On Sun, Jun 10, 2007 at 11:59:26AM -0700, H. Peter Anvin wrote:
> losetup provides an -f option to discover an unused loop device. As
> implemented, it is racy.
>
> The problem is that -f prints the loop device to stdout only when used
> standalone. This means a script has to do:
>
> lodev=`losetup -f`
> losetup $lodev $filename
>
> ... which is racy if another script may be running. The syntax:
Yes, this method is useless.
>
> lodev=`losetup -f $filename`
>
> ... doesn't work, because although it will set up the loop device for
> you (and it better do it atomically!), it never prints out the selected
> loop device for the script to use.
I use in util-linux-ng regression tests something like:
losetup -f "$IMAGE"
DEV=$( losetup -a | gawk 'BEGIN {FS=":"} /'$IMAGE'/ { print $1 }' )
(Note, old versions don't support the '-a' option. The '-a' means
list all used loop devices.)
We can print out the selected loop device name, but this change is
not backwardly compatible (it means scripts without "> /dev/null"
will be print the name of device to stdout, or log file, ...). The
other possibility is add a new option ('-p' when you need a device
name):
$lodev=`losetup -f -p filename.img`
Comments?
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
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