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Subject[PATCH 025 of 35] Treat rq->hard_nr_sectors as setting an overriding limit in the size of the request

For a request to be able to refer to part of a bio, we need to be able
to impose a size limit at the request level. So allow hard_nr_sectors
to be less than the size of the bios (and bio_vecs) and interpret it
such that anything in the last bio beyond that limit is ignored.

As some bios can be less than one sector - as happens when a SCSI
sense command is being submitted - we need to set hard_nr_sectors to
bi_size rounded up in blk_rq_bio_prep, and we need to abort the
rq_for_each_segment loop if _iter.bio becomes NULL even if _iter.size
is still non-zero

Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
./block/ll_rw_blk.c | 11 +++++------
./include/linux/bio.h | 9 +++++----
./include/linux/blkdev.h | 11 +++++++----
3 files changed, 17 insertions(+), 14 deletions(-)

diff .prev/block/ll_rw_blk.c ./block/ll_rw_blk.c
--- .prev/block/ll_rw_blk.c 2007-07-31 11:21:14.000000000 +1000
+++ ./block/ll_rw_blk.c 2007-07-31 11:21:15.000000000 +1000
@@ -3364,12 +3364,10 @@ static void blk_recalc_rq_sectors(struct

/*
* if total number of sectors is less than the first segment
- * size, something has gone terribly wrong
+ * size, then we have hit an early end-of-request.
*/
- if (rq->nr_sectors < rq->current_nr_sectors) {
- printk("blk: request botched\n");
- rq->nr_sectors = rq->current_nr_sectors;
- }
+ if (rq->nr_sectors < rq->current_nr_sectors)
+ rq->current_nr_sectors = rq->nr_sectors;
}
}

@@ -3661,7 +3659,8 @@ static void blk_rq_bio_prep(struct reque
/* first two bits are identical in rq->cmd_flags and bio->bi_rw */
rq->cmd_flags |= (bio->bi_rw & 3);

- rq->hard_nr_sectors = rq->nr_sectors = bio_sectors(bio);
+ rq->hard_nr_sectors = rq->nr_sectors
+ = DIV_ROUND_UP(bio->bi_size, 512);
rq->data_len = bio->bi_size;

rq->first_offset = 0;
diff .prev/include/linux/bio.h ./include/linux/bio.h
--- .prev/include/linux/bio.h 2007-07-31 11:21:07.000000000 +1000
+++ ./include/linux/bio.h 2007-07-31 11:21:15.000000000 +1000
@@ -222,7 +222,8 @@ struct bio_iterator {

/* This macro probably need some explanation...
* Its purpose is to find all the effective segments in a bio
- * missing the first 'offs' bytes. We need to be sure to honour
+ * missing the first 'offs' bytes and only covering the next _size
+ * bytes. We need to be sure to honour
* bi_offset which can cause us to skip part of the firs segment,
* and bi_size which may cause us to stop before the end of bi_io_vec.
* The 'for' loop iterates through the segments in bi_io_vec until
@@ -233,9 +234,9 @@ struct bio_iterator {
* follows this macro) if the size would be zero.
* It also keeps 'offset' and 'size' (in the iterator) up to date.
*/
-#define bio_for_each_segment_offset(bv, bio, _i, offs) \
+#define bio_for_each_segment_offset(bv, bio, _i, offs, _size) \
for (_i.i = 0, _i.offset = (bio)->bi_offset + offs, \
- _i.size = (bio)->bi_size - offs; \
+ _i.size = min_t(int, _size, (bio)->bi_size - offs); \
_i.i < (bio)->bi_vcnt && _i.size > 0; \
_i.i++) \
if (bv = *bio_iovec_idx((bio), _i.i), \
@@ -251,7 +252,7 @@ struct bio_iterator {
bv.bv_len > 0)))

#define bio_for_each_segment(bv, bio, __i) \
- bio_for_each_segment_offset(bv, bio, __i, 0)
+ bio_for_each_segment_offset(bv, bio, __i, 0, (bio)->bi_size)
/*
* get a reference to a bio, so it won't disappear. the intended use is
* something like:
diff .prev/include/linux/blkdev.h ./include/linux/blkdev.h
--- .prev/include/linux/blkdev.h 2007-07-31 11:21:14.000000000 +1000
+++ ./include/linux/blkdev.h 2007-07-31 11:21:15.000000000 +1000
@@ -657,13 +657,16 @@ struct req_iterator {
struct bio_iterator i;
struct bio *bio;
int offset;
+ int size;
};
#define rq_for_each_segment(rq, _iter, bvec) \
- for (_iter.bio = (rq)->bio, _iter.offset = (rq)->first_offset; \
- _iter.bio && _iter.bio != rq->biotail->bi_next; \
- _iter.bio = _iter.bio->bi_next, _iter.offset = 0) \
+ for (_iter.bio = (rq)->bio, _iter.offset = (rq)->first_offset, \
+ _iter.size = (rq)->hard_nr_sectors << 9; \
+ _iter.size && _iter.bio; \
+ _iter.size -= (_iter.bio->bi_size - _iter.offset), \
+ _iter.bio = _iter.bio->bi_next, _iter.offset = 0) \
bio_for_each_segment_offset(bvec, _iter.bio, _iter.i, \
- _iter.offset)
+ _iter.offset, _iter.size)

#define rq_iter_last(rq, _iter) ((_iter.bio->bi_next == NULL || \
_iter.bio == rq->biotail) && \
-
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