[Qemu-devel] [PATCH v2 06/15] tap: Improve -netdev/netdev_add/-net/... bridge error reporting

[Markus Armbruster <armbru@redhat.com>]

When -netdev bridge fails, it first reports a specific error, then a
generic one, like this:

    $ qemu-system-x86_64 -netdev bridge,id=foo
    failed to launch bridge helper
    qemu-system-x86_64: -netdev bridge,id=foo: Device 'bridge' could not be initialized

The first message goes to stderr.  Wrong for HMP, because errors need
to go to the monitor there.

The second message goes to stderr for -netdev, to the monitor for HMP
netdev_add, and becomes the error reply for QMP netdev_add.

Convert net_bridge_run_helper() to Error, and propagate its errors
through net_init_bridge().  This ensures the error gets reported where
the user is, and suppresses the unwanted second message.

While there, improve the error messages a bit.

The above example becomes:

    $ qemu-system-x86_64 -netdev bridge,id=foo
    qemu-system-x86_64: -netdev bridge,id=foo: bridge helper failed

net_init_tap() also uses net_bridge_run_helper().  Propagate its
errors there as well.  Improves reporting these errors with -netdev
tap & friends.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 net/tap.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index adb1022..23c81fa 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -437,7 +437,8 @@ static int recv_fd(int c)
     return len;
 }
 
-static int net_bridge_run_helper(const char *helper, const char *bridge)
+static int net_bridge_run_helper(const char *helper, const char *bridge,
+                                 Error **errp)
 {
     sigset_t oldmask, mask;
     int pid, status;
@@ -450,11 +451,16 @@ static int net_bridge_run_helper(const char *helper, const char *bridge)
     sigprocmask(SIG_BLOCK, &mask, &oldmask);
 
     if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
+        error_setg_errno(errp, errno, "socketpair() failed");
         return -1;
     }
 
     /* try to launch bridge helper */
     pid = fork();
+    if (pid < 0) {
+        error_setg_errno(errp, errno, "Can't fork bridge helper");
+        return -1;
+    }
     if (pid == 0) {
         int open_max = sysconf(_SC_OPEN_MAX), i;
         char fd_buf[6+10];
@@ -502,14 +508,16 @@ static int net_bridge_run_helper(const char *helper, const char *bridge)
         }
         _exit(1);
 
-    } else if (pid > 0) {
+    } else {
         int fd;
+        int saved_errno;
 
         close(sv[1]);
 
         do {
             fd = recv_fd(sv[0]);
         } while (fd == -1 && errno == EINTR);
+        saved_errno = errno;
 
         close(sv[0]);
 
@@ -518,22 +526,21 @@ static int net_bridge_run_helper(const char *helper, const char *bridge)
         }
         sigprocmask(SIG_SETMASK, &oldmask, NULL);
         if (fd < 0) {
-            fprintf(stderr, "failed to recv file descriptor\n");
+            error_setg_errno(errp, saved_errno,
+                             "failed to recv file descriptor");
             return -1;
         }
-
-        if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
-            return fd;
+        if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+            error_setg(errp, "bridge helper failed");
+            return -1;
         }
+        return fd;
     }
-    fprintf(stderr, "failed to launch bridge helper\n");
-    return -1;
 }
 
 int net_init_bridge(const NetClientOptions *opts, const char *name,
                     NetClientState *peer, Error **errp)
 {
-    /* FIXME error_setg(errp, ...) on failure */
     const NetdevBridgeOptions *bridge;
     const char *helper, *br;
     TAPState *s;
@@ -545,7 +552,7 @@ int net_init_bridge(const NetClientOptions *opts, const char *name,
     helper = bridge->has_helper ? bridge->helper : DEFAULT_BRIDGE_HELPER;
     br     = bridge->has_br     ? bridge->br     : DEFAULT_BRIDGE_INTERFACE;
 
-    fd = net_bridge_run_helper(helper, br);
+    fd = net_bridge_run_helper(helper, br, errp);
     if (fd == -1) {
         return -1;
     }
@@ -792,7 +799,8 @@ int net_init_tap(const NetClientOptions *opts, const char *name,
             return -1;
         }
 
-        fd = net_bridge_run_helper(tap->helper, DEFAULT_BRIDGE_INTERFACE);
+        fd = net_bridge_run_helper(tap->helper, DEFAULT_BRIDGE_INTERFACE,
+                                   errp);
         if (fd == -1) {
             return -1;
         }
-- 
1.9.3