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Re: [Qemu-block] [Qemu-devel] hostdev / iSCSI issue in QEMU 2.7


From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] hostdev / iSCSI issue in QEMU 2.7
Date: Tue, 6 Sep 2016 10:52:33 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

On 09/05/2016 04:16 AM, Kevin Wolf wrote:
> Am 01.09.2016 um 22:21 hat Holger Schranz geschrieben:
>> Hello,
>>
>> we need help for an issue we have sice QEMU 2.7.
>> May be we use the wrong mailing list. If so please let me know which
>> mail list we have to use to report problems in QEMU.
>>
>> Best regards
>>
>> Holger
> 
> Eric, a quick look suggests that this might be related to your recent
> changes to the iscsi driver. Can you have a look?

Indeed, it looks like we'll have to write a patch, and downstreams will
have to backport it until 2.7.1 stable includes it automatically.

> 
> Maybe what we really need to do is avoid calling bdrv_refresh_limits()
> for devices with bs->sg == true.

Seems like a good idea; I'll give that idea a try and post a patch
shortly, although getting Holger's help in testing it would be appreciated.
>> Thread 1 "qemu-system-x86" received signal SIGFPE, Arithmetic exception.
>> 0x0000555555c207e2 in iscsi_refresh_limits (bs=0x5555568236f0,
>>     errp=0x7fffffffcca8) at
>> /home/kvm/SOURCES/qemu-2.7.0-rc4/block/iscsi.c:1838
>> 1838        if (iscsilun->bl.max_ws_len < 0xffffffff /
>> iscsilun->block_size) {
>>
>> The function iscsi_refresh_limits is changed in 2.7RC4 and devides by
>> iscsilun->block_size,
>> but the block size is filled only for SCSI-type TYPE_DISK and TYPE_ROM in
>> /home/kvm/SOURCES/qemu-2.7.0-rc4/block/iscsi.c:1378 (function
>> iscsi_readcapacity_sync)
>>
>> If the libvirt-construction (see above) is correct, there is no chance
>> in qemu 2.7
>> to use a tape-device or changer via iscsi.
>>
>> !!! If we should change the definition, please let us know. !!!

The libvirt usage seems correct, rather, this is an unfortunate qemu
regression, and sadly was not reported in time for us to fix it for last
week's 2.7 release.

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

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