[DVDnav-discuss] [PATCH] handle duplicate language units and pgc's more gracefully

[John Stebbins]

On 11/04/2012 02:51 PM, Fabian Keil wrote:
> John Stebbins <stebbins at jetheaddev.com> wrote:
>
>> This patch never got accepted (probably because it's touches a lot and
>> made you nervous), but HandBrake has been applying this for 3 years now.
>>
>> Some discs have large numbers of repeated language units and pgc's that
>> cause extreme memory consumption and file i/o issues. scanning all the
>> titles on such discs is unusably slow. detect such repeats and ref-count
>> the data structures to avoid reading and storing duplicate info.
> A couple of days ago dvdbackup got killed after the system ran out of
> swap space (2 GB), I applied this patch and it solved the problem.
> Awesome.
>
> While I assumed that the changes from malloc() to calloc() might
> also make crashes due to bogus pgc field values less likely, the
> patch actually causes at least one crash that doesn't happen without
> it:
>
> Program terminated with signal 10, Bus error.
> #0  0x0000000802a2390a in dvdnav_describe_title_chapters (this=0x80cd03e00, title=17, times=0x7fffff8fa298, duration=0x7fffff8fa2a0)
>     at /usr/obj-ports/usr/ports/multimedia/libdvdnav/work/libdvdnav-4.2.0/src/searching.c:628
> 628	    if(ptt[i].pgn > pgc->nr_of_programs) {
> (gdb) p *pgc
> Cannot access memory at address 0xe000e000000a620
>
> Everyone's favourite function dvdnav_describe_title_chapters() strikes
> again ...
>
> I haven't tracked down the cause yet.
>
> Letting the dup_* functions always return -1 doesn't seem to affect the
> problem and neither does modifying find_dup_pgc() to compare the whole
> pgc instead of just the start_byte or removing the added return in
> ifoRead_VTS_PTT_SRPT().
>
> As far as I can tell the DVD doesn't actually have duplicated pgcs.
>
> Fabian
>
What disc does it crash on?  HandBrake does not use
dvdnav_describe_title_chapters(), so this is a code path we have not
tested well enough it sounds like.  dvdbackup uses this?