With two clients with NFSv3 mounts of the same directory, the sequence:
client1 client2
ls -l afile
echo hello there > afile
echo HELLO > afile
cat afile
will show
HELLO
there
because the O_TRUNC requested in the final 'echo' doesn't take effect.
This is because the "Negative dentry, just create a file" section in
lookup_open() assumes that the file *does* get created since the dentry
was negative, so it sets FMODE_CREATED, and this causes do_open() to
clear O_TRUNC and so the file doesn't get truncated.
Even mounting with -o lookupcache=none does not help as
nfs_neg_need_reval() always returns false if LOOKUP_CREATE is set.
This patch fixes the problem by providing an atomic_open inode operation
for NFSv3 (and v2). The code is largely the code from the branch in
lookup_open() when atomic_open is not provided. The significant change
is that the O_TRUNC flag is passed a new nfs_do_create() which add
'trunc' handling to nfs_create().
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
This is the first time I seriously looked at the atomic_lookup interface
so I might have done something silly. Please expect to find something
wrong :-)
I've only done basic testing so far. I plan to run some test suites
tomorrow, but thought I would post now to get initial feedback.
Thanks.
fs/nfs/dir.c | 55 ++++++++++++++++++++++++++++++++++++++++--
fs/nfs/nfs3proc.c | 1 +
fs/nfs/proc.c | 1 +
include/linux/nfs_fs.h | 3 +++
4 files changed, 58 insertions(+), 2 deletions(-)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index ac505671efbd..48a3a3455f00 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -56,6 +56,8 @@ static int nfs_readdir(struct file *, struct dir_context *);
static int nfs_fsync_dir(struct file *, loff_t, loff_t, int);
static loff_t nfs_llseek_dir(struct file *, loff_t, int);
static void nfs_readdir_clear_array(struct folio *);
+static int nfs_do_create(struct mnt_idmap *idmap, struct inode *dir,
+ struct dentry *dentry, umode_t mode, bool excl, bool trunc);
const struct file_operations nfs_dir_operations = {
.llseek = nfs_llseek_dir,
@@ -2243,6 +2245,45 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags)
#endif /* CONFIG_NFSV4 */
+int nfs_atomic_open_v23(struct inode *dir, struct dentry *dentry,
+ struct file *file, unsigned int open_flags,
+ umode_t mode)
+{
+
+ /* Same as look+open from lookup_open(), but we different O_TRUNC
+ * handling.
+ */
+ int error = 0;
+ unsigned int lookup_flags = 0;
+
+ if (open_flags & O_DIRECTORY)
+ lookup_flags = LOOKUP_OPEN | LOOKUP_DIRECTORY;
+ if (open_flags & O_EXCL)
+ lookup_flags |= LOOKUP_EXCL;
+
+ if (d_in_lookup(dentry)) {
+ struct dentry *res = nfs_lookup(dir, dentry, open_flags);
+
+ d_lookup_done(dentry);
+ if (unlikely(res)) {
+ if (IS_ERR(res))
+ return PTR_ERR(res);
+ return finish_no_open(file, res);
+ }
+ }
+
+ /* Negative dentry, just create the file */
+ if (!dentry->d_inode && (open_flags & O_CREAT)) {
+ file->f_mode |= FMODE_CREATED;
+ error = nfs_do_create(NULL, dir, dentry, mode,
+ open_flags & O_EXCL, open_flags & O_TRUNC);
+ if (error)
+ return error;
+ }
+ return finish_open(file, dentry, NULL);
+}
+EXPORT_SYMBOL_GPL(nfs_atomic_open_v23);
+
struct dentry *
nfs_add_or_obtain(struct dentry *dentry, struct nfs_fh *fhandle,
struct nfs_fattr *fattr)
@@ -2303,8 +2344,8 @@ EXPORT_SYMBOL_GPL(nfs_instantiate);
* that the operation succeeded on the server, but an error in the
* reply path made it appear to have failed.
*/
-int nfs_create(struct mnt_idmap *idmap, struct inode *dir,
- struct dentry *dentry, umode_t mode, bool excl)
+static int nfs_do_create(struct mnt_idmap *idmap, struct inode *dir,
+ struct dentry *dentry, umode_t mode, bool excl, bool trunc)
{
struct iattr attr;
int open_flags = excl ? O_CREAT | O_EXCL : O_CREAT;
@@ -2315,6 +2356,10 @@ int nfs_create(struct mnt_idmap *idmap, struct inode *dir,
attr.ia_mode = mode;
attr.ia_valid = ATTR_MODE;
+ if (trunc) {
+ attr.ia_size = 0;
+ attr.ia_valid |= ATTR_SIZE;
+ }
trace_nfs_create_enter(dir, dentry, open_flags);
error = NFS_PROTO(dir)->create(dir, dentry, &attr, open_flags);
@@ -2326,6 +2371,12 @@ int nfs_create(struct mnt_idmap *idmap, struct inode *dir,
d_drop(dentry);
return error;
}
+
+int nfs_create(struct mnt_idmap *idmap, struct inode *dir,
+ struct dentry *dentry, umode_t mode, bool excl)
+{
+ return nfs_do_create(idmap, dir, dentry, mode, excl, false);
+}
EXPORT_SYMBOL_GPL(nfs_create);
/*
diff --git a/fs/nfs/nfs3proc.c b/fs/nfs/nfs3proc.c
index 2de66e4e8280..15ddf6755ede 100644
--- a/fs/nfs/nfs3proc.c
+++ b/fs/nfs/nfs3proc.c
@@ -986,6 +986,7 @@ static int nfs3_have_delegation(struct inode *inode, fmode_t flags)
static const struct inode_operations nfs3_dir_inode_operations = {
.create = nfs_create,
+ .atomic_open = nfs_atomic_open_v23,
.lookup = nfs_lookup,
.link = nfs_link,
.unlink = nfs_unlink,
diff --git a/fs/nfs/proc.c b/fs/nfs/proc.c
index ad3a321ae997..d105e5b2659d 100644
--- a/fs/nfs/proc.c
+++ b/fs/nfs/proc.c
@@ -695,6 +695,7 @@ static int nfs_have_delegation(struct inode *inode, fmode_t flags)
static const struct inode_operations nfs_dir_inode_operations = {
.create = nfs_create,
.lookup = nfs_lookup,
+ .atomic_open = nfs_atomic_open_v23,
.link = nfs_link,
.unlink = nfs_unlink,
.symlink = nfs_symlink,
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index f5ce7b101146..cacbeb397a58 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -561,6 +561,9 @@ extern int nfs_may_open(struct inode *inode, const struct cred *cred, int openfl
extern void nfs_access_zap_cache(struct inode *inode);
extern int nfs_access_get_cached(struct inode *inode, const struct cred *cred,
u32 *mask, bool may_block);
+extern int nfs_atomic_open_v23(struct inode *dir, struct dentry *dentry,
+ struct file *file, unsigned int open_flags,
+ umode_t mode);
/*
* linux/fs/nfs/symlink.c
--
2.43.0
