[PATCH] block: makes bio_split support bio without data

[NeilBrown]

Hi Jens,
 this patch has been sitting in my -next tree for a little while and I was
 hoping for it to go in for the next merge window.
 It simply allows bio_split() to be used on bios without a payload, such as
 'discard'.
 Are you happy with it going in though my 'md' tree, or would you rather take
 it though your 'block' tree?

Thanks,
NeilBrown


From: Shaohua Li <s...@fusionio.com>
Date: Thu, 20 Sep 2012 09:36:03 +1000
Subject: [PATCH] block: makes bio_split support bio without data

discard bio hasn't data attached. We hit a BUG_ON with such bio. This makes
bio_split works for such bio.

Signed-off-by: Shaohua Li <s...@fusionio.com>
Signed-off-by: NeilBrown <ne...@suse.de>

diff --git a/fs/bio.c b/fs/bio.c
index 71072ab..dbb7a6c 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1501,7 +1501,7 @@ struct bio_pair *bio_split(struct bio *bi, int 
first_sectors)
        trace_block_split(bdev_get_queue(bi->bi_bdev), bi,
                                bi->bi_sector + first_sectors);
 
-       BUG_ON(bi->bi_vcnt != 1);
+       BUG_ON(bi->bi_vcnt != 1 && bi->bi_vcnt != 0);
        BUG_ON(bi->bi_idx != 0);
        atomic_set(&bp->cnt, 3);
        bp->error = 0;
@@ -1511,17 +1511,19 @@ struct bio_pair *bio_split(struct bio *bi, int 
first_sectors)
        bp->bio2.bi_size -= first_sectors << 9;
        bp->bio1.bi_size = first_sectors << 9;
 
-       bp->bv1 = bi->bi_io_vec[0];
-       bp->bv2 = bi->bi_io_vec[0];
-       bp->bv2.bv_offset += first_sectors << 9;
-       bp->bv2.bv_len -= first_sectors << 9;
-       bp->bv1.bv_len = first_sectors << 9;
+       if (bi->bi_vcnt != 0) {
+               bp->bv1 = bi->bi_io_vec[0];
+               bp->bv2 = bi->bi_io_vec[0];
+               bp->bv2.bv_offset += first_sectors << 9;
+               bp->bv2.bv_len -= first_sectors << 9;
+               bp->bv1.bv_len = first_sectors << 9;
 
-       bp->bio1.bi_io_vec = &bp->bv1;
-       bp->bio2.bi_io_vec = &bp->bv2;
+               bp->bio1.bi_io_vec = &bp->bv1;
+               bp->bio2.bi_io_vec = &bp->bv2;
 
-       bp->bio1.bi_max_vecs = 1;
-       bp->bio2.bi_max_vecs = 1;
+               bp->bio1.bi_max_vecs = 1;
+               bp->bio2.bi_max_vecs = 1;
+       }
 
        bp->bio1.bi_end_io = bio_pair_end_1;
        bp->bio2.bi_end_io = bio_pair_end_2;

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