linux-ext4 - Re: [PATCH v7 09/18] fanotify: introduce FAN_PRE

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Message-ID: <20241115114755.whr4q3tuj5rdj7hm@quack3>
Date: Fri, 15 Nov 2024 12:47:55 +0100
From: Jan Kara <jack@...e.cz>
To: Amir Goldstein <amir73il@...il.com>
Cc: Josef Bacik <josef@...icpanda.com>, kernel-team@...com,
	linux-fsdevel@...r.kernel.org, jack@...e.cz, brauner@...nel.org,
	torvalds@...ux-foundation.org, linux-xfs@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-mm@...ck.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v7 09/18] fanotify: introduce FAN_PRE_ACCESS permission
 event

On Fri 15-11-24 12:28:01, Amir Goldstein wrote:
> On Tue, Nov 12, 2024 at 6:56 PM Josef Bacik <josef@...icpanda.com> wrote:
> >
> > From: Amir Goldstein <amir73il@...il.com>
> >
> > Similar to FAN_ACCESS_PERM permission event, but it is only allowed with
> > class FAN_CLASS_PRE_CONTENT and only allowed on regular files and dirs.
> >
> > Unlike FAN_ACCESS_PERM, it is safe to write to the file being accessed
> > in the context of the event handler.
> >
> > This pre-content event is meant to be used by hierarchical storage
> > managers that want to fill the content of files on first read access.
> >
> > Signed-off-by: Amir Goldstein <amir73il@...il.com>
> > ---
> >  fs/notify/fanotify/fanotify.c      |  3 ++-
> >  fs/notify/fanotify/fanotify_user.c | 22 +++++++++++++++++++---
> >  include/linux/fanotify.h           | 14 ++++++++++----
> >  include/uapi/linux/fanotify.h      |  2 ++
> >  4 files changed, 33 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> > index 2e6ba94ec405..da6c3c1c7edf 100644
> > --- a/fs/notify/fanotify/fanotify.c
> > +++ b/fs/notify/fanotify/fanotify.c
> > @@ -916,8 +916,9 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
> >         BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);
> >         BUILD_BUG_ON(FAN_FS_ERROR != FS_ERROR);
> >         BUILD_BUG_ON(FAN_RENAME != FS_RENAME);
> > +       BUILD_BUG_ON(FAN_PRE_ACCESS != FS_PRE_ACCESS);
> >
> > -       BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 21);
> > +       BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 22);
> >
> >         mask = fanotify_group_event_mask(group, iter_info, &match_mask,
> >                                          mask, data, data_type, dir);
> > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> > index 9cc4a9ac1515..2ec0cc9c85cf 100644
> > --- a/fs/notify/fanotify/fanotify_user.c
> > +++ b/fs/notify/fanotify/fanotify_user.c
> > @@ -1633,11 +1633,23 @@ static int fanotify_events_supported(struct fsnotify_group *group,
> >                                      unsigned int flags)
> >  {
> >         unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
> > +       bool is_dir = d_is_dir(path->dentry);
> >         /* Strict validation of events in non-dir inode mask with v5.17+ APIs */
> >         bool strict_dir_events = FAN_GROUP_FLAG(group, FAN_REPORT_TARGET_FID) ||
> >                                  (mask & FAN_RENAME) ||
> >                                  (flags & FAN_MARK_IGNORE);
> >
> > +       /*
> > +        * Filesystems need to opt-into pre-content evnets (a.k.a HSM)
> > +        * and they are only supported on regular files and directories.
> > +        */
> > +       if (mask & FANOTIFY_PRE_CONTENT_EVENTS) {
> > +               if (!(path->mnt->mnt_sb->s_iflags & SB_I_ALLOW_HSM))
> > +                       return -EINVAL;
> 
> Should we make this return -EOPNOTSUPP?

I see no reason not to do that so go ahead.

								Honza

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