util: add virCommandPassListenFDs() function

That sets a new flag, but that flag does mean the child will get
LISTEN_FDS and LISTEN_PID environment variables properly set and
passed FDs reordered so that it corresponds with LISTEN_FDS (they must
start right after STDERR_FILENO).

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

src/libvirt_private.syms

@@ -1146,6 +1146,7 @@ virCommandNewArgList;
 virCommandNewArgs;
 virCommandNonblockingFDs;
 virCommandPassFD;
+virCommandPassListenFDs;
 virCommandRawStatus;
 virCommandRequireHandshake;
 virCommandRun;

src/util/vircommand.c

@@ -66,6 +66,7 @@ enum {
     VIR_EXEC_CLEAR_CAPS = (1 << 2),
     VIR_EXEC_RUN_SYNC   = (1 << 3),
     VIR_EXEC_ASYNC_IO   = (1 << 4),
+    VIR_EXEC_LISTEN_FDS = (1 << 5),
 };
 
 typedef struct _virCommandFD virCommandFD;
@@ -200,6 +201,78 @@ virCommandFDSet(virCommandPtr cmd,
     return 0;
 }
 
+static void
+virCommandReorderFDs(virCommandPtr cmd)
+{
+    int maxfd = 0;
+    int openmax = 0;
+    size_t i = 0;
+
+    if (!cmd || cmd->has_error || !cmd->npassfd)
+        return;
+
+    for (i = 0; i < cmd->npassfd; i++)
+        maxfd = MAX(cmd->passfd[i].fd, maxfd);
+
+    openmax = sysconf(_SC_OPEN_MAX);
+    if (openmax < 0 ||
+        maxfd + cmd->npassfd > openmax)
+        goto error;
+
+    /*
+     * Simple two-pass sort, nothing fancy.  This is not designed for
+     * anything else than passing around 2 FDs into the child.
+     *
+     * So first dup2() them somewhere else.
+     */
+    for (i = 0; i < cmd->npassfd; i++) {
+        int newfd = maxfd + i + 1;
+        int oldfd = cmd->passfd[i].fd;
+        if (dup2(oldfd, newfd) != newfd) {
+            virReportSystemError(errno,
+                                 _("Cannot dup2() fd %d before "
+                                   "passing it to the child"),
+                                 oldfd);
+            goto error;
+        }
+        VIR_FORCE_CLOSE(cmd->passfd[i].fd);
+    }
+
+    VIR_DEBUG("First reorder pass done");
+
+    /*
+     * And then dup2() them in orderly manner.
+     */
+    for (i = 0; i < cmd->npassfd; i++) {
+        int newfd = STDERR_FILENO + i + 1;
+        int oldfd = maxfd + i + 1;
+        if (dup2(oldfd, newfd) != newfd) {
+            virReportSystemError(errno,
+                                 _("Cannot dup2() fd %d before "
+                                   "passing it to the child"),
+                                 oldfd);
+            goto error;
+        }
+        if (virSetInherit(newfd, true) < 0) {
+            virReportSystemError(errno,
+                                 _("Cannot set O_CLOEXEC on fd %d before "
+                                   "passing it to the child"),
+                                 newfd);
+            goto error;
+        }
+        VIR_FORCE_CLOSE(oldfd);
+        cmd->passfd[i].fd = newfd;
+    }
+
+    VIR_DEBUG("Second reorder pass done");
+
+    return;
+
+ error:
+    cmd->has_error = -1;
+    return;
+}
+
 #ifndef WIN32
 
 /**
@@ -678,6 +751,15 @@ virExec(virCommandPtr cmd)
         goto fork_error;
     }
 
+    if (cmd->flags & VIR_EXEC_LISTEN_FDS) {
+        virCommandReorderFDs(cmd);
+        virCommandAddEnvFormat(cmd, "LISTEN_PID=%u", getpid());
+        virCommandAddEnvFormat(cmd, "LISTEN_FDS=%zu", cmd->npassfd);
+
+        if (cmd->has_error)
+            goto fork_error;
+    }
+
     /* Close logging again to ensure no FDs leak to child */
     virLogReset();
 
@@ -918,6 +1000,23 @@ virCommandPassFD(virCommandPtr cmd, int fd, unsigned int flags)
     }
 }
 
+/**
+ * virCommandPassListenFDs:
+ * @cmd: the command to modify
+ *
+ * Pass LISTEN_FDS and LISTEN_PID environment variables into the
+ * child.  LISTEN_PID has the value of the child's PID and LISTEN_FDS
+ * is a number of passed file descriptors starting from 3.
+ */
+void
+virCommandPassListenFDs(virCommandPtr cmd)
+{
+    if (!cmd || cmd->has_error)
+        return;
+
+    cmd->flags |= VIR_EXEC_LISTEN_FDS;
+}
+
 /**
  * virCommandSetPidFile:
  * @cmd: the command to modify

src/util/vircommand.h

@@ -1,7 +1,7 @@
 /*
  * vircommand.h: Child command execution
  *
- * Copyright (C) 2010-2013 Red Hat, Inc.
+ * Copyright (C) 2010-2014 Red Hat, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -60,6 +60,8 @@ void virCommandPassFD(virCommandPtr cmd,
                       int fd,
                       unsigned int flags);
 
+void virCommandPassListenFDs(virCommandPtr cmd);
+
 void virCommandSetPidFile(virCommandPtr cmd,
                           const char *pidfile) ATTRIBUTE_NONNULL(2);