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



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


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