On Tue, Apr 23, 2019 at 2:44 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > On Tue, Apr 23, 2019 at 2:40 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > > > On Tue, Apr 23, 2019 at 1:00 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > > > On Tue, Apr 23, 2019 at 9:51 AM Murphy Zhou <jencce.kernel@xxxxxxxxx> wrote: > > > > > > > > Overlays ovl_iter_write calls vfs_iter_write to write on real file, > > > > in which calls fsnotify_modify on this change, however vfs_write also > > > > calls fsnotify_modify after ovl_iter_write. The first notification > > > > sent by vfs_iter_write grabs marks from upper inode and overlay mnt, > > > > because of its fake path. The second one sent by vfs_write grabs marks > > > > from ovl inode and ovl mnt. > > > > > > > > LTP fanotify06 add modify mark for mnt point, then add ignore modify > > > > mask on testfile, then truncate and write the file. Because the ignore > > > > mask is marked on ovl inode, not the upper inode, the first event is not > > > > masked like the second one. So we get a modification event even with a > > > > mask on the file. > > > > > > Care to extend fanotify06 in a similar manner to the way readahead02 > > > was extended to test overlay test case regardless of the base LTP filesystem? > > > > > > > > > > > Proposing fixing this by add a new RWF flag to skip fsnotify on this IO. > > > > vfs_iter_write used by ovl can use this flag to skip one duplicate event. > > > > > > > > > > This fix is wrong for several reasons: > > > - It exports RWF_NONOTIFY to uapi > > > - It will cause no events at all when overlay writes to file even when user > > > requested events on upper inode > > > > > > Please try attached patch. > > > > Would be nice, but until mmap stops using realfile this isn't a good solution. > > > > Sigh! I figured there was a catch... > Will it be ok if fake path used a cloned private mount of overlay mount? So the reason we have the fake path is e.g. /proc/$$/maps. That can only work with the original mount, AFAICS. We could have one realfile for regular I/O and a separate one for mmap but that would increase complexity as well as resource use, so I'm not quite sure if that's the right solution. Thanks, Miklos
