"tar tfv /dev/cd0" speedup patch; Linux compatibility patches

[Tim Kientzle]

Juergen Lock wrote:
> On Sun, Feb 21, 2010 at 05:17:37PM -0800, Tim Kientzle wrote:
>>
>> Could you try the current version of read_open_filename from:
>>
>> http://libarchive.googlecode.com/svn/trunk/libarchive/archive_read_open_filename.c
>
> Small but important bug:
> 
> Index: archive_read_open_filename.c
> @@ -94,7 +94,7 @@ archive_read_open_filename(struct archiv
>  	struct read_file_data *mine;
>  	void *buffer;
>  	int fd;
> -	int is_disk_like;
> +	int is_disk_like = 0;

Ah.  Good catch!

  >  Btw...  the lseek + read combinations could also be replaced with
> pread(2), for the least amount of syscalls. :)

Unfortunately, pread() isn't as portable.  It's
an interesting idea, though; maybe I'll play with that.

>  (Especially since I
> noticed this version at least when ran on an optical disc with iso9660
> ends up doing lots of lseek()s towards the end without ever reading
> anything from the disc anymore...)

Fortunately, because there are no reads, those lseek()
requests are pretty cheap.  But you're right, it
wouldn't be hard to eliminate the unnecessary system
calls.

>  Patches are here: (made on stable/8, if they don't apply on head
> I'll have to make extra versions for that...)
> 	http://people.freebsd.org/~nox/linuxdisk-blk.patch [1]
> 	http://people.freebsd.org/~nox/lseek-seek_end.patch [2]

I'll let someone more familiar with the linuxolator code
comment on those.

>  And yes, with these patches the Linux bsdtar now also runs fast
> on FreeBSD. :)

Excellent!

Thanks so much for your help.  If you have any further
ideas (or patches ;-) for improving that libarchive
code, please let me know.

Cheers,

Tim