[Vmdebootstrap-devel] Bug#741223: vmdebootstrap: please support root on btrfs

[Petter Reinholdtsen]

I had another look at setting up a root file system on a btrfs subvolume
now that vmdebootstrap support grub, and freshed up the patch to give it
another go.

Unfortunately, grub is not able to find / when it is a btrfs subvolume:

# vmdebootstrap --roottype btrfs --image=test.img --verbose --grub --bootsize=256M
Creating disk image
Creating partitions
Creating filesystem btrfs
Mounting /dev/mapper/loop0p2 on /tmp/tmpAtr8MZ
Creating filesystem ext2
Mounting /dev/mapper/loop0p1 on /tmp/tmpAtr8MZ/@/boot/
Debootstrapping
Give root an empty password
Removing udev persistent cd and net rules
Setting up networking
Updating the initramfs
Configuring grub2
command failed: ['chroot', '/tmp/tmpAtr8MZ/@', 'update-grub']

/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).

Failed. Is grub2-common installed? Using extlinux.
Installing extlinux
Cleaning up
#

The resulting image were not able to boot.

This is the patch I used:

--- vmdebootstrap.orig	2014-10-18 20:35:19.000000000 +0200
+++ vmdebootstrap	2014-11-01 21:40:56.046766661 +0100
@@ -39,6 +39,9 @@
         self.settings.boolean(['verbose'], 'report what is going on')
         self.settings.string(['image'], 'put created disk image in FILE',
                              metavar='FILE')
+        self.settings.string(['roottype'],
+                             'specify file system type for /',
+                             default='ext4')
         self.settings.bytesize(['size'],
                                'create a disk image of size SIZE (%default)',
                                metavar='SIZE',
@@ -129,7 +132,7 @@
 
         try:
             rootdev = None
-            roottype = 'ext4'
+            roottype = self.settings['roottype']
             bootdev = None
             boottype = None
             rootdir = None
@@ -141,6 +144,15 @@
                 (rootdev, bootdev) = self.setup_kpartx()
                 self.mkfs(rootdev, type=roottype)
                 rootdir = self.mount(rootdev)
+                rootfsdir = rootdir
+                if 'btrfs' == roottype:
+                    self.settings['package'].append("btrfs-tools")
+                    # Put root in a subvolume, to ease snapshots and volume management
+                    newrootdir = "%s/@" % rootdir
+                    self.runcmd(['btrfs', 'subvolume', 'create', newrootdir])
+                    self.runcmd(['btrfs', 'subvolume', 'set-default', '@', rootdir])
+                    os.mkdir("%s/btrfs" % newrootdir)
+                    rootdir = newrootdir
                 if bootdev:
                     if self.settings['boottype']:
                         boottype = self.settings['boottype']
@@ -168,9 +180,9 @@
 
             if self.settings['image']:
                 if self.settings['grub']:
-                    self.install_grub2(rootdev, rootdir)
+                    self.install_grub2(rootdev, rootdir, rootfsdir)
                 elif self.settings['extlinux']:
-                    self.install_extlinux(rootdev, rootdir)
+                    self.install_extlinux(rootdev, rootdir, rootfsdir)
                 self.append_serial_console(rootdir)
                 self.optimize_image(rootdir)
                 if self.settings['squash']:
@@ -379,7 +391,12 @@
         fstab = os.path.join(rootdir, 'etc', 'fstab')
         with open(fstab, 'w') as f:
             f.write('proc /proc proc defaults 0 0\n')
-            f.write('%s / %s errors=remount-ro 0 1\n' % (rootdevstr, roottype))
+            if 'btrfs' == roottype:
+#                f.write('%s / %s defaults 0 1\n' % (rootdevstr, roottype))
+                f.write('%s / %s subvol=@ 0 1\n' % (rootdevstr, roottype))
+                f.write('%s /btrfs %s defaults 1\n' % (rootdevstr, roottype))
+            else:
+                f.write('%s / %s errors=remount-ro 0 1\n' % (rootdevstr, roottype))
             if bootdevstr:
                 f.write('%s /boot %s errors=remount-ro 0 2\n' % (bootdevstr, boottype))
 
@@ -472,7 +489,8 @@
             with open(inittab, 'a') as f:
                 f.write('\nS0:23:respawn:%s\n' % serial_command)
 
-    def install_grub2(self, rootdev, rootdir):
+    def install_grub2(self, rootdev, rootdir, rootfsdir):
+        # FIXME use rootfsdir
         self.message("Configuring grub2")
         # rely on kpartx using consistent naming to map loop0p1 to loop0
         install_dev = os.path.join('/dev', os.path.basename(rootdev)[:-2])
@@ -486,13 +504,14 @@
             self.runcmd(['chroot', rootdir, 'update-grub'])
             self.runcmd(['chroot', rootdir, 'grub-install', install_dev])
         except cliapp.AppException as e:
+            self.message(str(e))
             self.message("Failed. Is grub2-common installed? Using extlinux.")
         self.runcmd(['umount', os.path.join(rootdir, 'sys')])
         self.runcmd(['umount', os.path.join(rootdir, 'proc')])
         self.runcmd(['umount', os.path.join(rootdir, 'dev')])
-        self.install_extlinux(rootdev, rootdir)
+        self.install_extlinux(rootdev, rootdir, rootfsdir)
 
-    def install_extlinux(self, rootdev, rootdir):
+    def install_extlinux(self, rootdev, rootdir, rootfsdir):
         if not os.path.exists("/usr/bin/extlinux"):
             self.message("extlinux not installed, skipping.")
             return
@@ -519,7 +538,7 @@
                            '-s', 'UUID', rootdev])
         uuid = out.splitlines()[0].strip()
 
-        conf = os.path.join(rootdir, 'extlinux.conf')
+        conf = os.path.join(rootfsdir, 'extlinux.conf')
         logging.debug('configure extlinux %s' % conf)
         f = open(conf, 'w')
         f.write('''
@@ -528,7 +547,7 @@
 
 label linux
 kernel %(kernel)s
-append initrd=%(initrd)s root=UUID=%(uuid)s ro %(kserial)s
+append initrd=%(initrd)s root=UUID=%(uuid)s ro %(kserial)s %(rootflags)s
 %(extserial)s
 ''' % {
             'kernel': kernel_image,
@@ -536,11 +555,12 @@
             'uuid': uuid,
             'kserial':
             'console=ttyS0,115200' if self.settings['serial-console'] else '',
+            'rootflags': 'rootfsflags=subvol=@' if 'btrfs' == self.settings['roottype'] else '',
             'extserial': 'serial 0 115200' if self.settings['serial-console'] else '',
         })
         f.close()
 
-        self.runcmd(['extlinux', '--install', rootdir])
+        self.runcmd(['extlinux', '--install', rootfsdir])
         self.runcmd(['sync'])
         time.sleep(2)
 
-- 
Happy hacking
Petter Reinholdtsen