[Pkg-uml-devel] Patch: enables to run rootstrap in the background

[Mattia Dongili]

On Sat, Nov 18, 2006 at 05:51:06PM +0200, shaulka at 012.net.il wrote:
>   Some words of explanation follow.
> 
> --- rootstrap.orig   2006-11-18 03:53:54.000000000 +0200
> +++ rootstrap        2006-11-18 15:10:00.000000000 +0200
> @@ -92,11 +92,22 @@
> 
>  umlargs.extend(umlargs_extra)
> 
> +if sys.stdin.isatty()  \
> +       and  \
> +   os.tcgetpgrp(sys.stdin.fileno()) != os.getpgrp():
> +   (block_on_read,not_to_be_written_to) = os.pipe()
> +   os.dup2(block_on_read, sys.stdin.fileno())
> +if sys.stdout.isatty()  \
> +       and  \
> +   os.tcgetpgrp(sys.stdout.fileno()) != os.getpgrp():
> +   sink = open('/dev/null','w')
> +   os.dup2(sink.fileno(), sys.stdout.fileno())
> +
>  umlargs.extend(['con0=fd:0,fd:1',
>                  'con=pts',
> -               'root=/dev/root',
> -               'rootflags=/',
> -               'rootfstype=hostfs',
> +                'root=/dev/root',
> +                'rootflags=/',
> +                'rootfstype=hostfs',
>                  'ubd1=' + imagefile,
>                  'init=/usr/lib/rootstrap/builder',
>                  'devfs=nomount',
> 
>   Explanation:
>    =========
> 
>   Note that rootstrap already duplicats the log file to stdout
> when the -o command line switch is invoked.
> 
>     if sys.std{in,out}.isatty()
> 
> insures us that std{in,out} uses the terminal, which is the opposite of
> being redirected (to a file or a pipe).
> 
>        os.tcgetpgrp(sys.std{in,out}.fileno()) != os.getpgrp()
> 
> tell us that rootstrap is running in the background.
> 
>   Those two idioms are my python equivalent of the C lines
> shown at http://www.ugcs.caltech.edu/manuals/libs/glibc-2.3.2/libc_581.html
> 
>      (block_on_read,not_to_be_written_to) = os.pipe()
> 
> will make the file descriptor block_on_read blocks on read
> while the descriptor not_to_be_written_to will not be closed and
> not be written to.
>   block_on_read + sink from the stdout duplication are assumed to
> be compatible with
> 
>     # Nothing - device=null
> 
>         This allows the device to be opened, in contrast to 'none', but reads
>         will block, and writes will succeed and the data will be thrown out.
> 
> from http://user-mode-linux.sourceforge.net/input.html.

hmmm, I was sure I tried something similar when I answered to your other
mail. Thanks for the suggestions.
Anyway, since uml already has some way of avoiding the tty usage why not
simply use "con=null con0=null" when rootstrap is not controlling the
terminal?

-- 
mattia
:wq!