[Qemu-devel] [PATCH] virtio-bus: avoid breaking build when open DEBUG switch

[Qemu-devel] [PATCH] virtio-bus: avoid breaking build when open DEBUG switch

[arei.gonglei]

From: Gonglei <arei.gonglei@huawei.com>

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
---
 hw/virtio/virtio-bus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index eb77019..dfd2d8c 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -58,7 +58,7 @@ void virtio_bus_reset(VirtioBusState *bus)
 {
     VirtIODevice *vdev = virtio_bus_get_device(bus);
 
-    DPRINTF("%s: reset device.\n", qbus->name);
+    DPRINTF("%s: reset device.\n", BUS(bus)->name);
     if (vdev != NULL) {
         virtio_reset(vdev);
     }
-- 
1.7.12.4

Re: [Qemu-devel] [PATCH] virtio-bus: avoid breaking build when open DEBUG switch

[Stefan Hajnoczi]

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On Thu, Nov 13, 2014 at 10:39:32AM +0800, arei.gonglei@huawei.com wrote:
> From: Gonglei <arei.gonglei@huawei.com>
> 
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
>  hw/virtio/virtio-bus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [Qemu-devel] [PATCH] virtio-bus: avoid breaking build when open DEBUG switch

[Stefan Hajnoczi]

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On Thu, Nov 13, 2014 at 10:39:32AM +0800, arei.gonglei@huawei.com wrote:
> From: Gonglei <arei.gonglei@huawei.com>
> 
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
>  hw/virtio/virtio-bus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
> index eb77019..dfd2d8c 100644
> --- a/hw/virtio/virtio-bus.c
> +++ b/hw/virtio/virtio-bus.c
> @@ -58,7 +58,7 @@ void virtio_bus_reset(VirtioBusState *bus)
>  {
>      VirtIODevice *vdev = virtio_bus_get_device(bus);
>  
> -    DPRINTF("%s: reset device.\n", qbus->name);
> +    DPRINTF("%s: reset device.\n", BUS(bus)->name);

In general the problem with existing DPRINTF() macros is that they use
#ifdef.  This leads to bitrot, such as this instance.

A better approach is:

#define DEBUG_FOO 0
#define DPRINTF(...) \
do { \
    if (DEBUG_FOO) { \
        fprintf(stderr, ...); \
    } \
} while (0)

Now the compiler always checks the DPRINTF() code.

Trace events can be a good solution too.  If you like stderr output,
build QEMU with ./configure --enable-trace-backend=stderr and all
trace_*() calls are turned into fprintf(stderr).

The cool thing about trace events is that they are available in
production too.

Stefan

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Re: [Qemu-devel] [PATCH] virtio-bus: avoid breaking build when open DEBUG switch

[Gonglei]

On 2014/11/13 19:27, Stefan Hajnoczi wrote:

> On Thu, Nov 13, 2014 at 10:39:32AM +0800, arei.gonglei@huawei.com wrote:
>> From: Gonglei <arei.gonglei@huawei.com>
>>
>> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
>> ---
>>  hw/virtio/virtio-bus.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
>> index eb77019..dfd2d8c 100644
>> --- a/hw/virtio/virtio-bus.c
>> +++ b/hw/virtio/virtio-bus.c
>> @@ -58,7 +58,7 @@ void virtio_bus_reset(VirtioBusState *bus)
>>  {
>>      VirtIODevice *vdev = virtio_bus_get_device(bus);
>>  
>> -    DPRINTF("%s: reset device.\n", qbus->name);
>> +    DPRINTF("%s: reset device.\n", BUS(bus)->name);
> 
> In general the problem with existing DPRINTF() macros is that they use
> #ifdef.  This leads to bitrot, such as this instance.
> 

Yes.

> A better approach is:
> 
> #define DEBUG_FOO 0
> #define DPRINTF(...) \
> do { \
>     if (DEBUG_FOO) { \
>         fprintf(stderr, ...); \
>     } \
> } while (0)
> 
> Now the compiler always checks the DPRINTF() code.
> 
> Trace events can be a good solution too.  If you like stderr output,
> build QEMU with ./configure --enable-trace-backend=stderr and all
> trace_*() calls are turned into fprintf(stderr).
> 
> The cool thing about trace events is that they are available in
> production too.
> 

Hum, trace events is great! :)

Best regards,
-Gonglei

Re: [Qemu-devel] [Qemu-trivial] [PATCH] virtio-bus: avoid breaking build when open DEBUG switch

[Michael Tokarev]

Applied to -trivial as is, for now, since
the fixes are necessary anyway.  Good suggestion
by Stefan, to turn it into constant-depending
always-compilable code stands, but it is not
a show-stopper for the actual fix.

Thanks,

/mnt