Re: [Qemu-devel] [PULL 08/37] iscsi: Switch to .bdrv_co_block_status()

[Eric Blake]

On 05/08/2018 10:37 AM, Peter Maydell wrote:
> On 2 March 2018 at 18:54, Kevin Wolf <address@hidden> wrote:
> > From: Eric Blake <address@hidden>
> >
> > We are gradually moving away from sector-based interfaces, towards
> > byte-based.  Update the iscsi driver accordingly.  In this case,
> > it is handy to teach iscsi_co_block_status() to handle a NULL map
> > and file parameter, even though the block layer passes non-NULL
> > values, because we also call the function directly.  For now, there
> > are no optimizations done based on the want_zero flag.
>
> > -    *pnum = sector_lun2qemu(lbasd->num_blocks, iscsilun);
> > +    *pnum = lbasd->num_blocks * iscsilun->block_size;
>
> Hi; following this change Coverity complains (CID1390646) about
> this multiplication, which is a 32-bit multiply whose result
> is then put into a 64-bit result. Is it intended to be a
> 64-bit multiply ?

Hmm, good question.  Before this patch, the block layer definitely 
capped things below 2G so that the multiply would not overflow; but in 
rewriting it to be byte-based, it also removed that cap.  I'll send a 
patch to do a 64-bit multiply, just to be safe (even though I don't know 
for sure whether iscsi_get_lba_status_task can return more blocks than 
INT_MAX/block_size).

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org