Re: [PATCH 2/2] xfs_io: allow open file permissions to be changed

[Dave Chinner <david@fromorbit.com>]

On Mon, Dec 03, 2018 at 11:17:05AM +0100, Jan Tulak wrote:
> On Sun, Dec 2, 2018 at 9:54 PM Dave Chinner <david@fromorbit.com> wrote:
> >
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > I need to be able to open a file read-write, then change the
> > permissions on the file to read-only to check that copy_file_range
> > returns EPERM correctly in that case. This can't be done as root,
> > because root ignores file permissions, but as a normal user we can't
> > open a 0444 file for writing and so can't actually test writing to
> > a read-only file without some method of "open read-write, change
> > permissions to read-only, try to write to file through open
> > read-write file".
> >
> > So, allow adding or removing write permissions on an open file.
> >
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> 
> Should there be a man page update as well? Other commands from open.c
> have a corresponding man section, but:
> $ grep -c chmod man/man8/xfs_io.8
> 0

I forgot that, thanks. So many other things to deal with.

> And I wonder if the two permissions (0444 and 0664) are enough, or we
> might want to add other modes as well. But maybe that can be added
> when the need comes... Otherwise it looks good.

If we need more than "make read-only" or "make read-write" then we
can do something more. But for pretty much all the cases where fine
grained permissions are needed, the chmod command itself should
suffice....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com