Re: [PATCH 24/25] xfs: support returning partial reflink results

Darrick J. Wong
2018-10-12T16:06:30Z

On Fri, Oct 12, 2018 at 12:22:26PM +1100, Dave Chinner wrote:
> On Wed, Oct 10, 2018 at 09:15:19PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> >
> > Back when the XFS reflink code only supported clone_file_range, we were
> > only able to return zero or negative error codes to userspace. However,
> > now that copy_file_range (which returns bytes copied) can use XFS'
> > clone_file_range, we have the opportunity to return partial results.
> > For example, if userspace sends a 1GB clone request and we run out of
> > space halfway through, we at least can tell userspace that we completed
> > 512M of that request like a regular write.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > fs/xfs/xfs_file.c | 5 +----
> > fs/xfs/xfs_reflink.c | 19 ++++++++++++++-----
> > fs/xfs/xfs_reflink.h | 2 +-
> > 3 files changed, 16 insertions(+), 10 deletions(-)
> >
> >
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index bc9e94bcb7a3..b2b15b8dc4a1 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -928,14 +928,11 @@ xfs_file_remap_range(
> > loff_t len,
> > unsigned int remap_flags)
> > {
> > - int ret;
> > -
> > if (!remap_check_flags(remap_flags, RFR_SAME_DATA))
> > return -EINVAL;
> >
> > - ret = xfs_reflink_remap_range(file_in, pos_in, file_out, pos_out,
> > + return xfs_reflink_remap_range(file_in, pos_in, file_out, pos_out,
> > len, remap_flags);
> > - return ret < 0 ? ret : len;
> > }
> >
> > STATIC int
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > index e1592e751cc2..12a1fe92454e 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -1123,6 +1123,7 @@ xfs_reflink_remap_blocks(
> > struct xfs_inode *dest,
> > xfs_fileoff_t destoff,
> > xfs_filblks_t len,
> > + xfs_filblks_t *remapped,
> > xfs_off_t new_isize)
> > {
> > struct xfs_bmbt_irec imap;
> > @@ -1130,6 +1131,7 @@ xfs_reflink_remap_blocks(
> > int error = 0;
> > xfs_filblks_t range_len;
> >
> > + *remapped = 0;
> > /* drange = (destoff, destoff + len); srange = (srcoff, srcoff + len) */
> > while (len) {
> > uint lock_mode;
> > @@ -1168,6 +1170,7 @@ xfs_reflink_remap_blocks(
> > srcoff += range_len;
> > destoff += range_len;
> > len -= range_len;
> > + *remapped += range_len;
> > }
>
> So "remapped" is a block count? Can we call this something like
> remap_len so it's obvious what it is tracking?

Ok.

> > @@ -1424,11 +1427,17 @@ xfs_reflink_remap_range(
> >
> > trace_xfs_reflink_remap_range(src, pos_in, len, dest, pos_out);
> >
> > + if (len == 0) {
> > + ret = 0;
> > + goto out_unlock;
> > + }
> > +
> > dfsbno = XFS_B_TO_FSBT(mp, pos_out);
> > sfsbno = XFS_B_TO_FSBT(mp, pos_in);
> > fsblen = XFS_B_TO_FSB(mp, len);
> > ret = xfs_reflink_remap_blocks(src, sfsbno, dest, dfsbno, fsblen,
> > - pos_out + len);
> > + &remapped, pos_out + len);
> > + remapped = min_t(int64_t, len, XFS_FSB_TO_B(mp, remapped));
>
> So remapped is returned as a block count, then immediately converted
> to a byte count? Can we return it as byte count so that we don't
> have this weird unit conversion?

But then we'd have a function whose inputs are in units of blocks but
whose return value is in units of bytes.

Maybe I'll just do this to make it more explicit:

xfs_filblks_t remapped_blocks = 0;
loff_t remapped_bytes = 0;

ret = xfs_reflink_remap_blocks(..., &remapped_blocks...);
remapped_bytes = min_t(int64_t, len, XFS_FSB_TO_B(mp, remapped_blocks));

...

return remapped_bytes > 0 ? remapped_bytes : ret;

--D

> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com