item_in_dir() shell function does not handle missing directory

Binary package hint: os-prober

This concerns os-prober 1.44ubuntu1 in Ubuntu Natty.

When I invoke update-grub(8) in a certain chroot'ed Ubuntu installation, I see this:

Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.38-8-generic
Found initrd image: /boot/initrd.img-2.6.38-8-generic
Found memtest86+ image: /boot/memtest86+.bin
  No volume groups found
ls: cannot access /config: No such file or directory
ls: cannot access /config: No such file or directory
ls: cannot access /config: No such file or directory
ls: cannot access /config: No such file or directory
ls: cannot access /config: No such file or directory
ls: cannot access /config: No such file or directory
ls: cannot access /config: No such file or directory
done

I have a filesystem mounted on /config outside of the chroot. Because the system /proc directory is bind-mounted inside the chroot, /proc/mounts shows the /config mount, even though it is not accessible.

I traced the operation of update-grub(8) to see what was producing the ls(1) errors, leading me to to the item_in_dir() function in /usr/share/os-prober/common.sh. Adding the following line to it, in the appropriate place...

    [ -d "$2" ] || return 1

...makes the problem go away.