[libvirt] [PATCHv2] command: avoid fd leak on failure

[Eric Blake]

On 07/14/2011 11:04 AM, Eric Blake wrote:
> virCommandTransferFD promises that the fd is no longer owned by
> the caller.  Normally, we want the fd to remain open until the
> child runs, but in error situations, we must close it earlier.
>
> To avoid any risks of double-close due to misunderstanding about
> this interface, change it to take a pointer which gets set to
> -1 in the caller to record that the transfer was successful.
>
> @@ -2109,8 +2115,8 @@ void virCommandRequireHandshake(virCommandPtr cmd)
>
>       VIR_DEBUG("Transfer handshake wait=%d notify=%d",
>                 cmd->handshakeWait[1], cmd->handshakeNotify[0]);
> -    virCommandTransferFD(cmd, cmd->handshakeWait[1]);
> -    virCommandTransferFD(cmd, cmd->handshakeNotify[0]);
> +    virCommandTransferFD(cmd,&cmd->handshakeWait[1]);
> +    virCommandTransferFD(cmd,&cmd->handshakeNotify[0]);

Unfortunately, resetting the caller's fd to -1 breaks handshake; here, 
cmd->handshakeWait[1] need to be closed in the parent, but not set to -1 
until after the child has been forked (setting to -1 here was too soon). 
  Squash this in:

diff --git i/src/util/command.c w/src/util/command.c
index 25494cf..3fda2cd 100644
--- i/src/util/command.c
+++ w/src/util/command.c
@@ -2292,6 +2292,8 @@ virCommandAbort(virCommandPtr cmd ATTRIBUTE_UNUSED)
   */
  void virCommandRequireHandshake(virCommandPtr cmd)
  {
+    int tmp;
+
      if (!cmd || cmd->has_error)
          return;

@@ -2314,8 +2316,12 @@ void virCommandRequireHandshake(virCommandPtr cmd)

      VIR_DEBUG("Transfer handshake wait=%d notify=%d",
                cmd->handshakeWait[1], cmd->handshakeNotify[0]);
-    virCommandTransferFD(cmd, &cmd->handshakeWait[1]);
-    virCommandTransferFD(cmd, &cmd->handshakeNotify[0]);
+    /* Transfer the fds now, but don't change the handshake arrays,
+     * because the child must see what fd it inherited.  */
+    tmp = cmd->handshakeWait[1];
+    virCommandTransferFD(cmd, &tmp);
+    tmp = cmd->handshakeNotify[0];
+    virCommandTransferFD(cmd, &tmp);
      cmd->handshake = true;
  }



-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org