Re: [RFC PATCH v2 1/4] block: change REQ_OP_ZONE_RESET from 6 to 13

[Coly Li <colyli@suse.de>]

On 2020/5/16 23:36, Christoph Hellwig wrote:
> On Sat, May 16, 2020 at 09:05:39PM +0800, Coly Li wrote:
>> On 2020/5/16 20:50, Christoph Hellwig wrote:
>>> On Sat, May 16, 2020 at 08:44:45PM +0800, Coly Li wrote:
>>>> Yes you are right, just like REQ_OP_DISCARD which does not transfer any
>>>> data but changes the data on device. If the request changes the stored
>>>> data, it does transfer data.
>>>
>>> REQ_OP_DISCARD is a special case, because most implementation end up
>>> transferring data, it just gets attached in the low-level driver.
>>>
>>
>> Yes, REQ_OP_ZONE_RESET and REQ_OP_ZONE_RESET_ALL are quite similar to
>> REQ_OP_DISCARD. Data read from the LBA range of reset zone is not
>> suggested and the content is undefined.
>>
>> For bcache, similar to REQ_OP_DISCARD, REQ_OP_ZONE_RESET and
>> REQ_OP_ZONE_RESET_ALL are handled in same way: If the backing device
>> supports discard/zone_reset, and the operation successes, then cached
>> data on SSD covered by the LBA range should be invalid, otherwise users
>> will read outdated and garbage data.
>>
>> We should treat REQ_OP_ZONE_RESET and REQ_OP_ZONE_RESET_ALL being in
>> WRITE direction.
> 
> No, the difference is that the underlying SCSI/ATA/NVMe command tend to
> usually actually transfer data.  Take a look at the special_vec field
> in struct request and the RQF_SPECIAL_PAYLOAD flag.
> 

Then bio_data_dir() will be problematic, as it is defined,
 52 /*
 53  * Return the data direction, READ or WRITE.
 54  */
 55 #define bio_data_dir(bio) \
 56         (op_is_write(bio_op(bio)) ? WRITE : READ)

For the REQ_OP_ZONE_RESET bio, bio_data_dir() will report it as READ.

Since the author is you, how to fix this ?

Coly Li