Re: [PATCH 7/7] ext4: add support for write stream IDs

[Jens Axboe <axboe@fb.com>]

On 03/26/2015 02:34 PM, Ming Lin-SSI wrote:
>> -----Original Message-----
>> From: Jens Axboe [mailto:axboe@fb.com]
>> Sent: Wednesday, March 25, 2015 8:08 AM
>> To: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org
>> Cc: Ming Lin-SSI; david@fromorbit.com; Jens Axboe
>> Subject: [PATCH 7/7] ext4: add support for write stream IDs
>>
>> Signed-off-by: Jens Axboe <axboe@fb.com>
>> ---
>>  fs/ext4/page-io.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c index
>> b24a2541a9ba..f642d0b87a32 100644
>> --- a/fs/ext4/page-io.c
>> +++ b/fs/ext4/page-io.c
>> @@ -390,6 +390,7 @@ submit_and_retry:
>>  		ret = io_submit_init_bio(io, bh);
>>  		if (ret)
>>  			return ret;
>> +		bio_set_streamid(io->io_bio, inode_streamid(inode));
> 
> For "writeback" and "ordered" journal mode, it should be OK.
> 
> But for "journal" journal mode, 
> Step1: data written to journal
> Step2: data written from journal to fs
> 
> Do we need other code to carry stream_id in step2?

For either mode, arguably the journal should be written with its own
stream ID. But that's a subject that the filesystem guys need to tackle,
once the support is one.

For the case of maintaining stream ID when in data=journal mode and
copying the data out, I doubt that a use case that anyone would care
about. If they do, the ext4/3 guys would need to sort that out.

I'll update the commit message to reflect that, it is a bit under
explained at the moment.

-- 
Jens Axboe