linux-initrd: Allow use of volume labels in 'file-system' declarations.
* guix/build/linux-initrd.scm (%ext2-endianness, %ext2-sblock-magic,
%ext2-sblock-creator-os, %ext2-sblock-uuid, %ext2-sblock-volume-name):
New macros.
(read-ext2-superblock, ext2-superblock-uuid,
ext2-superblock-volume-name, disk-partitions,
partition-label-predicate, find-partition-by-label,
canonicalize-device-spec): New procedures.
(mount-file-system): Use 'canonicalize-device-spec' on SOURCE.
(boot-system): Likewise for ROOT.
* doc/guix.texi (Using the Configuration System): Adjust 'file-system'
declaration accordingly.
85a83edb36