utils: Implement virCommandPassFDGetFDIndex

Implement virCommandPassFDGetFDIndex to determine the index a given
file descriptor will have when passed to the child process.
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>

src/libvirt_private.syms

@@ -1214,6 +1214,7 @@ virCommandNewArgList;
 virCommandNewArgs;
 virCommandNonblockingFDs;
 virCommandPassFD;
+virCommandPassFDGetFDIndex;
 virCommandPassListenFDs;
 virCommandRawStatus;
 virCommandRequireHandshake;

src/util/vircommand.c

@@ -1019,6 +1019,30 @@ virCommandPassListenFDs(virCommandPtr cmd)
     cmd->flags |= VIR_EXEC_LISTEN_FDS;
 }
 
+/*
+ * virCommandPassFDGetFDIndex:
+ * @cmd: pointer to virCommand
+ * @fd: FD to get index of
+ *
+ * Determine the index of the FD in the transfer set.
+ *
+ * Returns index >= 0 if @set contains @fd,
+ * -1 otherwise.
+ */
+int
+virCommandPassFDGetFDIndex(virCommandPtr cmd, int fd)
+{
+    size_t i = 0;
+
+    while (i < cmd->npassfd) {
+        if (cmd->passfd[i].fd == fd)
+            return i;
+        i++;
+    }
+
+    return -1;
+}
+
 /**
  * virCommandSetPidFile:
  * @cmd: the command to modify

src/util/vircommand.h

@@ -62,6 +62,9 @@ void virCommandPassFD(virCommandPtr cmd,
 
 void virCommandPassListenFDs(virCommandPtr cmd);
 
+int virCommandPassFDGetFDIndex(virCommandPtr cmd,
+                               int fd);
+
 void virCommandSetPidFile(virCommandPtr cmd,
                           const char *pidfile) ATTRIBUTE_NONNULL(2);