Re: [PATCH v3 01/13] fsnotify: annotate directory entry modification events

[Jan Kara <jack@suse.cz>]

On Sun 25-11-18 15:43:40, Amir Goldstein wrote:
> "dirent" events are referring to events that modify directory entries,
> such as create,delete,rename. Those events should always be reported
> on a watched directory, regardless if FS_EVENT_ON_CHILD is set
> on the watch mask.
> 
> fsnotify_nameremove() and fsnotify_move() were modified to no longer
> set the FS_EVENT_ON_CHILD event bit. This is a semantic change to
> align with the "dirent" event definition. It has no effect on any
> existing backend, because dnotify, inotify and audit always requets the
> child events and fanotify does not get the delete,rename events.
> 
> The fsnotify_dirent() helper is used instead of fsnotify_parent() to
> report a dirent event to dentry->d_parent without FS_EVENT_ON_CHILD
> and regardless if parent has the FS_EVENT_ON_CHILD bit set.
> 
> ALL_FSNOTIFY_DIRENT_EVENTS defines all the dirent event types and
> those event types have been extracted out of FS_EVENTS_POSS_ON_CHILD.
> 
> That means for a directory with an inotify watch and only dirent
> events in the mask (i.e. create,delete,move), all children dentries
> will no longer have the DCACHE_FSNOTIFY_PARENT_WATCHED flag set.
> This will allow all events that happen on children to be optimized
> away in __fsnotify_parent() without the need to dereference
> child->d_parent->d_inode->i_fsnotify_mask.
> 
> Since the dirent events are never repoted via __fsnotify_parent(),
> this results in no change of logic, but only an optimization.
> 
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  include/linux/fsnotify.h         | 43 +++++++++++++++++++++++++-------
>  include/linux/fsnotify_backend.h | 36 +++++++++++++++-----------
>  2 files changed, 55 insertions(+), 24 deletions(-)

The patch looks good. Just one question and two nits below.

> +static inline int fsnotify_dirent(struct inode *dir, struct dentry *dentry,
> +				  __u32 mask)
> +{
> +	struct dentry *parent = NULL;
> +	int ret;
> +
> +	if (!dir) {
> +		parent = dget_parent(dentry);
> +		dir = d_inode(parent);
> +	}
> +
> +	ret = fsnotify(dir, mask, d_inode(dentry), FSNOTIFY_EVENT_INODE,
> +			dentry->d_name.name, 0);
> +
> +	dput(parent);
> +	return ret;

There's one more feature fsnotify_parent() provides - it calls
take_dentry_name_snapshot() before calling into fsnotify and uses
snapshotted name. I think you need to do the same here to provide the same
protection for fsnotify_nameremove, don't you? Or maybe you don't since
generally directory i_rwsem is held when unlinking and so dentry name cannot
change but then it would be good to assert that? Who knows what some weird
fs is doing...

> +/*
> + * This is a list of all events that may get sent to a parent based on fs event

^^^ Line too long.

> +#define ALL_FSNOTIFY_EVENTS (ALL_FSNOTIFY_DIRENT_EVENTS| \
							^^^ space here

									Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR