1 files changed, 46 insertions, 0 deletions

diff --git a/fs/bio.c b/fs/bio.c
index ea5035da4d9a..2bdb4e25ee77 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