Re: [Qemu-stable] [PULL 3/6] iscsi: Fix divide-by-zero regression on raw SG devices

[Eric Blake]

On 09/22/2016 11:52 AM, Paolo Bonzini wrote:
> From: Eric Blake <address@hidden>
> 
> When qemu uses iscsi devices in sg mode, iscsilun->block_size
> is left at 0.  Prior to commits cf081fca and similar, when
> block limits were tracked in sectors, this did not matter:
> various block limits were just left at 0.  But when we started
> scaling by block size, this caused SIGFPE.
> 

> +++ b/block/iscsi.c
> @@ -1813,19 +1813,23 @@ static void iscsi_refresh_limits(BlockDriverState 
> *bs, Error **errp)
>  
>      IscsiLun *iscsilun = bs->opaque;
>      uint64_t max_xfer_len = iscsilun->use_16_for_rw ? 0xffffffff : 0xffff;
> +    unsigned int block_size = MIN_NON_ZERO(BDRV_SECTOR_SIZE,
> +                                           iscsilun->block_size);
>  
> -    bs->bl.request_alignment = iscsilun->block_size;
> +    assert(iscsilun->block_size >= BDRV_SECTOR_SIZE || bs->sg);
> +
> +    bs->bl.request_alignment = block_size;

Ouch. If iscsilun->block_size is 4k, this ends up changing
bs->bl.request_alignment to 512, which is wrong. :(

If I'm in time, let's drop this from the pull request, and I'll send a
followup patch.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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