[Qemu-devel] Re: [PATCH] net: provide a friendly message when a user passes a bad -net tap, fd=X

["Daniel P. Berrange" <berrange@redhat.com>]

On Fri, Oct 08, 2010 at 05:04:56PM -0500, Anthony Liguori wrote:
> A lot of people copy libvirt's command line from ps -ef and then wonder why the
> VM isn't working correctly.  Let's be kind and tell them what they should do
> instead.
> 
> Without this patch, if you run with an invalid -net tap,fd=X, the guest still
> runs and we poll 100% on a bad file descriptor.  With this patch, you get:
> 
>  qemu: -net tap,fd=42: invalid fd= for tap network device.  If you're copying
>  from libvirt, use `virsh dom2xml-to-native' instead
>  qemu: -net tap,fd=42: Device 'tap' could not be initialized
> 
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> 
> diff --git a/hw/usb-uhci.c b/hw/usb-uhci.c
> index 1d83400..5f9f749 100644
> --- a/hw/usb-uhci.c
> +++ b/hw/usb-uhci.c
> @@ -64,7 +64,7 @@
>  #define UHCI_PORT_CSC   (1 << 1)
>  #define UHCI_PORT_CCS   (1 << 0)
>  
> -#define FRAME_TIMER_FREQ 1000
> +#define FRAME_TIMER_FREQ 500
>  
>  #define FRAME_MAX_LOOPS  100
>  
> @@ -1054,7 +1054,7 @@ static void uhci_frame_timer(void *opaque)
>      UHCIState *s = opaque;
>  
>      /* prepare the timer for the next frame */
> -    s->expire_time += (get_ticks_per_sec() / FRAME_TIMER_FREQ);
> +    s->expire_time = qemu_get_clock(vm_clock) + (get_ticks_per_sec() / FRAME_TIMER_FREQ);
>  
>      if (!(s->cmd & UHCI_CMD_RS)) {
>          /* Full stop */
> diff --git a/net/tap.c b/net/tap.c
> index 0147dab..45b1fb6 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -405,6 +405,8 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>      int fd, vnet_hdr = 0;
>  
>      if (qemu_opt_get(opts, "fd")) {
> +        int flags;
> +
>          if (qemu_opt_get(opts, "ifname") ||
>              qemu_opt_get(opts, "script") ||
>              qemu_opt_get(opts, "downscript") ||
> @@ -418,6 +420,11 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>              return -1;
>          }
>  
> +        if (fcntl(fd, F_GETFL, &flags) == -1) {
> +            error_report("invalid fd= for tap network device.  If you're copying from libvirt, use `virsh dom2xml-to-native' instead");

It is just 'domxml-to-native' - no '2' in there.

Should it check for EBADF explicitly ? I guess this is the only errno that
can really happen here, but I always prefer strict checks myself.


Regards,
Daniel
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