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Date: Mon, 03 Aug 2015 08:45:14 +0200
From: Peter Lieven <pl@kamp.de>
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Subject: Re: [Qemu-devel] Forbid to pass lun 0 to iscsi driver
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To: Andrey Korolyov <andrey@xdel.ru>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, ronniesahlberg@gmail.com

Am 02.08.2015 um 13:42 schrieb Andrey Korolyov:
> Hello,
>
> As we will never pass LUN#0 as a storage lun, it would be better to
> prohibit this at least in iscsi.c, otherwise it will result in an FPU
> exception and emulator crash:
>
> traps: qemu-system-x86[32430] trap divide error ip:7f1dab7b5073
> sp:7f1d713e4ae0 error:0 in block-iscsi.so[7f1dab7b0000+8000]
>
>      353 static bool is_request_lun_aligned(int64_t sector_num, int nb_sectors,
>      354                                       IscsiLun *iscsilun)
>      355 {
>      356     if ((sector_num * BDRV_SECTOR_SIZE) % iscsilun->block_size ||
>      357         (nb_sectors * BDRV_SECTOR_SIZE) % iscsilun->block_size) {
>
> As far as I can see the LUN#0 can be thrown out on a top level, as one
> will never use it directly as an iSCSI backend. Please correct me if
> I`m wrong in this assumption.

Hi Andrey,

LUN 0 is quite common on iSCSI targets. I think what causes the problem
is not the LUN ID, but the target which returns 0 for the blocksize. Which
target are you using?

Peter