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

Dave Chinner
2018-10-12T01:22:26Z

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?

> @@ -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?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com