Re: libdvdread: Can't seek to block 256

Tue Dec 09 2003, Felix Kurth wrote:
> 
> The shit happens in device.c  from libdvdcss-1.2.8
> on line 425
> static int libc_seek( dvdcss_t dvdcss, int i_blocks )
> i_blocks==256
> dvdcss seems valid.
> 
> it calls on line 435 
> i_seek = lseek( dvdcss->i_read_fd,
>  		                    (off_t)i_blocks * (off_t)DVDCSS_BLOCK_SIZE, SEEK_SET );
> where 
> dvdcss->i_read_fd == 3
> DVDCSS_BLOCK_SIZE=2048
> SEEK_SET==0
> this returns -1
> 
> in the strace i read 
> 
> _llseek(3, 524288, 0xbfffc4f0, SEEK_SET) -1 EINVAL (Invalid argument)
> 
> evaluating  "0xbfffc4f0" to decimal returns "-1073756944"
> (is this a valid value  ?)
> 
> evaluating 256*2048 returns "524288" or hex "80000"
> 
Ok so that is the same as the 'high' part of the _llseek call.
It should have been passed in the low word and the high should
have been zeroed.  Looks like a prototype and/or compiler bug.
Not 100% sure that the code is ok though.

> what happens in lseek ? Why comming from 80000 to -1073756944 ?
>  what can i do ? Compile glibc with -q and debug deeper ?
> 
Na...

Try and add the following to this function

  off_t pos = (off_t)i_blocks * (off_t)DVDCSS_BLOCK_SIZE;
and pass that to the lseek call.

You could try an print that also
fprintf(stderr, "off_t pos is %ll\n", pos);

> man _llseek
> says
> int  _llseek(unsigned int fd, unsigned long offset_high, unsigned long 
> offset_low, loff_t *result, unsigned int whence);
> EINVAL: whence is invalid.
> 
> but the call in the strace has only 4 parameters, no "whence" is set ?
> (my glibc ver is 2.3.2)
> 
Did you use a binary distrubution for libdvdcss?  If so are you sure
that was compiled agains the same version of glibc ?
If you used a binary package you could try and compile and install
libdvdcss from source.

> How can i make an executable link against a lib in an other then the
> default location ?
> I wont install a self-compiled glibc on my system since i dont want to break 
> it.
> 
That way lies ruin... we should be able to solve this some other way.

-- 
Håkan Hjort