Possible solution for the alsa-oss fopen problem.

Possible solution for the alsa-oss fopen problem.

[James Courtier-Dutton]

I have found out that the artsdsp /dev/oss redirector supports fopen and 
friends.
I looked at the artsdsp, (find it inside arts-1.2.2.tar.bz2)
It uses a function called fopencookie()

Extract from /arts-1.2.2/artsc/stdioemu.c below.

Would this be useable in the alsa-oss redirector?

Cheers
James



static FILE *fake_fopen(const char *path, const char *mode)
{
         cookie_io_functions_t fns = { fdc_read, fdc_write, fdc_seek, 
fdc_clean };
         struct fd_cookie *fdc =
                 (struct fd_cookie *)malloc(sizeof(struct fd_cookie));
         const char *mptr;
         int open_mode = 0;
         FILE *result = 0;

         for(mptr = mode; *mptr; mptr++)
         {
                 if(*mptr == 'r') open_mode |= 1; /* 1 = read */
                 if(*mptr == 'w') open_mode |= 2; /* 2 = write */
                 if(*mptr == '+') open_mode |= 3; /* 3 = readwrite */
                 if(*mptr == 'a') open_mode |= 2; /* append -> write */
         }
         if(open_mode == 1) fdc->fd = open(path,O_RDONLY,0666);
         if(open_mode == 2) fdc->fd = open(path,O_WRONLY,0666);
         if(open_mode == 3) fdc->fd = open(path,O_RDWR,0666);

         if(open_mode && fdc->fd > 0)
         {
                 result = fopencookie (fdc,"w", fns);
                 result->_fileno = fdc->fd;              /* ugly patchy 
slimy kludgy hack */
         }
         return result;
}


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Re: Possible solution for the alsa-oss fopen problem.

[Jaroslav Kysela]

On Wed, 9 Jun 2004, James Courtier-Dutton wrote:

> I have found out that the artsdsp /dev/oss redirector supports fopen and
> friends. I looked at the artsdsp, (find it inside arts-1.2.2.tar.bz2) It
> uses a function called fopencookie()

Does it work for sox and teamspeak?

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs


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Re: Possible solution for the alsa-oss fopen problem.

[James Courtier-Dutton]

Jaroslav Kysela wrote:
> On Wed, 9 Jun 2004, James Courtier-Dutton wrote:
> 
> 
>>I have found out that the artsdsp /dev/oss redirector supports fopen and
>>friends. I looked at the artsdsp, (find it inside arts-1.2.2.tar.bz2) It
>>uses a function called fopencookie()
> 
> 
> Does it work for sox and teamspeak?
> 
> 						Jaroslav
> 

I don't use KDE, so I can't really test it.
I just heard someone say on irc "It works on artsdsp, but not aoss"
I can't remember which app "It" was.

Has anyone created a test app that uses fopen and friends so that 
testing these features would be easier?

Cheers
James


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Re: Possible solution for the alsa-oss fopen problem.

[Florian Schmidt]

On Wed, 09 Jun 2004 12:10:45 +0100
James Courtier-Dutton <James@superbug.demon.co.uk> wrote:

> I have found out that the artsdsp /dev/oss redirector supports fopen and 
> friends.
> I looked at the artsdsp, (find it inside arts-1.2.2.tar.bz2)
> It uses a function called fopencookie()
> 
> Extract from /arts-1.2.2/artsc/stdioemu.c below.
> 
> Would this be useable in the alsa-oss redirector?

This fopencookie seems to be a libc thing to implement custom streams.. See

http://wwwwbs.cs.tu-berlin.de/user-taipan/kraxel/gnuinfo/libc/Streams_and_Cookies.html

Might be exctly the thing which is needed to intercept fopen() and friends AND handle the intercepted calls gracefully..

I have a question though: If this works for alsa-oss, then the libc problem with the internal symbols of open() and friends is solved. But i wonder if there are any other libs which are as "evil" in this regard as libc is. The basic problem persists: If a lib uses internal symbols for open() and friends and an app uses that lib to access /dev/dsp, etc., then we're screwed again..

On the other hand: How many libs besides libc do stuff like this? And how many apps use such a lib? I would guess: very very few.. If this is the case, i suppose it will work well (tm)

Florian Schmidt

-- 
Palimm Palimm!



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Re: Possible solution for the alsa-oss fopen problem.

[James Courtier-Dutton]

Florian Schmidt wrote:
> On Wed, 09 Jun 2004 12:10:45 +0100
> James Courtier-Dutton <James@superbug.demon.co.uk> wrote:
> 
> 
>>I have found out that the artsdsp /dev/oss redirector supports fopen and 
>>friends.
>>I looked at the artsdsp, (find it inside arts-1.2.2.tar.bz2)
>>It uses a function called fopencookie()
>>
>>Extract from /arts-1.2.2/artsc/stdioemu.c below.
>>
>>Would this be useable in the alsa-oss redirector?
> 
> 
> This fopencookie seems to be a libc thing to implement custom streams.. See
> 
> http://wwwwbs.cs.tu-berlin.de/user-taipan/kraxel/gnuinfo/libc/Streams_and_Cookies.html
> 
> Might be exctly the thing which is needed to intercept fopen() and friends AND handle the intercepted calls gracefully..
> 
> I have a question though: If this works for alsa-oss, then the libc problem with the internal symbols of open() and friends is solved. But i wonder if there are any other libs which are as "evil" in this regard as libc is. The basic problem persists: If a lib uses internal symbols for open() and friends and an app uses that lib to access /dev/dsp, etc., then we're screwed again..
> 
> On the other hand: How many libs besides libc do stuff like this? And how many apps use such a lib? I would guess: very very few.. If this is the case, i suppose it will work well (tm)
> 
> Florian Schmidt
> 

Does anyone have a small test app that uses fopen and friends, so that I 
could test them if I add fopencookie() to aoss.

Hopefully, the test app should use the fopen and friends calls in the 
same way that know "problem" apps use.

If there is not a test app out there, can someone please tell me more 
details about the problem, so that I could build a test app myself.

I need to know which fcalls lead to a failure, so that if I get those 
fcalls working, these "problem" apps will be guaranteed to work.

Cheers
James



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