Add support for erofs filesystems

Since Linux 5.4 a new read-only filesystem is available, erofs.
Compared to squashfs it offers much better read performance with and
without compression enabled.
It suppports two optional compressors, lz4 and lz4hc.

>From the mkfs.erofs man page:
EROFS is a new enhanced lightweight linux read-only filesystem with
modern designs (eg. no buffer head, reduced metadata, inline
xattrs/data, etc.) for scenarios which need high-performance read-only
requirements, e.g. Android OS for smartphones and LIVECDs.
It also provides fixed-sized output compression support, which improves
storage density, keeps relatively higher compression ratios, which is
more useful to achieve high performance for embedded devices with
limited  memory since it has unnoticable memory overhead and page cache
thrashing.

This commit adds support for three new filesystem targets:
erofs: erofs without compression
erofs-lz4: erofs with lz4 compresssion enabled
erofs-lz4hc: erofs with lz4hc compression enabled

(From OE-Core rev: 41dead1ff8ccc49e6cd6e6f5d41a59d164693e0d)

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/plugins/source/rawcopy.py

@@ -29,9 +29,9 @@ class RawCopyPlugin(SourcePlugin):
             cmd = 'btrfs filesystem label %s %s' % (dst, label)
         elif fstype == 'swap':
             cmd = 'mkswap -L %s %s' % (label, dst)
-        elif fstype == 'squashfs':
-            raise WicError("It's not possible to update a squashfs "
-                           "filesystem label '%s'" % (label))
+        elif fstype in ('squashfs', 'erofs'):
+            raise WicError("It's not possible to update a %s "
+                           "filesystem label '%s'" % (fstype, label))
         else:
             raise WicError("Cannot update filesystem label: "
                            "Unknown fstype: '%s'" % (fstype))