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References: <001201c4b224$fcd68320$65cfe404@shawns>
            <20041013210029.GA88757@dan.emsphone.com>
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From: shawnwebb@softhome.net
To: Dan Nelson <dnelson@allantgroup.com>
Date: Wed, 13 Oct 2004 19:36:59 -0600
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cc: freebsd-hackers@freebsd.org
Subject: Re: malloc calls and ioctl calls to soundcard cause segfault
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Thanks for pointing that out. The OSS documentation didn't go into detail 
about what type of arg was needed for getospace, so I assumed int. 

Dan Nelson writes: 

> In the last episode (Oct 14), Shawn Webb said:
>> I've got to rewrite the source due to hard disk problems, so I'll just put
>> it in this email: 
>> 
>>     arg = FORMAT;
>>     if (ioctl(fd, SNDCTL_DSP_SETFMT, &arg) < 0)
>>     {
>>         perror("ioctl setfmt");
>>         exit(1);
>>     } 
>> 
>>     if (ioctl(fd, SNDCTL_DSP_GETOSPACE, &arg) < 0)
>>     {
>>         perror("ioctl getospace");
>>         exit(1);
>>     }
> 
> SNDCTL_DSP_GETOSPACE takes a pointer to an "audio_buf_info" type, so
> you actually asked it to write sizeof(audio_buf_info) bytes to the
> location of the "arg" variable, which is... (drumroll) 
> 
> on the stack :) 
> 
> Create another variable "audio_buf_info info;" above main, and change
> that call to "if (ioctl(fd, SNDCTL_DSP_GETOSPACE, &info) < 0)" and your
> program will run fine. 
> 
> -- 
> 	Dan Nelson
> 	dnelson@allantgroup.com
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