[libvirt] [PATCH] don't ignore write failure [was PATCH: 10/25: ...

[Jim Meyering]

"Daniel P. Berrange" <berrange at redhat.com> wrote:

> The strerror() method is not guarenteed to be re-entrant, which is
...

> @@ -759,8 +762,8 @@ static int networkStartNetworkDaemon(vir
>
>      if (network->def->forwardType != VIR_NETWORK_FORWARD_NONE &&
>          !networkEnableIpForwarding()) {
> -        networkReportError(conn, NULL, NULL, VIR_ERR_INTERNAL_ERROR,
> -                         _("failed to enable IP forwarding : %s"), strerror(err));
> +        virReportSystemError(conn, errno, "%s",
> +                             _("failed to enable IP forwarding"));
>          goto err_delbr2;
>      }
>

Looking at this chunk and the s/err/errno/ change (that's a bug fix),
I spotted another small bug:

Any write error in networkEnableIpForwarding was ignored,
I added a check for failed close, too, just in case.

Jim

>From b4abd36014b56cdb33a91ab336eff6450a5d3c8a Mon Sep 17 00:00:00 2001
From: Jim Meyering <meyering at redhat.com>
Date: Mon, 19 Jan 2009 10:11:15 +0100
Subject: [PATCH] don't ignore write failure

* src/network_driver.c (networkEnableIpForwarding): This function
would always return 1 (success).  Now it returns 0 upon write or
close failure, being careful to preserve any errno from a write failure.
Add comments.
---
 src/network_driver.c |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/network_driver.c b/src/network_driver.c
index 695acfb..51cfbbd 100644
--- a/src/network_driver.c
+++ b/src/network_driver.c
@@ -1,7 +1,7 @@
 /*
  * driver.c: core driver methods for managing qemu guests
  *
- * Copyright (C) 2006, 2007, 2008 Red Hat, Inc.
+ * Copyright (C) 2006-2009 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -774,20 +774,29 @@ networkRemoveIptablesRules(struct network_driver *driver,
     iptablesSaveRules(driver->iptables);
 }

+/* Enable IP Forwarding.
+   Return 0 for success, nonzero for failure.
+   Be careful to preserve any errno value upon failure. */
 static int
 networkEnableIpForwarding(void)
 {
 #define PROC_IP_FORWARD "/proc/sys/net/ipv4/ip_forward"

-    int fd, ret;
+    int fd;

     if ((fd = open(PROC_IP_FORWARD, O_WRONLY|O_TRUNC)) == -1)
         return 0;

-    if (safewrite(fd, "1\n", 2) < 0)
-        ret = 0;
+    if (safewrite(fd, "1\n", 2) < 0) {
+        int saved_errno = errno;
+        close (fd);
+        errno = saved_errno;
+        return 0;
+    }

-    close (fd);
+    /* Use errno from failed close only if there was no write error.  */
+    if (close (fd) != 0)
+        return 0;

     return 1;

@@ -1429,4 +1438,3 @@ int networkRegister(void) {
     virRegisterStateDriver(&networkStateDriver);
     return 0;
 }
-
--
1.6.1.258.g7ff14