On 07/24/2012 11:11 PM, Kent Overstreet wrote:
> Reusing bios is something that's been highly frowned upon in the past,
> but driver code keeps doing it anyways. If it's going to happen anyways,
> we should provide a generic method.
>
> This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
> was open coding it, by doing a bio_init() and resetting bi_destructor.
>
> Signed-off-by: Kent Overstreet <koverstreet@xxxxxxxxxx>
> ---
> fs/bio.c | 10 ++++++++++
> include/linux/bio.h | 1 +
> include/linux/blk_types.h | 6 ++++++
> 3 files changed, 17 insertions(+), 0 deletions(-)
>
> diff --git a/fs/bio.c b/fs/bio.c
> index 1c6c8b7..252e253 100644
> --- a/fs/bio.c
> +++ b/fs/bio.c
> @@ -261,6 +261,16 @@ void bio_init(struct bio *bio)
> }
> EXPORT_SYMBOL(bio_init);
>
> +void bio_reset(struct bio *bio)
> +{
> + /* Clear all flags below BIO_OWNS_VEC */
> + unsigned long flags = bio->bi_flags & (~0UL << BIO_OWNS_VEC);
> +
Hey I have not seen these FLAGS thing before. Are these new?
Anyway. Please NO!!! for one you need to put a big fat comment
over at flags definitions. And two what happens when one adds
a new flag. Is it reset or not reset?
I'd rather you define a flags mask for those that need to be
preserved, at header, plus a comment that any needed-to-be-preserved
cross init flags, must be added to the mask.
Never, ever, hide such crap so deep in the code.
Boaz
> + memset(bio, 0, BIO_RESET_BYTES);
> + bio->bi_flags = flags|(1 << BIO_UPTODATE);
> +}
> +EXPORT_SYMBOL(bio_reset);
> +
> /**
> * bio_alloc_bioset - allocate a bio for I/O
> * @gfp_mask: the GFP_ mask given to the slab allocator
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 2643589..ba60319 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -226,6 +226,7 @@ extern void __bio_clone(struct bio *, struct bio *);
> extern struct bio *bio_clone(struct bio *, gfp_t);
>
> extern void bio_init(struct bio *);
> +extern void bio_reset(struct bio *);
>
> extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
> extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 293547e..40411e2 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -59,6 +59,10 @@ struct bio {
> unsigned int bi_seg_front_size;
> unsigned int bi_seg_back_size;
>
> + /*
> + * Everything starting with bi_max_vecs will be preserved by bio_reset()
> + */
> +
> unsigned int bi_max_vecs; /* max bvl_vecs we can hold */
>
> atomic_t bi_cnt; /* pin count */
> @@ -93,6 +97,8 @@ struct bio {
> struct bio_vec bi_inline_vecs[0];
> };
>
> +#define BIO_RESET_BYTES offsetof(struct bio, bi_max_vecs)
> +
> /*
> * bio flags
> */
--
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