[PATCH 10/11] nvmet: translate placement identifiers of writes to write streams

[Guixin Liu]

在 2026/10/19 11:44, sashiko-bot at kernel.org 写道:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] nvmet: bi_write_stream lost on chained bios in nvmet_bdev_execute_rw()
> --
>
> commit ee4faa4396ddf960be1a3f58157a725fb3691c6f
> Author: Guixin Liu <kanie at linux.alibaba.com>
>
> nvmet: translate placement identifiers of writes to write streams
>
> This commit translates NVMe Data Placement Directive placement identifiers
> on write commands into block layer write streams on the backing block
> device when FDP is enabled on the namespace.
>
>> diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
>> index f2d9e8901df4e..ff480f9ab9906 100644
>> --- a/drivers/nvme/target/io-cmd-bdev.c
>> +++ b/drivers/nvme/target/io-cmd-bdev.c
>> @@ -300,6 +300,10 @@ static void nvmet_bdev_execute_rw(struct nvmet_req *req)
>>  	bio->bi_iter.bi_sector = sector;
>>  	bio->bi_private = req;
>>  	bio->bi_end_io = nvmet_bio_done;
>> +	if (req->cmd->rw.opcode == nvme_cmd_write &&
>> +	    nvmet_fdp_enabled(req->ns)) {
>> +		bio->bi_write_stream = nvmet_fdp_write_stream(req);
>> +	}
>>  
>>  	blk_start_plug(&plug);
>>  	if (req->metadata_len)
> [Severity: Medium]
> What happens when a write command spans multiple bios in
> nvmet_bdev_execute_rw()?
>
> When req->sg_cnt exceeds BIO_MAX_VECS (or bio_add_page() otherwise fills
> the current bio), the for_each_sg() loop allocates a new chained bio:
>
> 	for_each_sg(req->sg, sg, req->sg_cnt, i) {
> 		while (bio_add_page(bio, sg_page(sg), sg->length, sg->offset)
> 				!= sg->length) {
> 			struct bio *prev = bio;
> 			...
> 			bio = bio_alloc(req->ns->bdev, bio_max_segs(sg_cnt),
> 					opf, GFP_KERNEL);
> 			bio->bi_iter.bi_sector = sector;
>
> 			bio_chain(bio, prev);
> 			submit_bio(prev);
> 		}
>
> Since bio_alloc() initializes bi_write_stream to 0 and bio_chain() does
> not copy bi_write_stream from prev, won't all subsequent chained bios for
> the write command be submitted with bi_write_stream set to 0 instead of
> the stream returned by nvmet_fdp_write_stream(req), preventing them from
> merging with the initial bio and routing the tail of the write to the
> default stream instead of the host-selected reclaim unit?
>
> [ ... ]
Sashiko is right, fixed in v2.
>