[Qemu-devel] [Fwd: qemu-0.11.1 / tap device bug]

[Victor Dorneanu <victor@dornea.nu>]

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Hi there!

I send you some bug report I've reported to NetBSD's mailing lists.

-- 
Victor Dorneanu


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Hello there!

I don't know if you can remember this thread [1]. Whenever I tried to
use some previously configured TAP device, I got a segmentation fault. I
thought it could some brilliant idea to have a look at the sources and
try to find out what's causing that error. After several gdb sessions,
it turned out qemu was accessing the wrong device.

-------------- File: net.c / Lines:1466-1470 --------------

    TFR(fd = open("/dev/tap", O_RDWR));

    if (fd < 0) {

        fprintf(stderr, "warning: could not open /dev/tap: no virtual network emulation\n");

        return -1;

    }

-----------------------------------------------------------------------

If you run qemu like this:

$ qemu -net tap,ifname=tap0 ...


why is "/dev/tap" being used as tap device?! It should be "/dev/tap0". I
have attached a patch which should do the work.
Any suggestions/improvements are appreciated.


Links:
[1] http://mail-index.netbsd.org/netbsd-users/2009/11/25/msg004957.html

-- 
Victor Dorneanu

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--- net.c.orig	2009-12-18 18:24:20.000000000 +0100
+++ net.c	2009-12-18 18:19:07.000000000 +0100
@@ -116,7 +116,7 @@
 #include "sysemu.h"
 #include "qemu-timer.h"
 #include "qemu-char.h"
-#include "audio/audio.h"
+#include "audio/qaudio.h"
 #include "qemu_socket.h"
 #include "qemu-log.h"
 
@@ -1461,11 +1461,27 @@
 {
     int fd;
     char *dev;
+    char tap_dev[1024];
     struct stat s;
 
-    TFR(fd = open("/dev/tap", O_RDWR));
+#if defined (__NetBSD__)
+    // Concatenate dev path (/dev/) and tap device name (e.g. tap0)
+    if (strlcpy(tap_dev, "/dev/", sizeof(tap_dev)) >= sizeof(tap_dev)) {
+        fprintf(stderr, "error: tap device name too long\n");
+        return -1;
+    }
+
+    if (strlcat(tap_dev, ifname, sizeof(tap_dev)) >= sizeof(tap_dev)) {
+        fprintf(stderr, "error: tap device name too long\n");
+        return -1;
+    }
+#else
+    tap_dev="/dev/tap";
+#endif
+    TFR(fd = open(tap_dev, O_RDWR));
+
     if (fd < 0) {
-        fprintf(stderr, "warning: could not open /dev/tap: no virtual network emulation\n");
+        fprintf(stderr, "warning: could not open %s: no virtual network emulation\n",tap_dev);
         return -1;
     }