dm: preserve bi_io_vec when resubmitting bios

Device mapper saves and restores various fields in the bio, but it doesn't save
bi_io_vec. If the device driver modifies this after a partially successful
request, dm-raid1 and dm-multipath may attempt to resubmit a bio that has
bi_size inconsistent with the size of vector.

To make requests resubmittable in dm-raid1 and dm-multipath, we must save
and restore the bio vector as well.

To reduce the memory overhead involved in this, we do not save the pages in a
vector and use a 16-bit field size if the page size is less than 65536.

Cc: [e-mail]
Signed-off-by: Mikulas Patocka <[e-mail]>
Signed-off-by: Alasdair G Kergon <[e-mail]>

drivers/md/dm-bio-record.h

···
  * functions in this file help the target record and restore the
  * original bio state.
  */
+
+struct dm_bio_vec_details {
+#if PAGE_SIZE < 65536
+	__u16 bv_len;
+	__u16 bv_offset;
+#else
+	unsigned bv_len;
+	unsigned bv_offset;
+#endif
+};
+
 struct dm_bio_details {
 	sector_t bi_sector;
 	struct block_device *bi_bdev;
 	unsigned int bi_size;
 	unsigned short bi_idx;
 	unsigned long bi_flags;
+	struct dm_bio_vec_details bi_io_vec[BIO_MAX_PAGES];
 };
 
 static inline void dm_bio_record(struct dm_bio_details *bd, struct bio *bio)
 {
+	unsigned i;
+
 	bd->bi_sector = bio->bi_sector;
 	bd->bi_bdev = bio->bi_bdev;
 	bd->bi_size = bio->bi_size;
 	bd->bi_idx = bio->bi_idx;
 	bd->bi_flags = bio->bi_flags;
+
+	for (i = 0; i < bio->bi_vcnt; i++) {
+		bd->bi_io_vec[i].bv_len = bio->bi_io_vec[i].bv_len;
+		bd->bi_io_vec[i].bv_offset = bio->bi_io_vec[i].bv_offset;
+	}
 }
 
 static inline void dm_bio_restore(struct dm_bio_details *bd, struct bio *bio)
 {
+	unsigned i;
+
 	bio->bi_sector = bd->bi_sector;
 	bio->bi_bdev = bd->bi_bdev;
 	bio->bi_size = bd->bi_size;
 	bio->bi_idx = bd->bi_idx;
 	bio->bi_flags = bd->bi_flags;
+
+	for (i = 0; i < bio->bi_vcnt; i++) {
+		bio->bi_io_vec[i].bv_len = bd->bi_io_vec[i].bv_len;
+		bio->bi_io_vec[i].bv_offset = bd->bi_io_vec[i].bv_offset;
+	}
 }
 
 #endif