[FFmpeg-devel] [PATCH 1/2] dshow: fix return code when opening device

[Don Moir]

> On date Tuesday 2012-12-04 04:22:06 -0200, Ramiro Polla encoded:
>> Hi,
>>
>> I've sent this patch before, but I had forgotten why I had written it.
>> Thanks to Don Moir for pointing out why it was necessary.
>>
>> Ramiro
>
>> From d2d9631a110bbb28d5aa2082fe508df5739543ac Mon Sep 17 00:00:00 2001
>> From: Ramiro Polla <ramiro.polla at gmail.com>
>> Date: Tue, 4 Dec 2012 02:29:43 -0200
>> Subject: [PATCH 1/2] dshow: fix return code when opening device
>>
>> Successfully opening a device altered the ret variable, making the function
>> not cleanup properly and return an incorrect value for errors that happened
>> afterwards.
>> ---
>>  libavdevice/dshow.c |   18 ++++++++----------
>>  1 files changed, 8 insertions(+), 10 deletions(-)
>>
>> diff --git a/libavdevice/dshow.c b/libavdevice/dshow.c
>> index ea01b2a..18a4ee9 100644
>> --- a/libavdevice/dshow.c
>> +++ b/libavdevice/dshow.c
>> @@ -929,20 +929,18 @@ static int dshow_read_header(AVFormatContext *avctx)
>>      }
>>
>>      if (ctx->device_name[VideoDevice]) {
>> -        ret = dshow_open_device(avctx, devenum, VideoDevice);
>> -        if (ret < 0)
>> -            goto error;
>> -        ret = dshow_add_device(avctx, VideoDevice);
>> -        if (ret < 0)
>> +        if ((r = dshow_open_device(avctx, devenum, VideoDevice)) < 0 ||
>> +            (r = dshow_add_device(avctx, VideoDevice) < 0)) {
>> +            ret = r;
>>              goto error;
>> +        }
>
> Isn't this perfectly equivalent to the pre-existing code? The only
> difference is that in case of success it sets the ret value to the
> return code of dshow_open/add_device, which is finally returned (while
> the other failures, e.g. if (!ctx->mutex), don't change the default
> return value of 0, so won't cause a failure, is this intended?).

The problem with the pre-existing code is that ret has been set to a zero value indicating success. If it fails after the above 
chunk of code it just does a goto error with a successful return (ret) value. That patch has a ')'  wrong in 2 places though.

When a device it already open in another app and you try to open it in ffmpeg what would happen is all would succeed until you hit 
the IMediaControl_Run statement which would fail and return success to the calling function since the error ret value was over 
written with a success value.

I am doing some testing with this and more related to dshow so wait