1 files changed, 123 insertions, 0 deletions
diff --git a/fs/gfs2/recovery.c b/fs/gfs2/recovery.c
index 7389e445a7a7..2dac43065382 100644
--- a/fs/gfs2/recovery.c
+++ b/fs/gfs2/recovery.c
@@ -182,6 +182,129 @@ static int get_log_header(struct gfs2_jdesc *jd, unsigned int blk,
 }
 
 /**
+ * find_good_lh - find a good log header
+ * @jd: the journal
+ * @blk: the segment to start searching from
+ * @lh: the log header to fill in
+ * @forward: if true search forward in the log, else search backward
+ *
+ * Call get_log_header() to get a log header for a segment, but if the
+ * segment is bad, either scan forward or backward until we find a good one.
+ *
+ * Returns: errno
+ */
+
+static int find_good_lh(struct gfs2_jdesc *jd, unsigned int *blk,
+			struct gfs2_log_header_host *head)
+{
+	unsigned int orig_blk = *blk;
+	int error;
+
+	for (;;) {
+		error = get_log_header(jd, *blk, head);
+		if (error <= 0)
+			return error;
+
+		if (++*blk == jd->jd_blocks)
+			*blk = 0;
+
+		if (*blk == orig_blk) {
+			gfs2_consist_inode(GFS2_I(jd->jd_inode));
+			return -EIO;
+		}
+	}
+}
+
+/**
+ * jhead_scan - make sure we've found the head of the log
+ * @jd: the journal
+ * @head: this is filled in with the log descriptor of the head
+ *
+ * At this point, seg and lh should be either the head of the log or just
+ * before.  Scan forward until we find the head.
+ *
+ * Returns: errno
+ */
+
+static int jhead_scan(struct gfs2_jdesc *jd, struct gfs2_log_header_host *head)
+{
+	unsigned int blk = head->lh_blkno;
+	struct gfs2_log_header_host lh;
+	int error;
+
+	for (;;) {
+		if (++blk == jd->jd_blocks)
+			blk = 0;
+
+		error = get_log_header(jd, blk, &lh);
+		if (error < 0)
+			return error;
+		if (error == 1)
+			continue;
+
+		if (lh.lh_sequence == head->lh_sequence) {
+			gfs2_consist_inode(GFS2_I(jd->jd_inode));
+			return -EIO;
+		}
+		if (lh.lh_sequence < head->lh_sequence)
+			break;
+
+		*head = lh;
+	}
+
+	return 0;
+}
+
+/**
+ * gfs2_find_jhead - find the head of a log
+ * @jd: the journal
+ * @head: the log descriptor for the head of the log is returned here
+ *
+ * Do a binary search of a journal and find the valid log entry with the
+ * highest sequence number.  (i.e. the log head)
+ *
+ * Returns: errno
+ */
+
+int gfs2_find_jhead(struct gfs2_jdesc *jd, struct gfs2_log_header_host *head)
+{
+	struct gfs2_log_header_host lh_1, lh_m;
+	u32 blk_1, blk_2, blk_m;
+	int error;
+
+	blk_1 = 0;
+	blk_2 = jd->jd_blocks - 1;
+
+	for (;;) {
+		blk_m = (blk_1 + blk_2) / 2;
+
+		error = find_good_lh(jd, &blk_1, &lh_1);
+		if (error)
+			return error;
+
+		error = find_good_lh(jd, &blk_m, &lh_m);
+		if (error)
+			return error;
+
+		if (blk_1 == blk_m || blk_m == blk_2)
+			break;
+
+		if (lh_1.lh_sequence <= lh_m.lh_sequence)
+			blk_1 = blk_m;
+		else
+			blk_2 = blk_m;
+	}
+
+	error = jhead_scan(jd, &lh_1);
+	if (error)
+		return error;
+
+	*head = lh_1;
+
+	return error;
+}
+
+/**
  * foreach_descriptor - go through the active part of the log
  * @jd: the journal
  * @start: the first log header in the active region