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    SubjectRe: [PATCH v4 03/12] block: Add bio_reset()
    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@google.com>
    > ---
    > 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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