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Subject[PATCH 01/11] dm io: fix bi_max_vecs
From: Heinz Mauelshagen <hjm@redhat.com>

The existing code allocates an extra slot in bi_io_vec[] and uses it to
store the region number.

This patch hides the extra slot from bio_add_page() so the region number
can't get overwritten.

Also remove a hard-coded SECTOR_SHIFT and fix a typo in a comment.

Signed-off-by: Heinz Mauelshagen <hjm@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: Milan Broz <mbroz@redhat.com>
Cc: dm-devel@redhat.com

Index: linux-2.6.19-rc6/drivers/md/dm-io.c
===================================================================
--- linux-2.6.19-rc6.orig/drivers/md/dm-io.c 2006-11-22 17:26:47.000000000 +0000
+++ linux-2.6.19-rc6/drivers/md/dm-io.c 2006-11-22 17:26:53.000000000 +0000
@@ -92,12 +92,12 @@ void dm_io_put(unsigned int num_pages)
*---------------------------------------------------------------*/
static inline void bio_set_region(struct bio *bio, unsigned region)
{
- bio->bi_io_vec[bio->bi_max_vecs - 1].bv_len = region;
+ bio->bi_io_vec[bio->bi_max_vecs].bv_len = region;
}

static inline unsigned bio_get_region(struct bio *bio)
{
- return bio->bi_io_vec[bio->bi_max_vecs - 1].bv_len;
+ return bio->bi_io_vec[bio->bi_max_vecs].bv_len;
}

/*-----------------------------------------------------------------
@@ -136,6 +136,7 @@ static int endio(struct bio *bio, unsign
zero_fill_bio(bio);

dec_count(io, bio_get_region(bio), error);
+ bio->bi_max_vecs++;
bio_put(bio);

return 0;
@@ -250,16 +251,18 @@ static void do_region(int rw, unsigned i

while (remaining) {
/*
- * Allocate a suitably sized bio, we add an extra
- * bvec for bio_get/set_region().
+ * Allocate a suitably sized-bio: we add an extra
+ * bvec for bio_get/set_region() and decrement bi_max_vecs
+ * to hide it from bio_add_page().
*/
- num_bvecs = (remaining / (PAGE_SIZE >> 9)) + 2;
+ num_bvecs = (remaining / (PAGE_SIZE >> SECTOR_SHIFT)) + 2;
bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, _bios);
bio->bi_sector = where->sector + (where->count - remaining);
bio->bi_bdev = where->bdev;
bio->bi_end_io = endio;
bio->bi_private = io;
bio->bi_destructor = dm_bio_destructor;
+ bio->bi_max_vecs--;
bio_set_region(bio, region);

/*
@@ -302,7 +305,7 @@ static void dispatch_io(int rw, unsigned
}

/*
- * Drop the extra refence that we were holding to avoid
+ * Drop the extra reference that we were holding to avoid
* the io being completed too early.
*/
dec_count(io, 0, 0);
-
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