+/**
+ * map_journal_extents - create a reusable "extent" mapping from all logical
+ * blocks to all physical blocks for the given journal. This will save
+ * us time when writing journal blocks. Most journals will have only one
+ * extent that maps all their logical blocks. That's because gfs2.mkfs
+ * arranges the journal blocks sequentially to maximize performance.
+ * So the extent would map the first block for the entire file length.
+ * However, gfs2_jadd can happen while file activity is happening, so
+ * those journals may not be sequential. Less likely is the case where
+ * the users created their own journals by mounting the metafs and
+ * laying it out. But it's still possible. These journals might have
+ * several extents.
+ *
+ * TODO: This should be done in bigger chunks rather than one block at a time,
+ * but since it's only done at mount time, I'm not worried about the
+ * time it takes.
+ */
+static int map_journal_extents(struct gfs2_sbd *sdp)
+{
+ struct gfs2_jdesc *jd = sdp->sd_jdesc;
+ unsigned int lb;
+ u64 db, prev_db; /* logical block, disk block, prev disk block */
+ struct gfs2_inode *ip = GFS2_I(jd->jd_inode);
+ struct gfs2_journal_extent *jext = NULL;
+ struct buffer_head bh;
+ int rc = 0;
+
+ prev_db = 0;
+
+ for (lb = 0; lb < ip->i_di.di_size >> sdp->sd_sb.sb_bsize_shift; lb++) {
+ bh.b_state = 0;
+ bh.b_blocknr = 0;
+ bh.b_size = 1 << ip->i_inode.i_blkbits;
+ rc = gfs2_block_map(jd->jd_inode, lb, &bh, 0);
+ db = bh.b_blocknr;
+ if (rc || !db) {
+ printk(KERN_INFO "GFS2 journal mapping error %d: lb="
+ "%u db=%llu\n", rc, lb, (unsigned long long)db);
+ break;
+ }
+ if (!prev_db || db != prev_db + 1) {
+ jext = kzalloc(sizeof(struct gfs2_journal_extent),
+ GFP_KERNEL);
+ if (!jext) {
+ printk(KERN_INFO "GFS2 error: out of memory "
+ "mapping journal extents.\n");
+ rc = -ENOMEM;
+ break;
+ }
+ jext->dblock = db;
+ jext->lblock = lb;
+ jext->blocks = 1;
+ list_add_tail(&jext->extent_list, &jd->extent_list);
+ } else {
+ jext->blocks++;
+ }
+ prev_db = db;
+ }
+ return rc;
+}
+