emulate an end-of-media

[Martin Laabs]

Hi,

On Mon, 25 Feb 2008 20:34:31 +0100,  wrote:

> You might want to play with the -P option to dump. Your above could be
> written as:
>
> dump -aL0 -P 'compress -c' /MYFILESYSTEM | cdrecord dev=... -

Unfornunately this does not work as you expect. Dump just takes
its data an pass it to the script specified to -P.
It does not grab the output of the script to count the data after-
wards. This means the -a option does not work at all (because a
pipe has no EOM-Signal) and the -B option will limit the input
data only:

$ dump -0 -B 100 -P 'dd' /dev/md4 > /dev/null
   DUMP: Date of this level 0 dump: Mon Feb 25 21:11:40 2008
   DUMP: Date of last level 0 dump: the epoch
   DUMP: Dumping /dev/md4 to child pipeline process
   DUMP: mapping (Pass I) [regular files]
   DUMP: mapping (Pass II) [directories]
   DUMP: estimated 30022 tape blocks on 291.38 tape(s).
   DUMP: dumping (Pass III) [directories]
   DUMP: dumping (Pass IV) [regular files]
200+0 records in
200+0 records out
102400 bytes transferred in 0.031908 secs (3209223 bytes/sec)
   DUMP: Closing child pipeline process
   DUMP: Change Volumes: Mount volume #2
   DUMP: Is the new volume mounted and ready to go?: ("yes" or "no")

In contrast with:

$ dump -0 -B 100 -P 'compress -c' /dev/md4 | dd > /dev/null
   DUMP: Date of this level 0 dump: Mon Feb 25 21:12:23 2008
   DUMP: Date of last level 0 dump: the epoch
   DUMP: Dumping /dev/md4 to child pipeline process
   DUMP: mapping (Pass I) [regular files]
   DUMP: mapping (Pass II) [directories]
   DUMP: estimated 30022 tape blocks on 291.38 tape(s).
   DUMP: dumping (Pass III) [directories]
   DUMP: dumping (Pass IV) [regular files]
   DUMP: Closing child pipeline process
   DUMP: Change Volumes: Mount volume #2
   DUMP: Is the new volume mounted and ready to go?: ("yes" or "no") ^C
59+1 records in
59+0 records out
30208 bytes transferred in 6.315456 secs (4783 bytes/sec)

> Assuming that compress -c & cdrecord play nice (which your magic
> device solution also requires)

My solution can just close the pipe at the one "end" of the magic
device which would be realy simple to implement in a script.
Of cause cdrecord will indeet close the pipe when the media is full. But
I think the media will not be usable since there is i.e. just no
more space for finalisation of the dvd.
But this is not a big probleme since I can use my "count compressed
data and close stdin after is reaches limit x"-script.

> Well, if -B worked on compressed output, then  you could split it up
> on volumes, which wouldn't be quite so bad. So add making -P and -B
> play nice  together (again, they don't seem to as of 6.2) as a
> possible solution.

Yes - this would be the best solution at all. But as I wrote - the
-B option only counts the data thats thrown out to stdout from dump
and doesn't fetch stout again.
Changing this behaviour of dump would break the backward compati-
bility. (However - I could introduce a new Option i.e. -C for compress :-)
But I worrie about updates with such a modified dump because I
would have to patch the original dump every time after I'd
updated my system.
How hard is it to get those a change into the CORE-Tree when coded
and tested well?

Thank you,
  Martin L.