Re: [Qemu-devel] [PATCHv5 3/6] block/iscsi: set max_transfer_length

[Peter Lieven <pl@kamp.de>]

On 27.10.2014 09:44, Max Reitz wrote:
> On 2014-10-27 at 09:36, Peter Lieven wrote:
>> On 27.10.2014 09:28, Max Reitz wrote:
>>> On 2014-10-25 at 18:18, Peter Lieven wrote:
>>>> Copy the max_xfer_len from the BlockLimits VPD or use the
>>>> maximum value fitting in the CDB.
>>>>
>>>> Signed-off-by: Peter Lieven <pl@kamp.de>
>>>> ---
>>>>   block/iscsi.c |   17 +++++++++++++++--
>>>>   1 file changed, 15 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/block/iscsi.c b/block/iscsi.c
>>>> index 233f462..1ae4add 100644
>>>> --- a/block/iscsi.c
>>>> +++ b/block/iscsi.c
>>>> @@ -297,6 +297,11 @@ static int64_t sector_lun2qemu(int64_t sector, IscsiLun *iscsilun)
>>>>       return sector * iscsilun->block_size / BDRV_SECTOR_SIZE;
>>>>   }
>>>>   +static int nb_sectors_lun2qemu(int64_t sector, IscsiLun *iscsilun)
>>>> +{
>>>> +    return MIN(sector_lun2qemu(sector, iscsilun), INT_MAX);
>>>> +}
>>>> +
>>>>   static int64_t sector_qemu2lun(int64_t sector, IscsiLun *iscsilun)
>>>>   {
>>>>       return sector * BDRV_SECTOR_SIZE / iscsilun->block_size;
>>>> @@ -1449,10 +1454,18 @@ static void iscsi_close(BlockDriverState *bs)
>>>>     static void iscsi_refresh_limits(BlockDriverState *bs, Error **errp)
>>>>   {
>>>> -    IscsiLun *iscsilun = bs->opaque;
>>>> -
>>>>       /* We don't actually refresh here, but just return data queried in
>>>>        * iscsi_open(): iscsi targets don't change their limits. */
>>>> +
>>>> +    IscsiLun *iscsilun = bs->opaque;
>>>> +    uint32_t max_xfer_len = iscsilun->use_16_for_rw ? 0xffffffff : 0xffff;
>>>> +
>>>> +    if (iscsilun->bl.max_xfer_len) {
>>>> +        max_xfer_len = MIN(max_xfer_len, iscsilun->bl.max_xfer_len);
>>>> +    }
>>>> +
>>>> +    bs->bl.max_transfer_length = nb_sectors_lun2qemu(max_xfer_len, iscsilun);
>>>> +
>>>>       if (iscsilun->lbp.lbpu) {
>>>>           if (iscsilun->bl.max_unmap < 0xffffffff) {
>>>>               bs->bl.max_discard = sector_lun2qemu(iscsilun->bl.max_unmap,
>>>
>>> Hm, seems strange to have a function called nb_sectors_lun2qemu() not only convert values, but also cap the result. But anyway:
>>
>> Would you give it another name?
>
> Aaah, looking for names... It's always the same horror...
>
> Hm, I just realized why it's nb_sectors, it just wasn't obvious to me that nb_sectors is always an int (and I think it might not be to others either).
>
> So maybe int_sector_lun2qemu() or even better sector_lun2qemu_int()? I always consider everything on the left of the "2" to be the original unit and everything on the right to be the result unit, maybe that confused me further (so 
> sector_lun2qemu_nb_sectors() is what I'd expect, although it's rather long).
>
> But I now see why you called the function that way and it seems fine to me. Just leaving it is fine, too. ;-)

what about limits_lun2qemu ? It might give a hint that nobody uses it for sth else than limits?

Peter