Re: [PATCH RFC 4/4] md/raid0: Atomic write support

John Garry
2024-09-12T15:39:06Z

On 12/09/2024 16:10, Christoph Hellwig wrote:
> On Thu, Sep 12, 2024 at 03:48:09PM +0100, John Garry wrote:
>>
>> I actually now think that I should change bio_split() to return NULL for
>> splitting a REQ_ATOMIC, like what do for ZONE_APPEND - calling bio_split()
>> like this is a common pattern in md RAID personalities. However, none of
>> the md RAID code check for a NULL split, which they really should, so I can
>> make that change also.
>
> bio_split is a bit of a mess - even NULL isn't very good at returning
> what caused it to fail. Maybe a switch to ERR_PTR and an audit of
> all callers might be a good idea.
>

So for bio_split() I guess that we would change as follows:

--->8----

diff --git a/block/bio.c b/block/bio.c
index c4053d49679a..36ddf458753f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1671,11 +1671,11 @@ struct bio *bio_split(struct bio *bio, int sectors,

/* Zone append commands cannot be split */
if (WARN_ON_ONCE(bio_op(bio) == REQ_OP_ZONE_APPEND))
- return NULL;
+ return ERR_PTR(-EOPNOTSUPP);

split = bio_alloc_clone(bio->bi_bdev, bio, gfp, bs);
if (!split)
- return NULL;
+ return ERR_PTR(-ENOMEM);

split->bi_iter.bi_size = sectors << 9;

---8<----

And then fix up the callers to use IS_ERR().

Or also change bio_alloc_clone() to return an ERR_PTR()? I don't see
much point in that, as we will only ever return ENOMEM (from the
callees) anyway.