Re: [Qemu-devel] [PATCH 3/3] block: get max_transfer limit for char (scsi-generic) devices

[Eric Farman <farman@linux.vnet.ibm.com>]

On 01/17/2017 02:04 AM, Fam Zheng wrote:
> On Mon, 01/16 22:12, Eric Farman wrote:
>> Commit 6f607174 introduced a routine to get the maximum number
>> of bytes for a single I/O transfer for block devices, however
>> scsi generic devices are character devices, not block.  Add
>> a condition for this, with slightly different logic because
>> the value is already in bytes, and need not be converted from
>> blocks as happens for block devices.
>>
>> Signed-off-by: Eric Farman <farman@linux.vnet.ibm.com>
>> ---
>>  block/file-posix.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/block/file-posix.c b/block/file-posix.c
>> index 2115155..c0843c2 100644
>> --- a/block/file-posix.c
>> +++ b/block/file-posix.c
>> @@ -679,6 +679,13 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
>>              if (ret > 0 && ret <= BDRV_REQUEST_MAX_SECTORS) {
>>                  bs->bl.max_transfer = pow2floor(ret << BDRV_SECTOR_BITS);
>>              }
>> +        } else if (S_ISCHR(st.st_mode)) {
>> +            /* sg returns transfer length in bytes already */
>> +            int ret = hdev_get_max_transfer_length(bs, s->fd);
>> +            if (ret > 0 &&
>> +                (ret >> BDRV_SECTOR_BITS) <= BDRV_REQUEST_MAX_SECTORS) {
>> +                bs->bl.max_transfer = pow2floor(ret);
>> +            }
>
> Please keep the sectors/bytes quirk in hdev_get_max_transfer_length and always
> return bytes from there.

That's easy enough.  I'll allow a day or two before sending a v2, in 
case there's other considerations for the rats nest I've wandered into.

Thanks!

  - Eric