Re: [PATCH 17/25] vfs: enable remap callers that can handle short operations

Amir Goldstein
2018-10-11T05:15:42Z

On Thu, Oct 11, 2018 at 7:14 AM Darrick J. Wong <darrick.wong@oracle.com> wrote:
>
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> Plumb in a remap flag that enables the filesystem remap handler to
> shorten remapping requests for callers that can handle it. Now
> copy_file_range can report partial success (in case we run up against
> alignment problems, resource limits, etc.).
>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> ---
> fs/read_write.c | 15 +++++++++------
> include/linux/fs.h | 7 +++++--
> mm/filemap.c | 16 ++++++++++++----
> 3 files changed, 26 insertions(+), 12 deletions(-)
>
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 6ec908f9a69b..3713893b7e38 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1593,7 +1593,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>
> cloned = file_in->f_op->remap_file_range(file_in, pos_in,
> file_out, pos_out,
> - min_t(loff_t, MAX_RW_COUNT, len), 0);
> + min_t(loff_t, MAX_RW_COUNT, len),
> + RFR_CAN_SHORTEN);
> if (cloned > 0) {
> ret = cloned;
> goto done;
> @@ -1804,16 +1805,18 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> * If the user is attempting to remap a partial EOF block and
> * it's inside the destination EOF then reject it.
> *
> - * We don't support shortening requests, so we can only reject
> - * them.
> + * If possible, shorten the request instead of rejecting it.
> */
> if (is_dedupe)
> ret = -EBADE;
> else if (pos_out + *len < i_size_read(inode_out))
> ret = -EINVAL;
>
> - if (ret)
> - return ret;
> + if (ret) {
> + if (!(remap_flags & RFR_CAN_SHORTEN))
> + return ret;
> + *len &= ~blkmask;
> + }
> }
>
> return 1;
> @@ -2112,7 +2115,7 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
>
> deduped = vfs_dedupe_file_range_one(file, off, dst_file,
> info->dest_offset, len,
> - 0);
> + RFR_CAN_SHORTEN);

You did not update WARN_ON_ONCE in vfs_dedupe_file_range_one()
to allow this flag and did not mention dedupe in commit message.
Was that change intentional in this patch?

After RFR_SHORT_DEDUPE patch the end result in fine.

Thanks,
Amir.