On Wed, Jun 12, 2024 at 10:10 AM NeilBrown <neilb@xxxxxxx> wrote:
>
>
> When a file is opened and created with open(..., O_CREAT) we get
> both the CREATE and OPEN fsnotify events and would expect them in that
> order. For most filesystems we get them in that order because
> open_last_lookups() calls fsnofify_create() and then do_open() (from
> path_openat()) calls vfs_open()->do_dentry_open() which calls
> fsnotify_open().
>
> However when ->atomic_open is used, the
> do_dentry_open() -> fsnotify_open()
> call happens from finish_open() which is called from the ->atomic_open
> handler in lookup_open() which is called *before* open_last_lookups()
> calls fsnotify_create. So we get the "open" notification before
> "create" - which is backwards. ltp testcase inotify02 tests this and
> reports the inconsistency.
>
> This patch lifts the fsnotify_open() call out of do_dentry_open() and
> places it higher up the call stack. There are three callers of
> do_dentry_open().
>
> For vfs_open() and kernel_file_open() the fsnotify_open() is placed
> directly in that caller so there should be no behavioural change.
>
> For finish_open() there are two cases:
> - finish_open is used in ->atomic_open handlers. For these we add a
> call to fsnotify_open() at the top of do_open() if FMODE_OPENED is
> set - which means do_dentry_open() has been called.
> - finish_open is used in ->tmpfile() handlers. For these a similar
> call to fsnotify_open() is added to vfs_tmpfile()
Any handlers other than ovl_tmpfile()?
This one is a very recent and pretty special case.
Did open(O_TMPFILE) used to emit an OPEN event before that change?
>
> With this patch NFSv3 is restored to its previous behaviour (before
> ->atomic_open support was added) of generating CREATE notifications
> before OPEN, and NFSv4 now has that same correct ordering that is has
> not had before. I haven't tested other filesystems.
>
> Fixes: 7c6c5249f061 ("NFS: add atomic_open for NFSv3 to handle O_TRUNC correctly.")
> Reported-by: James Clark <james.clark@xxxxxxx>
> Closes: https://lore.kernel.org/all/01c3bf2e-eb1f-4b7f-a54f-d2a05dd3d8c8@xxxxxxx
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> fs/namei.c | 5 +++++
> fs/open.c | 19 ++++++++++++-------
> 2 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 37fb0a8aa09a..057afacc4b60 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3612,6 +3612,9 @@ static int do_open(struct nameidata *nd,
> int acc_mode;
> int error;
>
> + if (file->f_mode & FMODE_OPENED)
> + fsnotify_open(file);
> +
> if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) {
> error = complete_walk(nd);
> if (error)
> @@ -3700,6 +3703,8 @@ int vfs_tmpfile(struct mnt_idmap *idmap,
> mode = vfs_prepare_mode(idmap, dir, mode, mode, mode);
> error = dir->i_op->tmpfile(idmap, dir, file, mode);
> dput(child);
> + if (file->f_mode & FMODE_OPENED)
> + fsnotify_open(file);
> if (error)
> return error;
> /* Don't check for other permissions, the inode was just created */
> diff --git a/fs/open.c b/fs/open.c
> index 89cafb572061..970f299c0e77 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -1004,11 +1004,6 @@ static int do_dentry_open(struct file *f,
> }
> }
>
> - /*
> - * Once we return a file with FMODE_OPENED, __fput() will call
> - * fsnotify_close(), so we need fsnotify_open() here for symmetry.
> - */
> - fsnotify_open(f);
> return 0;
>
> cleanup_all:
> @@ -1085,8 +1080,17 @@ EXPORT_SYMBOL(file_path);
> */
> int vfs_open(const struct path *path, struct file *file)
> {
> + int ret;
> +
> file->f_path = *path;
> - return do_dentry_open(file, NULL);
> + ret = do_dentry_open(file, NULL);
> + if (!ret)
> + /*
> + * Once we return a file with FMODE_OPENED, __fput() will call
> + * fsnotify_close(), so we need fsnotify_open() here for symmetry.
> + */
> + fsnotify_open(file);
I agree that this change preserves the logic, but (my own) comment
above is inconsistent with the case of:
if ((f->f_flags & O_DIRECT) && !(f->f_mode & FMODE_CAN_ODIRECT))
return -EINVAL;
Which does set FMODE_OPENED, but does not emit an OPEN event.
I have a feeling that the comment is correct about the CLOSE event in
that case, but honestly, I don't think this corner case is that important,
just maybe the comment needs to be slightly clarified?
Thanks,
Amir.
> + return ret;
> }
>
> struct file *dentry_open(const struct path *path, int flags,
> @@ -1178,7 +1182,8 @@ struct file *kernel_file_open(const struct path *path, int flags,
> if (error) {
> fput(f);
> f = ERR_PTR(error);
> - }
> + } else
> + fsnotify_open(f);
> return f;
> }
> EXPORT_SYMBOL_GPL(kernel_file_open);
> --
> 2.44.0
>
