block: Consolidate duplicated bio_trim() implementations

Someone cut and pasted md's md_trim_bio() into xen-blkfront.c. Come on,
we should know better than this.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Neil Brown <neilb@suse.de>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 46 insertions, 0 deletions

diff --git a/fs/bio.c b/fs/bio.c
index ea5035d..2bdb4e2 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1805,6 +1805,52 @@ struct bio_pair *bio_split(struct bio *bi, int first_sectors)
 EXPORT_SYMBOL(bio_split);
 
 /**
+ * bio_trim - trim a bio
+ * @bio:	bio to trim
+ * @offset:	number of sectors to trim from the front of @bio
+ * @size:	size we want to trim @bio to, in sectors
+ */
+void bio_trim(struct bio *bio, int offset, int size)
+{
+	/* 'bio' is a cloned bio which we need to trim to match
+	 * the given offset and size.
+	 * This requires adjusting bi_sector, bi_size, and bi_io_vec
+	 */
+	int i;
+	struct bio_vec *bvec;
+	int sofar = 0;
+
+	size <<= 9;
+	if (offset == 0 && size == bio->bi_size)
+		return;
+
+	clear_bit(BIO_SEG_VALID, &bio->bi_flags);
+
+	bio_advance(bio, offset << 9);
+
+	bio->bi_size = size;
+
+	/* avoid any complications with bi_idx being non-zero*/
+	if (bio->bi_idx) {
+		memmove(bio->bi_io_vec, bio->bi_io_vec+bio->bi_idx,
+			(bio->bi_vcnt - bio->bi_idx) * sizeof(struct bio_vec));
+		bio->bi_vcnt -= bio->bi_idx;
+		bio->bi_idx = 0;
+	}
+	/* Make sure vcnt and last bv are not too big */
+	bio_for_each_segment(bvec, bio, i) {
+		if (sofar + bvec->bv_len > size)
+			bvec->bv_len = size - sofar;
+		if (bvec->bv_len == 0) {
+			bio->bi_vcnt = i;
+			break;
+		}
+		sofar += bvec->bv_len;
+	}
+}
+EXPORT_SYMBOL_GPL(bio_trim);
+
+/**
  *      bio_sector_offset - Find hardware sector offset in bio
  *      @bio:           bio to inspect
  *      @index:         bio_vec index