How to run without a --rootpath

[rossburton]

I'm building an image which doesn't have any root filesystems to populate: it's all firmware binaries and a kernel with initramfs. However, I still need to either have a root directory or set --rootpath to an empty directory.

Is there a way in the config file to tell genimage that it doesn't need to copy any files?

[Harvie]

Yes! This is so much needed. I have prebuilt everything (debootstrap, blobs, bootloaders, etc...) in separate directories and i find it really annoying that genimage forces me to copy that to some --tmp directory. Can't you just take the files from where they already are?

This rootpat/mountpoint concept seems unnecessary to me.

I just want to eg. build ext4 filesystem from files which are already prepared in directory which i want to specify as relative path to genimage.cfg or current working directory. That is all i need, but it is not possible at the moment.

genimage instead forces me to copy all files from rootpath to tmp even when some of these files don't make sense to be copied at all.

[Harvie]

I kinda found an ugly workaround:

Config like this:

image image.cpio {
  cpio {
    format = "crc"
    extraargs = "-L"
  }
  mountpoint = "/../../image_contents"
}

Run like this:

mkdir "fake_empty_root"
./genimage --rootpath "./fake_empty_root" --inputpath "." --outputpath "."

This will

• Create empty directory fake_empty_root and consider it root
• Copy that empty directory to tmp directory
• Run cpio to include tmp/root/../../image_contents
• That way nothing is copied to tmp, but files in ./image_contents/ get in image.cpio

This is ugly but seems to work. But i would expect such functionality to be available without weird hacks.

update: this seems to work with CPIO, but not with EXT4 :-(

[Harvie]

I suggest that we add some new parameter, eg. srcdir which will be able to override whatever path is generated by rootpath+mountpoint combo. so that user can have full control if it's needed.

[Harvie]

Turned out to be very simple to implement. I've made PR, so we can discuss real code. Probably might want to update README to reflect the change and come up with something better than srcdir, exact name of parameter can be changed easily.

[michaelolbrich]

Hmm, I didn't test it but I think the problem with rootpath is in collect_mountpoints(). It should be possible to change this and only require the rootpath when at least one filesystem needs it.

Maybe set image->empty to true for stuff like hdimage and anything else that doesn't need the rootpath. And check for that and whatever we do in #184 to check if rootpath is actually needed.

[michaelolbrich]

With the current master, --rootpath is now optional if:

• none of the images actually need it, such as hd images etc.
• an image that would use it has an explicit srcpath specified.

[rossburton]

That commit doesn't solve the issue I raised though. If I have a pack.config which is about as minimal as possible:

image pack.img {
    hdimage {
        partition-table-type = "none"
    }
    partition 1 {
        image = "file1"
    }
}

Where file1 is a file on disk, I still need to create or pass --rootpath:

$ genimage --config pack.config --inputpath .
INFO: cmd: "mkdir -p "/home/ross/Code/drive-by/genimage/tmp"" (stderr):
INFO: cmd: "rm -rf "/home/ross/Code/drive-by/genimage/tmp"/*" (stderr):
INFO: cmd: "mkdir -p "/home/ross/Code/drive-by/genimage/tmp"" (stderr):
INFO: cmd: "cp -a "/home/ross/Code/drive-by/genimage/root" "/home/ross/Code/drive-by/genimage/tmp/root"" (stderr):
cp: cannot stat '/home/ross/Code/drive-by/genimage/root': No such file or directory

[rossburton]

@michaelolbrich your comment appeared whilst I was adding my comment. Why does my example still need rootpath?

[michaelolbrich]

Are you sure that you have the latest master? I just tested your config and it works as expected.

[rossburton]

Tried again, and it turns out I failed to install the new binary. 🤦