Add FSYNC_VerifyCheckout

Add the function FSYNC_VerifyCheckout, which can be used to verify that
a previous checkout of a volume is still known by the fileserver, and
hasn't been forgotten about (by e.g. the fileserver restarting).

Change-Id: Ie3ec63d155fe16ca4929b370bbe55850075cec83
Reviewed-on: http://gerrit.openafs.org/1404
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>

diff --git a/src/vol/fssync-client.c b/src/vol/fssync-client.c
index 0520c00..4fa6448 100644 (file)
--- a/src/vol/fssync-client.c
+++ b/src/vol/fssync-client.c
@@ -208,6 +208,99 @@ FSYNC_VolOp(VolumeId volume, char * partition,
     return FSYNC_GenericOp(&vcom, sizeof(vcom), command, reason, res);
 }
 
+/**
+ * verify that the fileserver still thinks we have a volume checked out.
+ *
+ * In DAFS, a non-fileserver program accesses a volume by checking it out from
+ * the fileserver (FSYNC_VOL_OFF or FSYNC_VOL_NEEDVOLUME), and then locks the
+ * volume. There is a possibility that the fileserver crashes or restarts for
+ * some reason between volume checkout and locking; if this happens, the
+ * fileserver could attach the volume before we had a chance to lock it. This
+ * function serves to detect if this has happened; it must be called after
+ * volume checkout and locking to make sure the fileserver still thinks we
+ * have the volume. (If it doesn't, we should try to check it out again.)
+ *
+ * @param[in] volume    volume ID
+ * @param[in] partition partition name string
+ * @param[in] command   the command that was used to checkout the volume
+ * @param[in] reason    the reason code used to checkout the volume
+ *
+ * @return operation status
+ *  @retval SYNC_OK the fileserver could not have attached the volume since
+ *                  it was checked out (either it thinks it is still checked
+ *                  out, or it doesn't know about the volume)
+ *  @retval SYNC_DENIED fileserver may have restarted since checkout; checkout
+ *                      should be reattempted
+ *  @retval SYNC_COM_ERROR internal/fatal error
+ */
+afs_int32
+FSYNC_VerifyCheckout(VolumeId volume, char * partition,
+                     afs_int32 command, afs_int32 reason)
+{
+    SYNC_response res;
+    FSSYNC_VolOp_info vop;
+    afs_int32 code;
+    afs_int32 pid;
+
+    res.hdr.response_len = sizeof(res.hdr);
+    res.payload.buf = &vop;
+    res.payload.len = sizeof(vop);
+
+    code = FSYNC_VolOp(volume, partition, FSYNC_VOL_QUERY_VOP, FSYNC_WHATEVER, &res);
+    if (code != SYNC_OK) {
+       if (res.hdr.reason == FSYNC_NO_PENDING_VOL_OP) {
+           Log("FSYNC_VerifyCheckout: fileserver claims no vop for vol %lu "
+               "part %s; fileserver may have restarted since checkout\n",
+               afs_printable_uint32_lu(volume), partition);
+           return SYNC_DENIED;
+       }
+
+       if (res.hdr.reason == FSYNC_UNKNOWN_VOLID) {
+           /* if the fileserver does not know about this volume, there's no
+            * way it could have attached it, so we're fine */
+           return SYNC_OK;
+       }
+
+       Log("FSYNC_VerifyCheckout: FSYNC_VOL_QUERY_VOP failed for vol %lu "
+           "part %s with code %ld reason %ld\n",
+           afs_printable_uint32_lu(volume), partition,
+           afs_printable_int32_ld(code),
+           afs_printable_int32_ld(res.hdr.reason));
+       return SYNC_COM_ERROR;
+    }
+
+    pid = getpid();
+
+    /* Check if the current vol op is us. Checking pid is probably enough, but
+     * be a little bit paranoid. We could also probably check tid, but I'm not
+     * completely confident of its reliability on all platforms (on pthread
+     * envs, we coerce a pthread_t to an afs_int32, which is not guaranteed
+     * to mean anything significant). */
+
+    if (vop.com.programType == programType && vop.com.pid == pid &&
+        vop.com.command == command && vop.com.reason == reason) {
+
+       /* looks like the current pending vol op is the same one as the one
+        * with which we checked it out. success. */
+       return SYNC_OK;
+    }
+
+    Log("FSYNC_VerifyCheckout: vop for vol %lu part %s does not match "
+        "expectations (got pt %ld pid %ld cmd %ld reason %ld, but expected "
+        "pt %ld pid %ld cmd %ld reason %ld); fileserver may have restarted "
+        "since checkout\n", afs_printable_uint32_lu(volume), partition,
+       afs_printable_int32_ld(vop.com.programType),
+       afs_printable_int32_ld(vop.com.pid),
+       afs_printable_int32_ld(vop.com.command),
+       afs_printable_int32_ld(vop.com.reason),
+       afs_printable_int32_ld(programType),
+       afs_printable_int32_ld(pid),
+       afs_printable_int32_ld(command),
+       afs_printable_int32_ld(reason));
+
+    return SYNC_DENIED;
+}
+
 afs_int32
 FSYNC_StatsOp(FSSYNC_StatsOp_hdr * scom, int command, int reason,
              SYNC_response * res)

diff --git a/src/vol/fssync.h b/src/vol/fssync.h
index 9e49a5b..638c743 100644 (file)
--- a/src/vol/fssync.h
+++ b/src/vol/fssync.h
@@ -226,4 +226,7 @@ extern afs_int32 FSYNC_VGCDel(char *part, VolumeId parent, VolumeId child,
                              int reason, SYNC_response *res);
 extern afs_int32 FSYNC_VGCScan(char *part, int reason);
 
+extern afs_int32 FSYNC_VerifyCheckout(VolumeId volume, char *partition,
+                                      afs_int32 command, afs_int32 reason);
+
 #endif /* __fssync_h_ */