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scsi-generic: pass max_segments via max_iov field in BlockLimits 

I/O to a disk via read/write is not limited by the number of segments allowed
by the host adapter; the kernel can split requests if needed, and the limit
imposed by the host adapter can be very low (256k or so) to avoid that SG_IO
returns EINVAL if memory is heavily fragmented.

Since this value is only interesting for SG_IO-based I/O, do not include
it in the max_transfer and only take it into account when patching the
block limits VPD page in the scsi-generic device.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Paolo Bonzini 2021-04-14 19:51:48 +02:00
parent 8ad5ab6148
commit 01ef8185b8
2 changed files with 5 additions and 4 deletions
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3
block/file-posix.c
View File

@ -1237,8 +1237,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
ret = sg_get_max_segments(s->fd);
if (ret > 0) {
bs->bl.max_transfer = MIN(bs->bl.max_transfer,
ret * qemu_real_host_page_size);
bs->bl.max_iov = ret;
}
}

6
hw/scsi/scsi-generic.c
View File

@ -179,10 +179,12 @@ 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) / s->blocksize;
uint32_t max_transfer = blk_get_max_transfer(s->conf.blk);
uint32_t max_iov = blk_get_max_iov(s->conf.blk);
assert(max_transfer);
max_transfer = MIN_NON_ZERO(max_transfer, max_iov * qemu_real_host_page_size)
/ s->blocksize;
stl_be_p(&r->buf[8], max_transfer);
/* Also take care of the opt xfer len. */
stl_be_p(&r->buf[12],