Re: [Qemu-devel] [PATCHv2 11/11] iscsi: assert that sectors are aligned to LUN blocksize

[Peter Lieven]

Am 01.07.2013 um 16:35 schrieb Stefan Hajnoczi <address@hidden>:

> On Thu, Jun 27, 2013 at 03:11:35PM +0200, Peter Lieven wrote:
>> if the blocksize of an iSCSI LUN is bigger than the BDRV_SECTOR_SIZE
>> it is possible that sector_num or nb_sectors are not correctly
>> alligned.
>> 
>> to avoid corruption we fail requests which are misaligned.
>> 
>> Signed-off-by: Peter Lieven <address@hidden>
>> ---
>> block/iscsi.c |   27 +++++++++++++++++++++++++++
>> 1 file changed, 27 insertions(+)
>> 
>> diff --git a/block/iscsi.c b/block/iscsi.c
>> index 0567b46..bff2e1f 100644
>> --- a/block/iscsi.c
>> +++ b/block/iscsi.c
>> @@ -298,6 +298,13 @@ static int64_t sector_lun2qemu(int64_t sector, IscsiLun 
>> *iscsilun)
>>     return sector * iscsilun->block_size / BDRV_SECTOR_SIZE;
>> }
>> 
>> +static int64_t is_request_lun_aligned(int64_t sector_num, int nb_sectors,
>> +                                      IscsiLun *iscsilun)
>> +{
>> +    return ((sector_num * BDRV_SECTOR_SIZE) % iscsilun->block_size ||
>> +            (nb_sectors * BDRV_SECTOR_SIZE) % iscsilun->block_size) ? 0 : 1;
>> +}
> 
> When QEMU does geometry probing it reads 2KB.  So if the LUN has 4KB
> block size then QEMU will fail to open it?  This would also affect image
> formats on top of iSCSI LUNs.

opening a 4K LUN does not fail with my target. So writing unaligned sectors will
result in corruption. we should at least fail all those unaligned operations 
until
we have a fix or workaround in place in place.

> 
> AFAICT we have no way to passing I/O topology information up from the
> block driver.

not at the moment. Paolo had a patch series back in Dec 2011, but it never went
upstream. I asked him off list and he told me that 4K drives where not important
enough and the Redhat bug for this was closed. Now with 4K iSCSI targets these
old work could become important again.

It would be nice to find out if there was anything wrong with them or what has 
to
be done to get them integrated.

Peter