed-in dentry.

Signed-off-by: Benjamin Coddington <bcodding@hammerspace.com>
Link: https://patch.msgid.link/8e449bfb64ab055abb9fd82641a171531415a88c.1764259052.git.bcodding@hammerspace.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Benjamin Coddington 2025-11-27 11:02:05 -05:00 committed by Christian Brauner
parent 36411554e8
commit 64a989dbd1
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
3 changed files with 51 additions and 17 deletions
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55
fs/namei.c
View File

@ -4953,25 +4953,54 @@ EXPORT_SYMBOL(start_creating_user_path);
* On success, returns a "struct file *". Otherwise a ERR_PTR
* is returned.
*/
struct file *dentry_create(const struct path *path, int flags, umode_t mode,
struct file *dentry_create(struct path *path, int flags, umode_t mode,
const struct cred *cred)
{
struct file *f;
int error;
struct file *file __free(fput) = NULL;
struct dentry *dentry = path->dentry;
struct dentry *dir = dentry->d_parent;
struct inode *dir_inode = d_inode(dir);
struct mnt_idmap *idmap;
int error, create_error;
f = alloc_empty_file(flags, cred);
if (IS_ERR(f))
return f;
file = alloc_empty_file(flags, cred);
if (IS_ERR(file))
return file;
error = vfs_create(mnt_idmap(path->mnt), path->dentry, mode, NULL);
if (!error)
error = vfs_open(path, f);
idmap = mnt_idmap(path->mnt);
if (unlikely(error)) {
fput(f);
return ERR_PTR(error);
if (dir_inode->i_op->atomic_open) {
path->dentry = dir;
mode = vfs_prepare_mode(idmap, dir_inode, mode, S_IALLUGO, S_IFREG);
create_error = may_o_create(idmap, path, dentry, mode);
if (create_error)
flags &= ~O_CREAT;
dentry = atomic_open(path, dentry, file, flags, mode);
error = PTR_ERR_OR_ZERO(dentry);
if (unlikely(create_error) && error == -ENOENT)
error = create_error;
if (!error) {
if (file->f_mode & FMODE_CREATED)
fsnotify_create(dir->d_inode, dentry);
if (file->f_mode & FMODE_OPENED)
fsnotify_open(file);
}
path->dentry = dentry;
} else {
error = vfs_create(mnt_idmap(path->mnt), path->dentry, mode, NULL);
if (!error)
error = vfs_open(path, file);
}
return f;
if (unlikely(error))
return ERR_PTR(error);
return no_free_ptr(file);
}
EXPORT_SYMBOL(dentry_create);

11
fs/nfsd/nfs4proc.c
View File

@ -194,7 +194,7 @@ static inline bool nfsd4_create_is_exclusive(int createmode)
}
static __be32
nfsd4_vfs_create(struct svc_fh *fhp, struct dentry *child,
nfsd4_vfs_create(struct svc_fh *fhp, struct dentry **child,
struct nfsd4_open *open)
{
struct file *filp;
@ -202,6 +202,9 @@ nfsd4_vfs_create(struct svc_fh *fhp, struct dentry *child,
int oflags;
oflags = O_CREAT | O_LARGEFILE;
if (nfsd4_create_is_exclusive(open->op_createmode))
oflags |= O_EXCL;
switch (open->op_share_access & NFS4_SHARE_ACCESS_BOTH) {
case NFS4_SHARE_ACCESS_WRITE:
oflags |= O_WRONLY;
@ -214,9 +217,11 @@ nfsd4_vfs_create(struct svc_fh *fhp, struct dentry *child,
}
path.mnt = fhp->fh_export->ex_path.mnt;
path.dentry = child;
path.dentry = *child;
filp = dentry_create(&path, oflags, open->op_iattr.ia_mode,
current_cred());
*child = path.dentry;
if (IS_ERR(filp))
return nfserrno(PTR_ERR(filp));
@ -350,7 +355,7 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
status = fh_fill_pre_attrs(fhp);
if (status != nfs_ok)
goto out;
status = nfsd4_vfs_create(fhp, child, open);
status = nfsd4_vfs_create(fhp, &child, open);
if (status != nfs_ok)
goto out;
open->op_created = true;

2
include/linux/fs.h
View File

@ -2457,7 +2457,7 @@ struct file *dentry_open(const struct path *path, int flags,
const struct cred *creds);
struct file *dentry_open_nonotify(const struct path *path, int flags,
const struct cred *cred);
struct file *dentry_create(const struct path *path, int flags, umode_t mode,
struct file *dentry_create(struct path *path, int flags, umode_t mode,
const struct cred *cred);
const struct path *backing_file_user_path(const struct file *f);