scsi: Adjust return values from processLU

https://bugzilla.redhat.com/show_bug.cgi?id=1171933

Adjust the processLU error returns to be a bit more logical. Currently,
the calling code cannot determine the difference between a non disk/lun
volume and a processed/found disk/lun. It can also not differentiate
between perhaps real/fatal error and one that won't necessarily stop
the code from finding other volumes.

After this patch virStorageBackendSCSIFindLUsInternal will stop processing
as soon as a "fatal" message occurs rather than continuting processing
for no apparent reason. It will also only set the *found value when
at least one of the processLU's was successful.

With the failed return, if the reason for the stop was that the pool
target path did not exist, was /dev, was /dev/, or did not start with
/dev, then iSCSI pool startup and refresh will fail.

src/storage/storage_backend_scsi.c

@@ -377,6 +377,15 @@ getBlockDevice(uint32_t host,
 }
 
 
+/*
+ * Process a Logical Unit entry from the scsi host device directory
+ *
+ * Returns:
+ *
+ *  0  => Found a valid entry
+ *  -1 => Some sort of fatal error
+ *  -2 => non-fatal error or a non-disk entry
+ */
 static int
 processLU(virStoragePoolObjPtr pool,
           uint32_t host,
@@ -395,7 +404,7 @@ processLU(virStoragePoolObjPtr pool,
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("Failed to determine if %u:%u:%u:%u is a Direct-Access LUN"),
                        host, bus, target, lun);
-        goto out;
+        return -1;
     }
 
     /* We don't create volumes for devices other than disk and cdrom
@@ -403,32 +412,28 @@ processLU(virStoragePoolObjPtr pool,
      * isn't an error, either. */
     if (!(device_type == VIR_STORAGE_DEVICE_TYPE_DISK ||
           device_type == VIR_STORAGE_DEVICE_TYPE_ROM))
-    {
-        retval = 0;
-        goto out;
-    }
+        return -2;
 
     VIR_DEBUG("%u:%u:%u:%u is a Direct-Access LUN",
               host, bus, target, lun);
 
     if (getBlockDevice(host, bus, target, lun, &block_device) < 0) {
         VIR_DEBUG("Failed to find block device for this LUN");
-        goto out;
+        return -1;
     }
 
-    if (virStorageBackendSCSINewLun(pool,
-                                    host, bus, target, lun,
-                                    block_device) < 0) {
+    retval = virStorageBackendSCSINewLun(pool, host, bus, target, lun,
+                                         block_device);
+    if (retval < 0) {
         VIR_DEBUG("Failed to create new storage volume for %u:%u:%u:%u",
                   host, bus, target, lun);
-        goto out;
+        goto cleanup;
     }
-    retval = 0;
 
     VIR_DEBUG("Created new storage volume for %u:%u:%u:%u successfully",
               host, bus, target, lun);
 
- out:
+ cleanup:
     VIR_FREE(block_device);
     return retval;
 }
@@ -461,6 +466,8 @@ virStorageBackendSCSIFindLUs(virStoragePoolObjPtr pool,
     snprintf(devicepattern, sizeof(devicepattern), "%u:%%u:%%u:%%u\n", scanhost);
 
     while ((retval = virDirRead(devicedir, &lun_dirent, device_path)) > 0) {
+        int rc;
+
         if (sscanf(lun_dirent->d_name, devicepattern,
                    &bus, &target, &lun) != 3) {
             continue;
@@ -468,7 +475,12 @@ virStorageBackendSCSIFindLUs(virStoragePoolObjPtr pool,
 
         VIR_DEBUG("Found possible LU '%s'", lun_dirent->d_name);
 
-        if (processLU(pool, scanhost, bus, target, lun) == 0)
+        rc = processLU(pool, scanhost, bus, target, lun);
+        if (rc == -1) {
+            retval = -1;
+            break;
+        }
+        if (rc == 0)
             found++;
     }