[libvirt] [PATCH] util: ensure safe{read, write, zero} return is checked

[Eric Blake]

Based on a warning from coverity.  The safe* functions
guarantee complete transactions on success, but don't guarantee
freedom from failure.

* src/util/util.h (saferead, safewrite, safezero): Add
ATTRIBUTE_RETURN_CHECK.
* src/remote/remote_driver.c (remoteIO, remoteIOEventLoop): Ignore
some failures.
(remoteIOReadBuffer): Adjust error messages on read failure.
* daemon/event.c (virEventHandleWakeup): Ignore read failure.
---

Coverity claimed that safewrite was checked 37 out of 46 times,
but only flagged one instance of a CHECKED_RETURN report,
against remote_driver.c.  I didn't spot the 9 unchecked calls
that coverity's numbers would imply.  Meanwhile, adding
the attribute ensures that we don't forget this in the future.

Please double-check if my use of ignore_value on some of the
previously unchecked calls makes sense, or if we need a more
invasive patch to deal with real failure.

 daemon/event.c             |    5 +++--
 src/remote/remote_driver.c |   13 +++++++++----
 src/util/util.h            |    9 ++++++---
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/daemon/event.c b/daemon/event.c
index 2218a3e..36e9dd3 100644
--- a/daemon/event.c
+++ b/daemon/event.c
@@ -1,8 +1,8 @@
 /*
  * event.c: event loop for monitoring file handles
  *
+ * Copyright (C) 2007, 2010 Red Hat, Inc.
  * Copyright (C) 2007 Daniel P. Berrange
- * Copyright (C) 2007 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
@@ -35,6 +35,7 @@
 #include "event.h"
 #include "memory.h"
 #include "util.h"
+#include "ignore-value.h"

 #define EVENT_DEBUG(fmt, ...) DEBUG(fmt, __VA_ARGS__)

@@ -630,7 +631,7 @@ static void virEventHandleWakeup(int watch ATTRIBUTE_UNUSED,
 {
     char c;
     virEventLock();
-    saferead(fd, &c, sizeof(c));
+    ignore_value (saferead(fd, &c, sizeof(c)));
     virEventUnlock();
 }

diff --git a/src/remote/remote_driver.c b/src/remote/remote_driver.c
index def4617..47d8c56 100644
--- a/src/remote/remote_driver.c
+++ b/src/remote/remote_driver.c
@@ -7809,7 +7809,9 @@ remoteIOReadBuffer(virConnectPtr conn,

                 char errout[1024] = "\0";
                 if (priv->errfd != -1) {
-                    saferead(priv->errfd, errout, sizeof(errout));
+                    if (saferead(priv->errfd, errout, sizeof(errout)) < 0) {
+                        strncpy (errout, _("unknown reason"), sizeof errout);
+                    }
                 }

                 virReportSystemError(errno,
@@ -7818,7 +7820,9 @@ remoteIOReadBuffer(virConnectPtr conn,
             } else {
                 char errout[1024] = "\0";
                 if (priv->errfd != -1) {
-                    saferead(priv->errfd, errout, sizeof(errout));
+                    if (saferead(priv->errfd, errout, sizeof(errout)) < 0) {
+                        strncpy (errout, _("unknown reason"), sizeof errout);
+                    }
                 }

                 errorf (in_open ? NULL : conn,
@@ -8431,7 +8435,8 @@ remoteIOEventLoop(virConnectPtr conn,

         if (fds[1].revents) {
             DEBUG0("Woken up from poll by other thread");
-            saferead(priv->wakeupReadFD, &ignore, sizeof(ignore));
+            ignore_value (saferead(priv->wakeupReadFD, &ignore,
+                                   sizeof(ignore)));
         }

         if (ret < 0) {
@@ -8575,7 +8580,7 @@ remoteIO(virConnectPtr conn,
             priv->waitDispatch = thiscall;

         /* Force other thread to wakup from poll */
-        safewrite(priv->wakeupSendFD, &ignore, sizeof(ignore));
+        ignore_value (safewrite(priv->wakeupSendFD, &ignore, sizeof(ignore)));

         DEBUG("Going to sleep %d %p %p", thiscall->proc_nr, priv->waitDispatch, thiscall);
         /* Go to sleep while other thread is working... */
diff --git a/src/util/util.h b/src/util/util.h
index cc05abe..34b77fa 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -2,6 +2,7 @@
 /*
  * utils.h: common, generic utility functions
  *
+ * Copyright (C) 2010 Red Hat, Inc.
  * Copyright (C) 2006, 2007 Binary Karma
  * Copyright (C) 2006 Shuveb Hussain
  *
@@ -31,9 +32,11 @@
 #include <sys/select.h>
 #include <sys/types.h>

-int saferead(int fd, void *buf, size_t count);
-ssize_t safewrite(int fd, const void *buf, size_t count);
-int safezero(int fd, int flags, off_t offset, off_t len);
+int saferead(int fd, void *buf, size_t count) ATTRIBUTE_RETURN_CHECK;
+ssize_t safewrite(int fd, const void *buf, size_t count)
+    ATTRIBUTE_RETURN_CHECK;
+int safezero(int fd, int flags, off_t offset, off_t len)
+    ATTRIBUTE_RETURN_CHECK;

 enum {
     VIR_EXEC_NONE   = 0,
-- 
1.6.6.1