vol: reset nextVnodeUnique when uniquifier rolls over

The on disk uniquifier counter is set to 200 more than the current
nextVnodeUnique counter when the volume information is updated to disk. When
the nextVnodeUnique is near UINT32_MAX, then the uniquifier counter rolls
over.  This can happen during a volume header update due to
VBumpVolumeUsage_r().

With this change, the nextVnodeUnique customer is reset to 2 and the
uniquifier is reset to 202 when a roll over occurs. (uniquifier of 1 is
reserved for the root vnode.)

With this change, the number of possible uniquifier numbers is limited to
200 less than UINT32_MAX.

The following shows a series of vnode creation/deletions to illustrate
the uniquifier rollover before this commit:

fid = 536870918.4.4294967114, nextVnodeUnique = 4294967115, uniquifier = 4294967295
fid = 536870918.4.4294967115, nextVnodeUnique = 4294967116, uniquifier = 4294967295
fid = 536870918.4.4294967116, nextVnodeUnique = 4294967117, uniquifier = 21
fid = 536870918.4.4294967117, nextVnodeUnique = 4294967118, uniquifier = 22

and after this commit:

fid = 536870918.4.4294967115, nextVnodeUnique = 4294967116, uniquifier = 4294967295
fid = 536870918.4.4294967116, nextVnodeUnique = 2, uniquifier = 202
fid = 536870918.4.2, nextVnodeUnique = 3, uniquifier = 202
fid = 536870918.4.3, nextVnodeUnique = 4, uniquifier = 202

Change-Id: I93c8a7cf47e39b8701265d6507cfc4f8c1352ddc
Reviewed-on: http://gerrit.openafs.org/10617
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>

diff --git a/src/vol/volume.c b/src/vol/volume.c
index d6c2d38..7eb239d 100644 (file)
--- a/src/vol/volume.c
+++ b/src/vol/volume.c
@@ -218,6 +218,12 @@ pthread_t vol_glock_holder = 0;
  */
 #define VOLUME_HASH_REORDER_CHAIN_THRESH (VOLUME_HASH_REORDER_THRESHOLD / 2)
 
+/*
+ * The per volume uniquifier is bumped by 200 and and written to disk
+ * every 200 file creates.
+ */
+#define VOLUME_UPDATE_UNIQUIFIER_BUMP 200
+
 #include "rx/rx_queue.h"
 
 
@@ -4929,10 +4935,20 @@ VUpdateVolume_r(Error * ec, Volume * vp, int flags)
 #endif
 
     *ec = 0;
-    if (programType == fileServer)
-       V_uniquifier(vp) =
-           (V_inUse(vp) ? V_nextVnodeUnique(vp) +
-            200 : V_nextVnodeUnique(vp));
+    if (programType == fileServer) {
+       if (!V_inUse(vp)) {
+           V_uniquifier(vp) = V_nextVnodeUnique(vp);
+       } else {
+           V_uniquifier(vp) =
+               V_nextVnodeUnique(vp) + VOLUME_UPDATE_UNIQUIFIER_BUMP;
+           if (V_uniquifier(vp) < V_nextVnodeUnique(vp)) {
+               /* uniquifier rolled over; reset the counters */
+               V_nextVnodeUnique(vp) = 2;      /* 1 is reserved for the root vnode */
+               V_uniquifier(vp) =
+                   V_nextVnodeUnique(vp) + VOLUME_UPDATE_UNIQUIFIER_BUMP;
+           }
+       }
+    }
 
 #ifdef AFS_DEMAND_ATTACH_FS
     state_save = VChangeState_r(vp, VOL_STATE_UPDATING);