Re: [Qemu-devel] [PATCH v2 07/17] block: Give nonzero result to blk_get_max_transfer_length()
On 16/06/2016 07:25, Fam Zheng wrote:
>> > +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);
> Paolo: should we take s->blocksize into account? I missed it when I wrote this
> piece of code.
Hmm, the maximum and optimal transfer length is in logical blocks, so yes.
There is one thing that isn't great: at least Linux reads the capacity
before the block limits page, but we cannot know for sure that everyone
does it. I think it's a good idea to send a READ CAPACITY(10) at
startup, like we do in get_stream_blocksize. We only need it for the
blocksize, not for the capacity, so it's not necessary to use READ
CAPACITY(16).
The snooping is still necessary for the max_lba (which is used by
scsi_disk_dma_command), so we might as well keep the assignment to
s->blocksize in there too. But let's add a best effort READ
CAPACITY(10) at startup.
Paolo
Re: [Qemu-devel] [PATCH v2 07/17] block: Give nonzero result to blk_get_max_transfer_length()
On Tue, 06/14 15:30, Eric Blake wrote:
> 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: Eric Blake
>
> ---
> v2: new patch
> ---
> block/block-backend.c | 7 ---
> hw/block/virtio-blk.c | 3 +--
> hw/scsi/scsi-generic.c | 12 ++--
> 3 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 34500e6..1fb070b 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -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)
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 284e646..1d2792e 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -382,7 +382,7 @@ 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) {
> @@ -392,7 +392,6 @@ 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);
> diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
> index 71372a8..db04a76 100644
> --- a/hw/scsi/scsi-generic.c
> +++ b/hw/scsi/scsi-generic.c
> @@ -226,12 +226,12 @@ static void scsi_read_complete(void * opaque, int ret)
> r->req.cmd.buf[0] == INQUIRY &&
> r->req.cmd.buf[2] == 0xb0) {
> uint32_t max_xfer_len = blk_get_max_transfer_length(s->conf.blk);
> -if (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);
> -}
> +
> +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);
Paolo: should we take s->blocksize into account? I missed it when I wrote this
piece of code.
Fam
> }
> }
> scsi_req_data(&r->req, len);
> --
> 2.5.5
>
>
[Qemu-devel] [PATCH v2 07/17] 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: Eric Blake
---
v2: new patch
---
block/block-backend.c | 7 ---
hw/block/virtio-blk.c | 3 +--
hw/scsi/scsi-generic.c | 12 ++--
3 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/block/block-backend.c b/block/block-backend.c
index 34500e6..1fb070b 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -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)
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 284e646..1d2792e 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -382,7 +382,7 @@ 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) {
@@ -392,7 +392,6 @@ 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);
diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 71372a8..db04a76 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -226,12 +226,12 @@ static void scsi_read_complete(void * opaque, int ret)
r->req.cmd.buf[0] == INQUIRY &&
r->req.cmd.buf[2] == 0xb0) {
uint32_t max_xfer_len = blk_get_max_transfer_length(s->conf.blk);
-if (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);
-}
+
+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);
--
2.5.5
