Op 08-03-2020 om 16:39 schreef Ferry Toth:
Hi
Op 07-03-2020 om 22:21 schreef Ferry Toth:
I am generating a btrfs system image using Yocto.
I want to take a snapshot from the image preferably inside a Yocto
recipe. The snapshot I can send 'over the air' to the remote (IoT)
device.
Now I am able to loop mount the image file using udisksctl as an
ordinary user, which mounts the image under /media/ferry.
However, the owner of the mount point is root, and it appears I am not
allowed to take a snapshot as an ordinary user.
To clarify, I know that I can chown the mount point after mounting.
But to do that I need to sudo it.
I found a way to own the mount point. The procedure is:
1) create an ext34 file system with
EXTRA_IMAGECMD_ext3 += " -E root_owner=`/bin/ps -o user= -p $$`:`/bin/ps
-o group= -p $$`"
Yocto runs the image generation under pseudo (alternative fakeroot). The
above allows to create an ext3 file system with the root owned by the
real current user.
2) btrfs-convert the ext3 image to btrfs
3) take the snapshot
The final step (btrfs send) fails with:
ERROR: check if we support uuid tree fails - Operation not permitted
ERROR: failed to initialize subvol search: Operation not permitted
It appears it just can't be done currently as I could have from:
https://webcache.googleusercontent.com/search?q=cache:oZR58gPBVRkJ:https://www.spinics.net/lists/linux-btrfs/msg31188.html+&cd=1&hl=en&ct=clnk&gl=nl&client=ubuntu
HOSTTOOLS += " /usr/bin/udisksctl /bin/btrfs /bin/btrfs-convert /bin/ps"
# we are running as pseudo but we need ownership of the root as the real
user
EXTRA_IMAGECMD_ext3 += " -E root_owner=`/bin/ps -o user= -p $$`:`/bin/ps
-o group= -p $$`"
IMAGE_FSTYPES += " ext3"
python do_btrfs_snapshot() {
import subprocess
# convert the ext3 image
cmd_mkimg = 'btrfs-convert ' +
d.expand("${DEPLOY_DIR_IMAGE}/${IMAGE_BASENAME}-${MACHINE}.ext3")
ret = subprocess.run(cmd_mkimg, shell=True, capture_output=True,
text=True)
# mount the converted ext3 image
cmd_mkimg = '/usr/bin/udisksctl loop-setup --no-user-interaction -f
' + d.expand("${DEPLOY_DIR_IMAGE}/${IMAGE_BASENAME}-${MACHINE}.ext3")
ret = subprocess.run(cmd_mkimg, shell=True, capture_output=True,
text=True)
loop = ret.stdout.split(' ').pop().split('.')[0]
# find the mounted partition
cmd_mkimg = 'lsblk -o MOUNTPOINT -n ' + loop
ret = subprocess.run(cmd_mkimg, shell=True, capture_output=True,
text=True)
mount_point = ret.stdout.rstrip()
# take a snapshot of the partition
cmd_mkimg = '/bin/btrfs su snap -r ' + mount_point + ' ' +
mount_point + '/@new'
print(cmd_mkimg)
ret = subprocess.run(cmd_mkimg, shell=True, capture_output=True,
text=True)
# btrfs send the partition
cmd_mkimg = '/bin/btrfs send ' + mount_point + '/@new/ > ' +
d.expand("${DEPLOY_DIR_IMAGE}/${IMAGE_BASENAME}-${MACHINE}.snapshot")
ret = subprocess.run(cmd_mkimg, shell=True, capture_output=True,
text=True)
print(ret.stdout)
print(ret.stderr)
# unmount the btrfs image
cmd_mkimg = '/usr/bin/udisksctl unmount -b ' + loop
ret = subprocess.run(cmd_mkimg, shell=True, capture_output=True,
text=True)
# delete the loop device
cmd_mkimg = '/usr/bin/udisksctl loop-delete -b ' + loop
ret = subprocess.run(cmd_mkimg, shell=True, capture_output=True,
text=True)
return 0
}
addtask btrfs_snapshot after image_ext3 before do_bootimg
I think it is obvious that I don't want to run bitbake as root.
So what is the recommended way to generate a snapshot without becoming
root?
Thanks,
Ferry
