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 20:38, Christoph Hellwig wrote:
> On Sat, May 16, 2020 at 11:54:31AM +0800, Coly Li wrote:
>> For a zoned device, e.g. host managed SMR hard drive, REQ_OP_ZONE_RESET
>> is to reset the LBA of a zone's write pointer back to the start LBA of
>> this zone. After the write point is reset, all previously stored data
>> in this zone is invalid and unaccessible anymore. Therefore, this op
>> code changes on disk data, belongs to a WRITE request op code.
>>
>> Current REQ_OP_ZONE_RESET is defined as number 6, but the convention of
>> the op code is, READ requests are even numbers, and WRITE requests are
>> odd numbers. See how op_is_write defined,
> 
> The convention is all about data transfer, and zone reset does not
> transfer any data.
> 

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.

This is why in patch "block: set bi_size to REQ_OP_ZONE_RESET bio" I set
bi_size to the REQ_OP_ZONE_RESET and REQ_OP_ZONE_RESET_ALL bios.

Coly Li