[pve-devel] [PATCH container 4/4] Fix #918: add /dev/mapper symlinks for dm-* devices

[Wolfgang Bumiller]

Mount canonicalizes paths unless the -c option is used. This
is mostly fine but for device-mapper nodes (/dev/dm-*) it'll
fetch the /dev/mapper/* path and pass that to the mount
system call resulting in /proc/mounts showing the
/dev/mapper path. This is neither the one we provided (since
we use /dev/$vg/$lv), nor the one userspace tools will find
in /dev currently.
Since the dm-* paths are rather inconvenient to look at we
decided to keep mount's behavior and compensate by providing
the /dev/mapper symlinks for devices via the autodev hook.
---
 src/PVE/LXC.pm           | 5 +++++
 src/lxc-pve-autodev-hook | 7 +++++++
 2 files changed, 12 insertions(+)

diff --git a/src/PVE/LXC.pm b/src/PVE/LXC.pm
index 3ed5d92..3a92f3d 100644
--- a/src/PVE/LXC.pm
+++ b/src/PVE/LXC.pm
@@ -1073,6 +1073,11 @@ sub mountpoint_mount {
 	    }
 	    return wantarray ? ($path, 0, undef) : $path;
 	} elsif ($format eq 'raw' || $format eq 'iso') {
+	    # NOTE: 'mount' performs canonicalization without the '-c' switch, which for
+	    # device-mapper devices is special-cased to use the /dev/mapper symlinks.
+	    # Our autodev hook expects the /dev/dm-* device currently
+	    # and will create the /dev/mapper symlink accordingly
+	    ($path) = (Cwd::realpath($path) =~ /^(.*)$/s); # realpath() taints
 	    my $domount = sub {
 		my ($path) = @_;
 		if ($mount_path) {
diff --git a/src/lxc-pve-autodev-hook b/src/lxc-pve-autodev-hook
index efc82a2..2e2f998 100755
--- a/src/lxc-pve-autodev-hook
+++ b/src/lxc-pve-autodev-hook
@@ -53,6 +53,13 @@ while (defined(my $line = <$fd>)) {
 
     PVE::Tools::run_command(['mknod', '-m', '666', "$root/dev/$dev",
                              $type, $major, $minor]);
+
+    if ($dev =~ /^dm-\d+$/) {
+	File::Path::mkpath("$root/dev/mapper");
+	my $mapped_name = PVE::Tools::file_get_contents("/sys/block/$dev/dm/name");
+	chomp $mapped_name;
+	symlink("/dev/$dev", "$root/dev/mapper/$mapped_name");
+    }
 }
 close $fd;
 
-- 
2.1.4