Re: [PATCH v2 1/4] generic/377: Add copy to new file test

[Dave Chinner <david@fromorbit.com>]

On Fri, Sep 09, 2016 at 03:01:46PM +0800, Eryu Guan wrote:
> On Thu, Sep 08, 2016 at 11:29:25PM -0700, Darrick J. Wong wrote:
> > > > +
> > > > +_require_xfs_io_command "copy_range"
> > > 
> > > Do we need to test the support status on kernel side? e.g. what happens
> > > if filesystems have no "copy_file_range" implemented? Seems
> > > copy_file_range falls back to splice in this case, but I'm not sure. If
> > > so I think it's OK to have no kernel side detection.
> > 
> > But... it's a totally new syscall, so _require_io_command should actually try
> > calling it so that we can _notrun on old kernels.
> 
> The only reason that I think it's OK to check xfs_io support only is
> that the "copy_range" subcommand won't be even compiled in xfs_io if
> kernel has no copy_file_range syscall support.

It's not uncommon to have an xfs_io that will support a new syscall
or syscall flags by directly coding the support when it's
not found by the configure script. e.g. io/prealloc.c support for
all the different fallocate flags, regardless of whether the
underlying kernel or userspace headers support them.

> But yeah, I agree that calling it and see how kernel handles it would be
> the best option, like how we handle falloc, fpunch in
> _require_xfs_io_command.

Which we do for precisely the reason above. :P

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com