vol: fix nextVnodeUnique roll over

Fixes for the per volume nextVnodeUnique counter roll over. Uniquifier number 1
is reserved for the root vnode, so reset the unique count to 2 when the
nextVnodeUnique counter rolls over.

Update the disk backed V_uniquifier count when the in-memory nextVnodeUnique
counter rolls over during the creation of a new vnode. If the nextVnodeUnique
rolls over when V_uniquifier is UINT32_MAX, then the V_uniquifier is not updated
and remains at UINT32_MAX until the next VUpdateVolume_r() call for the volume.

This bug is usually masked by the VBumpVolumeUsage(), which on every 128 volume
accesses, bumps the V_uniquifier to be 200 more than the current
nextVnodeUnique counter.  This causes the V_uniquifier to roll over before
reaching UINT32_MAX.  (The number of access before updating the headers is set
in the usage_threshold volume package option, which is currently set to 128 by
default.)

The following shows the unique counters for a series of vnode
creation/deletions before this commit.  The nextVnodeUnique rolls over to 1,
and the uniquifier is not reset.  The `usage_threshold' was set to a value
greater than 200 to avoid the VBumpVolumeUsage() calls during this test run.

fid = 536870918.4.4294967294, nextVnodeUnique = 4294967295, uniquifier = 4294967295
fid = 536870918.4.4294967295, nextVnodeUnique = 0, uniquifier = 4294967295
fid = 536870918.4.1, nextVnodeUnique = 2, uniquifier = 4294967295
fid = 536870918.4.2, nextVnodeUnique = 3, uniquifier = 4294967295

The following shows the unique counters after this commit:

fid = 536870918.4.4294967294, nextVnodeUnique = 4294967295, uniquifier = 4294967295
fid = 536870918.4.4294967295, nextVnodeUnique = 0, uniquifier = 4294967295
fid = 536870918.4.2, nextVnodeUnique = 3, uniquifier = 203
fid = 536870918.4.3, nextVnodeUnique = 4, uniquifier = 203

Change-Id: I438670200bf97baeac1486eda7df4cf243aabfc4
Reviewed-on: http://gerrit.openafs.org/10616
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/vnode.c b/src/vol/vnode.c
index 6983e8d..9eb120d 100644 (file)
--- a/src/vol/vnode.c
+++ b/src/vol/vnode.c
@@ -651,11 +651,16 @@ VAllocVnode_r(Error * ec, Volume * vp, VnodeType type, VnodeId in_vnode, Unique
      */
 
     if (!in_vnode) {
+       int rollover = 0;
+
        unique = vp->nextVnodeUnique++;
-       if (!unique)
+       if (unique == 0) {
+           rollover = 1;       /* nextVnodeUnique rolled over */
+           vp->nextVnodeUnique = 2;    /* 1 is reserved for the root vnode */
            unique = vp->nextVnodeUnique++;
+       }
 
-       if (vp->nextVnodeUnique > V_uniquifier(vp)) {
+       if (vp->nextVnodeUnique > V_uniquifier(vp) || rollover) {
            VUpdateVolume_r(ec, vp, 0);
            if (*ec)
                return NULL;