[PATCH 2/9] block: add scatterlist-less DMA mapping helpers
Daniel Gomez
da.gomez at kernel.org
Mon Jun 16 05:37:43 PDT 2025
On 16/06/2025 13.31, Christoph Hellwig wrote:
> On Mon, Jun 16, 2025 at 08:43:22AM +0200, Daniel Gomez wrote:
>>>> This comment does not match with blk_rq_dma_map_iter_start(). It returns false
>>>> and status is BLK_STS_INVAL.
>>>
>>> I went over you comment a few times and still don't understand it.
>>
>> The way I read the comment is that status is only valid when
>> blk_rq_dma_map_iter_* returns false.
>
> Yes.
>
>> But blk_rq_dma_map_iter_start() can return false and an invalid status (in the
>> default switch case).
>
> The status field is valid. Your patch below leaves it uninitialized
> instead, which leaves me even more confused than the previous comment.
>
status is initialized at line 160 after memset():
iter->status = BLK_STS_OK;
So, what the patch does is (for blk_rq_dma_map_iter_start()):
1. Initialize status to valid (line 160)
iter->status = BLK_STS_OK;
2. In the if/switch case default case (line 181-183):
It sets the status to invalid and *iter_start() returns false:
default:
iter->status = BLK_STS_INVAL;
return false;
Removing the invalid assignment "makes it" valid (because of the initialization)
and also matches with the blk_dma_iter data struct comment (lines 13-14 in
blk-mq-dma.h):
/* Status code. Only valid when blk_rq_dma_map_iter_* returned false */
blk_status_t status;
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