Re: [PATCH REPOST 3/4] rbd: add a warning in bio_chain_clone_range()

[Josh Durgin <josh.durgin@inktank.com>]

On 01/03/2013 11:12 AM, Alex Elder wrote:
> Add a warning in bio_chain_clone_range() to help a user determine
> what exactly might have led to a failure.  There is only one; please
> say something if you disagree with the following reasoning.
>
> There are three places this can return abnormally:
>      - Initially, if there is nothing to clone.  It turns out that
>        right now this cannot happen anyway.  The test is in place
>        because the code below it doesn't work if those conditions
>        don't hold.  As such they could be assertions but since I can
>        return a null to indicate an error I just do that instead.
>        I have not added a warning here because it won't happen.
>      - While processing bio's, if none remain but there are supposed
>        to be more bytes to clone.  Here I have added a warning.
>      - If bio_clone_range() returns a null pointer.  That function
>        will have already produced a warning (at least the first
>        time, via WARN_ON_ONCE()) to distinguish the cause of the
>        error.  The only exception is memory exhaustion, and I'd
>        rather not pepper the code with warnings in all those spots.
>        So no warning is added in that place.
>
> Signed-off-by: Alex Elder <elder@inktank.com>
> ---

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

>   drivers/block/rbd.c |    4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 31da8c5..ce6c0cb 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -993,8 +993,10 @@ static struct bio *bio_chain_clone_range(struct bio
> **bio_src,
>   		unsigned int bi_size;
>   		struct bio *bio;
>
> -		if (!bi)
> +		if (!bi) {
> +			rbd_warn(NULL, "bio_chain exhausted with %u left", len);
>   			goto out_err;	/* EINVAL; ran out of bio's */
> +		}
>   		bi_size = min_t(unsigned int, bi->bi_size - off, len);
>   		bio = bio_clone_range(bi, off, bi_size, gfpmask);
>   		if (!bio)
>