+/**
+ * is_last_bud - check if the bud is the last in the journal head.
+ * @c: UBIFS file-system description object
+ * @bud: bud description object
+ *
+ * This function checks if bud @bud is the last bud in its journal head. This
+ * information is then used by 'replay_bud()' to decide whether the bud can
+ * have corruptions or not. Indeed, only last buds can be corrupted by power
+ * cuts. Returns %1 if this is the last bud, and %0 if not.
+ */
+static int is_last_bud(struct ubifs_info *c, struct ubifs_bud *bud)
+{
+ struct ubifs_jhead *jh = &c->jheads[bud->jhead];
+ struct ubifs_bud *next;
+ uint32_t data;
+ int err;
+
+ if (list_is_last(&bud->list, &jh->buds_list))
+ return 1;
+
+ /*
+ * The following is a quirk to make sure we work correctly with UBIFS
+ * images used with older UBIFS.
+ *
+ * Normally, the last bud will be the last in the journal head's list
+ * of bud. However, there is one exception if the UBIFS image belongs
+ * to older UBIFS. This is fairly unlikely: one would need to use old
+ * UBIFS, then have a power cut exactly at the right point, and then
+ * try to mount this image with new UBIFS.
+ *
+ * The exception is: it is possible to have 2 buds A and B, A goes
+ * before B, and B is the last, bud B is contains no data, and bud A is
+ * corrupted at the end. The reason is that in older versions when the
+ * journal code switched the next bud (from A to B), it first added a
+ * log reference node for the new bud (B), and only after this it
+ * synchronized the write-buffer of current bud (A). But later this was
+ * changed and UBIFS started to always synchronize the write-buffer of
+ * the bud (A) before writing the log reference for the new bud (B).
+ *
+ * But because older UBIFS always synchronized A's write-buffer before
+ * writing to B, we can recognize this exceptional situation but
+ * checking the contents of bud B - if it is empty, then A can be
+ * treated as the last and we can recover it.
+ *
+ * TODO: remove this piece of code in a couple of years (today it is
+ * 16.05.2011).
+ */
+ next = list_entry(bud->list.next, struct ubifs_bud, list);
+ if (!list_is_last(&next->list, &jh->buds_list))
+ return 0;
+
+ err = ubifs_leb_read(c, next->lnum, (char *)&data, next->start, 4, 1);
+ if (err)
+ return 0;
+
+ return data == 0xFFFFFFFF;
+}
+