How to find out if my Device's Kernel has Loop Device Support

Question

I would assume most all of you know why I am asking this, but for those who don't, Loop Device Support of a Kernel on an Android device is utilized to mount a Linux Distro IMG file (Ubuntu or Debian, & a couple others) to run the linux img in a Chrooted environment to run side by side next to your Android System.

So there is tons of information on what Loop Device Support is (if you need a good explanation see Wikipedia's article.), and why you need it, but there is a great lack of explaination as to how you find out if your device supports it. The most information relating to it is that "most roms support it"...

So down to the issue, how would one discover if my device currently supports it? Is there some script I can look at or something in the kernel I can view to find out if my device supports it?

Answer 1

You can verify by checking /proc/config.gz and search through it looking for the configure option - CONFIG_BLK_DEV_LOOP=y.

To do that you need to do it this way:

cp /proc/config.gz /sdcard/kernel_config.gz

and

adb pull /sdcard/kernel_config.gz

Unzip the kernel_config.gz and open it up in a notepad or text editor and search it.

If its either # CONFIG_BLK_DEV_LOOP is not set or CONFIG_BLK_DEV_LOOP=n all bets are off.

Answer 2

You can use the following command at the terminal:

export | grep LOOP_MOUNTPOINT

If there is a LOOP_MOUNPOINT, probably you can mount loop devices.

UPDATED

HOW TO TEST?

Download a freedos image (http://www.freedos.org/) 40MB ISO.

Make a loop device association:

losetup /dev/block/loop4 fd11src.iso 

Mount a iso device

mkdir freedos_img
mount -t iso9660 -o ro /dev/block/loop4 freedos_img

And there is this the mounted iso at freedos_img

Answer 3

Just came across this. I was having the same issue. You could just do zcat /proc/config.gz | grep CONFIG_BLK_DEV_LOOP from a terminal emulator. If you get a y, you are good to go.

Answer 4

Here is a shell function to check for loop support without creating a loop device. It should even work as non-root.

function check_loop_support {
    local tmp

    # assuming that losetup -f works ... to be checked somewhere else
    tmp=$(losetup -f 2>/dev/null)
    if test -b "$tmp"; then
        return 0
    fi

    # So far we haven't found any loop support. Let's check whether we
    # could load the module and assume that it would work.
    modprobe --quiet --dry-run loop &>/dev/null
    return $?
}

Note there exist losetup versions with different behavior of -f. Sometimes they would automatically load loop module if needed and possible. And some versions would even directly return 1 if no loop support available. Others just print "/dev/loop0" although there is no such device. The function above tries to be safe for all known cases.

Note that you may still need to load the loop module to have usable loop devices available. If you are root you could also run a real "modprobe loop" before losetup to be sure.

Answer 5

You can use Loop device checker to check if your device supports it.