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

[John Garry]

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.