Detect if Fibre Channel support exists

This patch adds a simple check to see if the kernel
even supports Fibre Channel before calling systool -c fc_host -v
to find the active HBA's on the system.

The problem is that privsep can't quietly run systool without puking out
a bunch of errors to stderr.  We know that most systems don't have FC and
that's why we always wrapped out call to putils executing systool
with a try block.  putils allows callers to expect exceptions and then
handle the exception logging or not themselves.  privsep doesn't allow that.

Change-Id: Idd254303c9cca2b57d358de2fdbaf8abdd76b553

os_brick/initiator/linuxfc.py

@@ -27,6 +27,14 @@ LOG = logging.getLogger(__name__)
 
 
 class LinuxFibreChannel(linuxscsi.LinuxSCSI):
+
+    def has_fc_support(self):
+        FC_HOST_SYSFS_PATH = '/sys/class/fc_host'
+        if os.path.isdir(FC_HOST_SYSFS_PATH):
+            return True
+        else:
+            return False
+
     def _get_hba_channel_scsi_target(self, hba):
         """Try to get the HBA channel and SCSI target for an HBA.
 
@@ -72,6 +80,13 @@ class LinuxFibreChannel(linuxscsi.LinuxSCSI):
 
     def get_fc_hbas(self):
         """Get the Fibre Channel HBA information."""
+
+        if not self.has_fc_support():
+            # there is no FC support in the kernel loaded
+            # so there is no need to even try to run systool
+            LOG.debug("No Fibre Channel support detected on system.")
+            return []
+
         out = None
         try:
             out, _err = self._execute('systool', '-c', 'fc_host', '-v',

os_brick/tests/initiator/test_linuxfc.py

@@ -27,12 +27,23 @@ class LinuxFCTestCase(base.TestCase):
         self.cmds = []
 
         self.mock_object(os.path, 'exists', return_value=True)
+        self.mock_object(os.path, 'isdir', return_value=True)
         self.lfc = linuxfc.LinuxFibreChannel(None, execute=self.fake_execute)
 
     def fake_execute(self, *cmd, **kwargs):
         self.cmds.append(" ".join(cmd))
         return "", None
 
+    def test_has_fc_support(self):
+
+        self.mock_object(os.path, 'isdir', return_value=False)
+        has_fc = self.lfc.has_fc_support()
+        self.assertFalse(has_fc)
+
+        self.mock_object(os.path, 'isdir', return_value=True)
+        has_fc = self.lfc.has_fc_support()
+        self.assertTrue(has_fc)
+
     def test_rescan_hosts(self):
         # We check that we try to get the HBA channel and SCSI target
         execute_results = (