Commit 24ce9a20 authored by Eric Blake's avatar Eric Blake Committed by Kevin Wolf
Browse files

block: Give nonzero result to blk_get_max_transfer_length() 



Making all callers special-case 0 as unlimited is awkward,
and we DO have a hard maximum of BDRV_REQUEST_MAX_SECTORS given
our current block layer API limits.

In the case of scsi, this means that we now always advertise a
limit to the guest, even in cases where the underlying layers
previously use 0 for no inherent limit beyond the block layer.

Signed-off-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarFam Zheng <famz@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent efaf4781

block/block-backend.c

+4 −3
Original line number Diff line number Diff line
@@ -1303,15 +1303,16 @@ int blk_get_flags(BlockBackend *blk) 
    }

}



/* Returns the maximum transfer length, in sectors; guaranteed nonzero */

int blk_get_max_transfer_length(BlockBackend *blk)

{

    BlockDriverState *bs = blk_bs(blk);

    int max = 0;



    if (bs) {

        return bs->bl.max_transfer_length;

    } else {

        return 0;

        max = bs->bl.max_transfer_length;

    }

    return MIN_NON_ZERO(max, BDRV_REQUEST_MAX_SECTORS);

}



int blk_get_max_iov(BlockBackend *blk)

hw/block/virtio-blk.c

+1 −2
Original line number Diff line number Diff line
@@ -384,7 +384,7 @@ static int multireq_compare(const void *a, const void *b) 
void virtio_blk_submit_multireq(BlockBackend *blk, MultiReqBuffer *mrb)

{

    int i = 0, start = 0, num_reqs = 0, niov = 0, nb_sectors = 0;

    int max_xfer_len = 0;

    int max_xfer_len;

    int64_t sector_num = 0;



    if (mrb->num_reqs == 1) {
@@ -394,7 +394,6 @@ void virtio_blk_submit_multireq(BlockBackend *blk, MultiReqBuffer *mrb) 
    }



    max_xfer_len = blk_get_max_transfer_length(mrb->reqs[0]->dev->blk);

    max_xfer_len = MIN_NON_ZERO(max_xfer_len, BDRV_REQUEST_MAX_SECTORS);



    qsort(mrb->reqs, mrb->num_reqs, sizeof(*mrb->reqs),

          &multireq_compare);

hw/scsi/scsi-generic.c

+6 −6
Original line number Diff line number Diff line
@@ -227,14 +227,14 @@ static void scsi_read_complete(void * opaque, int ret) 
        r->req.cmd.buf[2] == 0xb0) {

        uint32_t max_xfer_len = blk_get_max_transfer_length(s->conf.blk) /

            (s->blocksize / BDRV_SECTOR_SIZE);

        if (max_xfer_len) {



        assert(max_xfer_len);

        stl_be_p(&r->buf[8], max_xfer_len);

        /* Also take care of the opt xfer len. */

        if (ldl_be_p(&r->buf[12]) > max_xfer_len) {

            stl_be_p(&r->buf[12], max_xfer_len);

        }

    }

    }

    scsi_req_data(&r->req, len);

    scsi_req_unref(&r->req);

}