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

[Fabian Keil]

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
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