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    SubjectRe: [PATCH] loop sendfile retval
    On Mon, 11 Nov 2002, Linus Torvalds wrote:
    > On Mon, 11 Nov 2002, Hugh Dickins wrote:
    > >
    > > Buffer I/O error on device loop: its use of sendfile is (trivially)
    > > broken - retval is usually count done, only an error when negative.
    > Hmm.. Sendfile can return other values than "count" (ie a partial read).
    > This return value change makes "do_lo_receive()" lose that information. As
    > such, the new do_lo_receive() is weaker than the old one.

    True, with that patch it's passing back less info than 2.5.47 tried to do;
    but no less than 2.5.46 and earlier, which always returned desc.error and
    ignored the desc.written, desc.count coming back from do_generic_file_read.
    So it's not a regression, but of course you're right that it's weak.

    > If fixing the loop code to handle partial IO is too nasty, then I would
    > suggest doing maybe something like
    > if (ret > 0 && ret != bvec->bv_len)
    > ret = -EIO;
    > which at least makes a partial IO an error instead of making it a success
    > case (the code as-is seems to think that any non-negative return value
    > means that the IO was fully successful).
    > > Nearby spinlocking clearly bogus, delete instead of remarking on it.
    > I'll apply the patch, it looks better than what is there now, but it might
    > be worth fixing this _right_.

    Thanks, that gets it going again. I'll step aside and leave the correct
    partial handling to those who know loop much better than I - Adam?


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