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

Christoph Hellwig
2018-10-14T17:35:46Z

On Fri, Oct 12, 2018 at 05:08:32PM -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 | 20 +++++++++++++++-----
> fs/xfs/xfs_reflink.h | 2 +-
> 3 files changed, 17 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);

Is there any reason not to merge xfs_file_remap_range and
xfs_reflink_remap_range at this point?

> STATIC int
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index e1592e751cc2..66a8ddb9c058 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_len,
> 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_len = 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_len += range_len;
> }
>
> return 0;
> @@ -1391,7 +1394,7 @@ xfs_reflink_remap_prep(
> /*
> * Link a range of blocks from one file to another.
> */
> -int
> +loff_t
> xfs_reflink_remap_range(
> struct file *file_in,
> loff_t pos_in,
> @@ -1406,9 +1409,10 @@ xfs_reflink_remap_range(
> struct xfs_inode *dest = XFS_I(inode_out);
> struct xfs_mount *mp = src->i_mount;
> xfs_fileoff_t sfsbno, dfsbno;
> - xfs_filblks_t fsblen;
> + xfs_filblks_t fsblen, remappedfsb = 0;
> + loff_t remapped_bytes = 0;
> xfs_extlen_t cowextsize;
> - ssize_t ret;
> + int ret;
>
> if (!xfs_sb_version_hasreflink(&mp->m_sb))
> return -EOPNOTSUPP;
> @@ -1424,11 +1428,17 @@ xfs_reflink_remap_range(
>
> trace_xfs_reflink_remap_range(src, pos_in, len, dest, pos_out);
>
> + if (len == 0) {
> + ret = 0;
> + goto out_unlock;
> + }

Looking at the final tree this looks like dead (and bogus) code:

if (ret <= 0)
return ret;

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,
> + &remappedfsb, pos_out + len);
> + remapped_bytes = min_t(int64_t, len, XFS_FSB_TO_B(mp, remappedfsb));
> if (ret)
> goto out_unlock;

Shouldn't we just follow the calling convention of the method here:

negative return value: error
positive: number of bytes handled

Something like:

done = xfs_reflink_remap_blocks(src, sfsbno, dest, dfsbno,
fsblen, pos_out + len);
if (done < 0) {
xfs_reflink_remap_unlock(file_in, file_out);
trace_xfs_reflink_remap_range_error(dest, done, _RET_IP_);
return done;
}

>
> @@ -1451,7 +1461,7 @@ xfs_reflink_remap_range(
> xfs_reflink_remap_unlock(file_in, file_out);
> if (ret)
> trace_xfs_reflink_remap_range_error(dest, ret, _RET_IP_);

And then we can drop this conditional here.