Re: [PATCH v3 06/13] vfs: introduce file_modified() helper

[Amir Goldstein <amir73il@gmail.com>]

On Wed, May 29, 2019 at 9:27 PM Darrick J. Wong <darrick.wong@oracle.com> wrote:
>
> On Wed, May 29, 2019 at 08:43:10PM +0300, Amir Goldstein wrote:
> > The combination of file_remove_privs() and file_update_mtime() is
> > quite common in filesystem ->write_iter() methods.
> >
> > Modelled after the helper file_accessed(), introduce file_modified()
> > and use it from generic_remap_file_range_prep().
> >
> > Note that the order of calling file_remove_privs() before
> > file_update_mtime() in the helper was matched to the more common order by
> > filesystems and not the current order in generic_remap_file_range_prep().
> >
> > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > ---
> >  fs/inode.c         | 20 ++++++++++++++++++++
> >  fs/read_write.c    | 21 +++------------------
> >  include/linux/fs.h |  2 ++
> >  3 files changed, 25 insertions(+), 18 deletions(-)
> >
> > diff --git a/fs/inode.c b/fs/inode.c
> > index df6542ec3b88..2885f2f2c7a5 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -1899,6 +1899,26 @@ int file_update_time(struct file *file)
> >  }
> >  EXPORT_SYMBOL(file_update_time);
> >
> > +/* Caller must hold the file's inode lock */
> > +int file_modified(struct file *file)
> > +{
> > +     int err;
> > +
> > +     /*
> > +      * Clear the security bits if the process is not being run by root.
> > +      * This keeps people from modifying setuid and setgid binaries.
> > +      */
> > +     err = file_remove_privs(file);
> > +     if (err)
> > +             return err;
> > +
> > +     if (likely(file->f_mode & FMODE_NOCMTIME))
>
> I would not have thought NOCMTIME is likely?
>
> Maybe it is for io requests coming from overlayfs, but for regular uses
> I don't think that's true.

Nope that's a typo. Good spotting.
Overlayfs doesn't set FMODE_NOCMTIME (yet). Only xfs does from
XFS_IOC_OPEN_BY_HANDLE, but I think Dave said that is a deprecated
API. so should have been very_unlikely().

Thanks,
Amir.