block: add max_hw_transfer to BlockLimits

For block host devices, I/O can happen through either the kernel file
descriptor I/O system calls (preadv/pwritev, io_submit, io_uring)
or the SCSI passthrough ioctl SG_IO.

In the latter case, the size of each transfer can be limited by the
HBA, while for file descriptor I/O the kernel is able to split and
merge I/O in smaller pieces as needed.  Applying the HBA limits to
file descriptor I/O results in more system calls and suboptimal
performance, so this patch splits the max_transfer limit in two:
max_transfer remains valid and is used in general, while max_hw_transfer
is limited to the maximum hardware size.  max_hw_transfer can then be
included by the scsi-generic driver in the block limits page, to ensure
that the stricter hardware limit is used.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index b6c4143dc7..665baf900e 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -179,7 +179,7 @@ static int scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s, int len)
         (r->req.cmd.buf[1] & 0x01)) {
         page = r->req.cmd.buf[2];
         if (page == 0xb0) {
-            uint32_t max_transfer = blk_get_max_transfer(s->conf.blk);
+            uint64_t max_transfer = blk_get_max_hw_transfer(s->conf.blk);
             uint32_t max_iov = blk_get_max_iov(s->conf.blk);
 
             assert(max_transfer);