ocfs2: make ocfs2_adjust_resv_from_alloc simple.

When we allocate some bits from the reservation, we always
allocate from the r_start(see ocfs2_resmap_resv_bits).
So there should be no reason to check between r_start
and start. And I don't think we will change this behaviour
later by allocating from some bits after r_start.  Why not make
ocfs2_adjust_resv_from_alloc simple for now?

The only chance we have to adjust the reservation is when we haven't
reached the end. With this patch, the function is more readable.

Note:
btw, this patch also fixes an original bug in the function
which I haven't found before.
	if (end < ocfs2_resv_end(resv))
		rhs = end - ocfs2_resv_end(resv);
This code is of course buggy. ;)

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Acked-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

2 files changed, 14 insertions, 21 deletions

diff --git a/fs/ocfs2/reservations.c b/fs/ocfs2/reservations.c
index 6497bcc00fa5..cb813ef98846 100644
--- a/fs/ocfs2/reservations.c
+++ b/fs/ocfs2/reservations.c
@@ -408,7 +408,7 @@ ocfs2_find_resv_lhs(struct ocfs2_reservation_map *resmap, unsigned int goal)
  * The start value of *rstart is insignificant.
  *
  * This function searches the bitmap range starting at search_start
- * with length csearch_len for a set of contiguous free bits. We try
+ * with length search_len for a set of contiguous free bits. We try
  * to find up to 'wanted' bits, but can sometimes return less.
  *
  * Returns the length of allocation, 0 if no free bits are found.
@@ -778,38 +778,28 @@ static void
                                      struct ocfs2_alloc_reservation *resv,
                                      unsigned int start, unsigned int end)
 {
-        unsigned int lhs = 0, rhs = 0;
+        unsigned int rhs = 0;
+        unsigned int old_end = ocfs2_resv_end(resv);
 
-        BUG_ON(start < resv->r_start);
+        BUG_ON(start != resv->r_start || old_end < end);
 
         /*
          * Completely used? We can remove it then.
          */
-        if (ocfs2_resv_end(resv) <= end && resv->r_start >= start) {
+        if (old_end == end) {
                 __ocfs2_resv_discard(resmap, resv);
                 return;
         }
 
-        if (end < ocfs2_resv_end(resv))
-                rhs = end - ocfs2_resv_end(resv);
-
-        if (start > resv->r_start)
-                lhs = start - resv->r_start;
+        rhs = old_end - end;
 
         /*
-         * This should have been trapped above. At the very least, rhs
-         * should be non zero.
+         * This should have been trapped above.
          */
-        BUG_ON(rhs == 0 && lhs == 0);
-
-        if (rhs >= lhs) {
-                unsigned int old_end = ocfs2_resv_end(resv);
+        BUG_ON(rhs == 0);
 
-                resv->r_start = end + 1;
-                resv->r_len = old_end - resv->r_start + 1;
-        } else {
-                resv->r_len = start - resv->r_start;
-        }
+        resv->r_start = end + 1;
+        resv->r_len = old_end - resv->r_start + 1;
 }
 
 void ocfs2_resmap_claimed_bits(struct ocfs2_reservation_map *resmap,
@@ -824,6 +814,8 @@ void ocfs2_resmap_claimed_bits(struct ocfs2_reservation_map *resmap,
         if (resv == NULL)
                 return;
 
+        BUG_ON(cstart != resv->r_start);
+
         spin_lock(&resv_lock);
 
         mlog(0, "claim bits: cstart: %u cend: %u clen: %u r_start: %u "
diff --git a/fs/ocfs2/reservations.h b/fs/ocfs2/reservations.h
index 25b0c0e31e91..1e49cc29d06c 100644
--- a/fs/ocfs2/reservations.h
+++ b/fs/ocfs2/reservations.h
@@ -149,7 +149,8 @@ int ocfs2_resmap_resv_bits(struct ocfs2_reservation_map *resmap,
  * reservation. But we must always call this function when bits are claimed.
  * Internally, the reservations code will use this information to mark the
  * reservations bitmap. If resv is passed, it's next allocation window will be
- * calculated.
+ * calculated. It also expects that 'cstart' is the same as we passed back
+ * from ocfs2_resmap_resv_bits().
  */
 void ocfs2_resmap_claimed_bits(struct ocfs2_reservation_map *resmap,
                                struct ocfs2_alloc_reservation *resv,