tree 03134513c5f47540814ee2d86cbb31523f722efa
parent 56a68a500fcab9e3a9a49ca7fbef14230ab7d144
author Jens Axboe <jens.axboe@oracle.com> 1184589709 +0200
committer Jens Axboe <jens.axboe@oracle.com> 1184590968 +0200

splice: direct splicing updates ppos twice

OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> reported that he's noticed
nfsd read corruption in recent kernels, and did the hard work of
discovering that it's due to splice updating the file position twice.
This means that the next operation would start further ahead than it
should.

nfsd_vfs_read()
    splice_direct_to_actor()
        while(len) {
            do_splice_to()                     [update sd->pos]
                -> generic_file_splice_read()  [read from sd->pos]
            nfsd_direct_splice_actor()
                -> __splice_from_pipe()        [update sd->pos]

There's nothing wrong with the core splice code, but the direct
splicing is an addon that calls both input and output paths.
So it has to take care in locally caching offset so it remains correct.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>