Commit bcd4f3ac authored Jul 16, 2007 by Jens Axboe

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>

parent 56a68a50

fs/splice.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -1061,8 +1061,9 @@ ssize_t splice_direct_to_actor(struct file in, struct splice_desc sd,

		while (len) {
		size_t read_len;
		loff_t pos = sd->pos;

		ret = do_splice_to(in, &sd->pos, pipe, len, flags);
		ret = do_splice_to(in, &pos, pipe, len, flags);
		if (unlikely(ret <= 0))
		goto out_release;

		@@ -1080,6 +1081,7 @@ ssize_t splice_direct_to_actor(struct file in, struct splice_desc sd,

		bytes += ret;
		len -= ret;
		sd->pos = pos;

		if (ret < read_len)
		goto out_release;