Re: [PATCH 2/2] block: remove the bi_inline_vecs variable sized array from struct bio

[John Garry <john.g.garry@oracle.com>]

On 09/09/2025 09:40, Yu Kuai wrote:
> 
> 在 2025/09/09 16:16, John Garry 写道:
>>> diff --git a/drivers/md/bcache/movinggc.c b/drivers/md/bcache/movinggc.c
>>> index 4fc80c6d5b31..73918e55bf04 100644
>>> --- a/drivers/md/bcache/movinggc.c
>>> +++ b/drivers/md/bcache/movinggc.c
>>> @@ -145,9 +145,9 @@ static void read_moving(struct cache_set *c)
>>>               continue;
>>>           }
>>> -        io = kzalloc(struct_size(io, bio.bio.bi_inline_vecs,
>>> -                     DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS)),
>>> -                 GFP_KERNEL);
>>> +        io = kzalloc(sizeof(*io) + sizeof(struct bio_vec) *
>>> +                DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
>>> +                GFP_KERNEL);
>>
>> this seems a common pattern, so maybe another helper (which could be 
>> used by bio_kmalloc)? I am not advocating it, but just putting the 
>> idea out there... too many helpers makes it messy IMHO
> 
> Not sure how to do this, do you mean a marco to pass in the base
> structure type, nr_vecs and the gfp_mask?

something like the following (which I think is messy and an imprecise 
API, so again I am not advocating it):

struct bio *bio_kmalloc(unsigned short nr_vecs, gfp_t gfp_mask)
{
	return kmalloc(sizeof(struct bio) + nr_vecs * sizeof(struct bio_vec),
gfp_mask);
}

struct bio *bio_kmalloc_inline(unsigned short nr_vecs, gfp_t gfp_mask)
{
	if (nr_vecs > BIO_MAX_INLINE_VECS)
		return NULL;
	return bio_kmalloc(nr_vecs, gfp_mask);
}