From damailings at mcbf.net  Thu Apr 24 22:42:22 2008
From: damailings at mcbf.net (David Mohr)
Date: Thu Apr 24 22:42:32 2008
Subject: [Libburn-cutters] Revival! And also question about burn_drive_scan
	with busy drives
Message-ID: <472d4b250804242042x73bf77abwb8d4e079daff2cd4@mail.gmail.com>

Hi,
so I'm working on xfburn, and I have been talking a lot to Mario
already. Thomas might remember me from some obscure bug reports ;-).

When the drive is mounted, and xfburn is started, then I can't get
access to the drive and burn_drive_scan returns 0 drives found. What
I'm missing is a way to enumerate drives even when they are currently
busy. I've looked through the API and I didn't see anything that would
get me that at the moment.

So I could get this list through i.e. HAL, but I'd rather keep my core
code libburn only. Is there a way that I could get that functionality
into libburn?

The reason is that in a GUI program I can't just bail out because the
drive is currently mounted. Rather the behavior that I want to get is
to list the drive, and try to automatically unmount it. I know the
unmounting is out of the scope of libburn, and I can deal with that
separately, but it would make things much cleaner if I could go
through libburn to maintain my main list of drives in the system.

Thanks,
~David
From scdbackup at gmx.net  Fri Apr 25 03:09:32 2008
From: scdbackup at gmx.net (Thomas Schmitt)
Date: Fri Apr 25 03:10:13 2008
Subject: [Libburn-cutters] Re: Revival! And also question about
	burn_drive_scan with busy drives
In-Reply-To: <472d4b250804242042x73bf77abwb8d4e079daff2cd4@mail.gmail.com>
References: <472d4b250804242042x73bf77abwb8d4e079daff2cd4@mail.gmail.com>
Message-ID: <101847718410002@212.46.126.165>

Hi,
 
> When the drive is mounted, and xfburn is started, then I can't get
> access to the drive and burn_drive_scan returns 0 drives found. What
> I'm missing is a way to enumerate drives even when they are currently
> busy. I've looked through the API and I didn't see anything that would
> get me that at the moment.
> ...
> So I could get this list through i.e. HAL, but I'd rather keep my core
> code libburn only. Is there a way that I could get that functionality
> into libburn?

That would be API call
  burn_preset_device_open(0, 0, 0);
but be warned that this might be a bad idea.

Normally libburn stays away from any drive that is
opened with O_EXCL flag. Afaik, mount does this
to indicate that it works on the drive.
libburn itself uses open(O_EXCL) to coordinate
with other instances of itself or with other
burn programs which use O_EXCL too. 

The problem with accessing busy drives is that
even the slightest glimpse might spoil an
ongoing burn run.
It's like quantum mechanics: you do not know
before you disturbed a potentially delicate state.


> The reason is that in a GUI program I can't just bail out because the
> drive is currently mounted. Rather the behavior that I want to get is
> to list the drive, and try to automatically unmount it.

Seems ok for the mount case but not ok for the case
of concurrently running burn programs.
If you touch a burning drive then the burn might fail
immediately.

With the case of a mounted drive i would advise to
set burn_preset_device_open(0, 0, 0) only for getting
an overview, to afterwards give up all found drives
by burn_drive_info_free() and to re-enable the
exclusive locking by
  burn_preset_device_open(1, 0, 0);
before doing a normal aquiration of drives.

This gives you the best chances not to collide
with other programs on a drive. It is still not
overly user-safe, i must say.


> So I could get this list through i.e. HAL,

Do you have experience with HAL ?
Do you know a way to tell HAL to stay away from
a particular drive for a while ?

For now, HAL is the biggest menace to libburn.
On my SuSE 10.2 i have to shoot the processes
  hald-addon-storage
which guard my drives. If i let them live, then
they grope my drives which spoils my burns.

I would like to send HAL a message when libburn
grabs a drive and another message when the drive
gets released. Inbetween it shall not touch my
drive in what way ever.

Any hint is welcome.


Have a nice day :)

Thomas