On Wed, Nov 20, 2024 at 04:53:09PM +0100, Jan Kara wrote: > On Fri 15-11-24 10:30:15, Josef Bacik wrote: > > From: Amir Goldstein <amir73il@xxxxxxxxx> > > > > Legacy inotify/fanotify listeners can add watches for events on inode, > > parent or mount and expect to get events (e.g. FS_MODIFY) on files that > > were already open at the time of setting up the watches. > > > > fanotify permission events are typically used by Anti-malware sofware, > > that is watching the entire mount and it is not common to have more that > > one Anti-malware engine installed on a system. > > > > To reduce the overhead of the fsnotify_file_perm() hooks on every file > > access, relax the semantics of the legacy FAN_ACCESS_PERM event to generate > > events only if there were *any* permission event listeners on the > > filesystem at the time that the file was opened. > > > > The new semantic is implemented by extending the FMODE_NONOTIFY bit into > > two FMODE_NONOTIFY_* bits, that are used to store a mode for which of the > > events types to report. > > > > This is going to apply to the new fanotify pre-content events in order > > to reduce the cost of the new pre-content event vfs hooks. > > > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wj8L=mtcRTi=NECHMGfZQgXOp_uix1YVh04fEmrKaMnXA@xxxxxxxxxxxxxx/ > > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> > > FWIW I've ended up somewhat massaging this patch (see below). > > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > index 23bd058576b1..8e5c783013d2 100644 > > --- a/include/linux/fs.h > > +++ b/include/linux/fs.h > > @@ -173,13 +173,14 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, > > > > #define FMODE_NOREUSE ((__force fmode_t)(1 << 23)) > > > > -/* FMODE_* bit 24 */ > > - > > /* File is embedded in backing_file object */ > > -#define FMODE_BACKING ((__force fmode_t)(1 << 25)) > > +#define FMODE_BACKING ((__force fmode_t)(1 << 24)) > > > > -/* File was opened by fanotify and shouldn't generate fanotify events */ > > -#define FMODE_NONOTIFY ((__force fmode_t)(1 << 26)) > > +/* File shouldn't generate fanotify pre-content events */ > > +#define FMODE_NONOTIFY_HSM ((__force fmode_t)(1 << 25)) > > + > > +/* File shouldn't generate fanotify permission events */ > > +#define FMODE_NONOTIFY_PERM ((__force fmode_t)(1 << 26)) > > Firstly, I've kept FMODE_NONOTIFY to stay a single bit instead of two bit > constant. I've seen too many bugs caused by people expecting the constant > has a single bit set when it actually had more in my life. So I've ended up > with: > > +/* > + * Together with FMODE_NONOTIFY_PERM defines which fsnotify events shouldn't be > + * generated (see below) > + */ > +#define FMODE_NONOTIFY ((__force fmode_t)(1 << 25)) > + > +/* > + * Together with FMODE_NONOTIFY defines which fsnotify events shouldn't be > + * generated (see below) > + */ > +#define FMODE_NONOTIFY_PERM ((__force fmode_t)(1 << 26)) > > and > > +/* > + * The two FMODE_NONOTIFY* define which fsnotify events should not be generated > + * for a file. These are the possible values of (f->f_mode & > + * FMODE_FSNOTIFY_MASK) and their meaning: > + * > + * FMODE_NONOTIFY - suppress all (incl. non-permission) events. > + * FMODE_NONOTIFY_PERM - suppress permission (incl. pre-content) events. > + * FMODE_NONOTIFY | FMODE_NONOTIFY_PERM - suppress only pre-content events. > + */ > +#define FMODE_FSNOTIFY_MASK \ > + (FMODE_NONOTIFY | FMODE_NONOTIFY_PERM) This is fine by me. But I want to preemptively caution to please not spread the disease of further defines based on such multi-bit defines like fanotify does. I'm specifically worried about stuff like: #define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM | \ FS_OPEN_EXEC_PERM) #define FS_EVENTS_POSS_ON_CHILD (ALL_FSNOTIFY_PERM_EVENTS | \ FS_ACCESS | FS_MODIFY | FS_ATTRIB | \ FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | \ FS_OPEN | FS_OPEN_EXEC)
