UBIFS: split ubifs_rcvry_gc_commit

Split the 'ubifs_rcvry_gc_commit()' function and introduce a 'grab_empty_leb()'
heler. This cleans 'ubifs_rcvry_gc_commit()' a little and makes it a bit less
of spagetti.

Also, add a commentary which explains why it is crucial to first search for an
empty LEB and then run commit.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c
index 3d2598d..11776ae 100644 (file)
--- a/fs/ubifs/recovery.c
+++ b/fs/ubifs/recovery.c
@@ -1070,6 +1070,53 @@ int ubifs_clean_lebs(const struct ubifs_info *c, void *sbuf)
 }
 
 /**
+ * grab_empty_leb - grab an empty LEB to use as GC LEB and run commit.
+ * @c: UBIFS file-system description object
+ *
+ * This is a helper function for 'ubifs_rcvry_gc_commit()' which grabs an empty
+ * LEB to be used as GC LEB (@c->gc_lnum), and then runs the commit. Returns
+ * zero in case of success and a negative error code in case of failure.
+ */
+static int grab_empty_leb(struct ubifs_info *c)
+{
+       int lnum, err;
+
+       /*
+        * Note, it is very important to first search for an empty LEB and then
+        * run the commit, not vice-versa. The reason is that there might be
+        * only one empty LEB at the moment, the one which has been the
+        * @c->gc_lnum just before the power cut happened. During the regular
+        * UBIFS operation (not now) @c->gc_lnum is marked as "taken", so no
+        * one but GC can grab it. But at this moment this single empty LEB is
+        * not marked as taken, so if we run commit - what happens? Right, the
+        * commit will grab it and write the index there. Remember that the
+        * index always expands as long as there is free space, and it only
+        * starts consolidating when we run out of space.
+        *
+        * IOW, if we run commit now, we might not be able to find a free LEB
+        * after this.
+        */
+       lnum = ubifs_find_free_leb_for_idx(c);
+       if (lnum < 0) {
+               dbg_err("could not find an empty LEB");
+               dbg_dump_lprops(c);
+               dbg_dump_budg(c, &c->bi);
+               return lnum;
+       }
+
+       /* Reset the index flag */
+       err = ubifs_change_one_lp(c, lnum, LPROPS_NC, LPROPS_NC, 0,
+                                 LPROPS_INDEX, 0);
+       if (err)
+               return err;
+
+       c->gc_lnum = lnum;
+       dbg_rcvry("found empty LEB %d, run commit", lnum);
+
+       return ubifs_run_commit(c);
+}
+
+/**
  * ubifs_rcvry_gc_commit - recover the GC LEB number and run the commit.
  * @c: UBIFS file-system description object
  *
@@ -1096,7 +1143,7 @@ int ubifs_rcvry_gc_commit(struct ubifs_info *c)
        c->gc_lnum = -1;
        if (wbuf->lnum == -1) {
                dbg_rcvry("no GC head LEB");
-               goto find_free;
+               return grab_empty_leb(c);
        }
        /*
         * See whether the used space in the dirtiest LEB fits in the GC head
@@ -1104,7 +1151,7 @@ int ubifs_rcvry_gc_commit(struct ubifs_info *c)
         */
        if (wbuf->offs == c->leb_size) {
                dbg_rcvry("no room in GC head LEB");
-               goto find_free;
+               return grab_empty_leb(c);
        }
        err = ubifs_find_dirty_leb(c, &lp, wbuf->offs, 2);
        if (err) {
@@ -1121,7 +1168,7 @@ int ubifs_rcvry_gc_commit(struct ubifs_info *c)
                 */
                if (err == -ENOSPC) {
                        dbg_rcvry("could not find a dirty LEB");
-                       goto find_free;
+                       return grab_empty_leb(c);
                }
                return err;
        }
@@ -1167,30 +1214,6 @@ int ubifs_rcvry_gc_commit(struct ubifs_info *c)
                return err;
        dbg_rcvry("allocated LEB %d for GC", lnum);
        return 0;
-
-find_free:
-       /*
-        * There is no GC head LEB or the free space in the GC head LEB is too
-        * small, or there are not dirty LEBs. Allocate gc_lnum by calling
-        * 'ubifs_find_free_leb_for_idx()' so GC is not run.
-        */
-       lnum = ubifs_find_free_leb_for_idx(c);
-       if (lnum < 0) {
-               dbg_err("could not find an empty LEB");
-               dbg_dump_lprops(c);
-               dbg_dump_budg(c, &c->bi);
-               return lnum;
-       }
-       /* And reset the index flag */
-       err = ubifs_change_one_lp(c, lnum, LPROPS_NC, LPROPS_NC, 0,
-                                 LPROPS_INDEX, 0);
-       if (err)
-               return err;
-       c->gc_lnum = lnum;
-       dbg_rcvry("allocated LEB %d for GC", lnum);
-       /* Run the commit */
-       dbg_rcvry("committing");
-       return ubifs_run_commit(c);
 }
 
 /**