linux-initrd: Ensure that the guile used in the initrd is referenced.

By referencing guile from the initrd output explicitly, it will be present in
the store when this initrd is used. If the exact guile used within the initrd
isn't present in the store, then after root is switched during the boot
process, loading modules (such as (ice-9 popen)) won't work.

This fixes guix-patches bug #28399, "Fix mysql activation, and add a basic
test".

* gnu/system/linux-initrd.scm (expression->initrd)[builder]: Write out a file
  called references in to the initrd output, which includes the store path for
  guile.

Merge branch 'master' into staging

file-systems: Add a 'location' field to <file-system>.

* gnu/system/file-systems.scm (<file-system>)[location]: New field.

uuid: Add 'uuid=?' and use it.

* gnu/system/uuid.scm (uuid=?): New procedure.
* tests/uuid.scm ("uuid=?"): New test.
* gnu/build/file-systems.scm (partition-uuid-predicate)
(luks-partition-uuid-predicate): Use it instead of 'bytevector=?'.

Merge branch 'master' into staging

vm: Add disk-image-size to <virtual-machine>.

* gnu/system/vm.scm (<virtual-machine>): Add disk-image-size.
  (port-forwardings->qemu-options): Use disk-image-size from
  <virtual-machine>.

vm: Add a minimum root size.

* gnu/system/vm.scm (qemu-image): When guessing the root-size, use a lower
  bound of 20 MiB, otherwise the root file system size is sometimes 0 MiB in
  size.

Merge branch 'master' into staging

uuid: Add a parser for FAT32 UUIDs.

* gnu/system/uuid.scm (%fat32-uuid-rx): New variable.
(string->fat32-uuid): New procedure.
(%uuid-parsers): Add it.
* tests/uuid.scm ("uuid, FAT32, format preserved"): New test.

services: Move 'session-environment-service-type' to pam.scm.

* gnu/services/base.scm (environment-variables->environment-file)
(session-environment-service-type)
(session-environment-service): Move to...
* gnu/system/pam.scm: ... here.

Merge branch 'master' into staging

doc: Use Screen and OpenSSH in the bare-bones example.

* gnu/system/examples/bare-bones.tmpl (packages): Remove TCPDUMP; add
SCREEN and OPENSSH.
* doc/guix.texi (Using the Configuration System): Adjust explanation
accordingly.

install: Include the whole bare-bones OS in the image.

* gnu/system/install.scm (%installation-services): Load
"example/bare-bones.tmpl".  Add a 'gc-root-service-type' instance.

vm: Generate a UUID to identify the root file system.

This makes collisions less likely than when using a label to look up the
partition.  See <https://bugs.gnu.org/27735>.

* gnu/system/vm.scm (operating-system-uuid): New procedure.
(system-disk-image): Define 'root-uuid' and use it for the root file
system.  Pass it to 'iso9660-image' and 'qemu-image'.

vm: Allow users to specify a UUID for the root partition.

* gnu/system/vm.scm (qemu-image): Add #:file-system-uuid parameter; pass
it as the 'uuid' field of the root partition.

uuid: 'uuid' macro supports more UUID types.

* gnu/system/uuid.scm (string->uuid): Turn 'type' into an optional
argument.
(uuid): Add clauses to allow for an optional 'type' parameter.

system: Introduce a disjoint UUID type.

Conceptually a UUID is just a bytevector.  However, there's software out
there such as GRUB that relies on the string representation of different
UUID types (e.g., the string representation of DCE UUIDs differs from
that of ISO-9660 UUIDs, even if they are actually bytevectors of the
same length).  This new <uuid> record type allows us to preserve
information about the type of UUID so we can eventually convert it to a
string using the right representation.

* gnu/system/uuid.scm (<uuid>): New record type.
(bytevector->uuid): New procedure.
(uuid): Return calls to 'make-uuid'.
(uuid->string): Rewrite using 'match-lambda*' to accept a single 'uuid?'
argument.
* gnu/bootloader/grub.scm (grub-root-search): Check for 'uuid?' instead
of 'bytevector?'.
* gnu/system.scm (bootable-kernel-arguments): Check whether ROOT-DEVICE
is 'uuid?'.
(read-boot-parameters): Use 'bytevector->uuid' when the
store device is a bytevector.
(read-boot-parameters-file): Check for 'uuid?' instead of 'bytevector?'.
(device->sexp): New procedure.
(operating-system-boot-parameters-file): Use it for 'root-device' and
'store'.
(operating-system-bootcfg): Remove conditional in definition of
'root-device'.
* gnu/system/file-systems.scm (file-system->spec): Check for 'uuid?' on
DEVICE and take its bytevector.
* gnu/system/mapped-devices.scm (open-luks-device): Likewise.
* gnu/system/vm.scm (iso9660-image): Call 'uuid-bytevector' for the
 #:volume-uuid argument.

file-systems: Introduce (gnu system uuid).

* gnu/build/file-systems.scm (sub-bytevector)
(latin1->string, %fat32-endianness, fat32-uuid->string)
(%iso9660-uuid-rx, string->iso9660-uuid)
(iso9660-uuid->string, %network-byte-order)
(dce-uuid->string, %uuid-rx, string->dce-uuid)
(string->ext2-uuid, string->ext3-uuid, string->ext4-uuid)
(vhashq, %uuid-parsers, %uuid-printers, string->uuid)
(uuid->string): Move to...
* gnu/system/uuid.scm: ... here.  New file.
* gnu/system/file-systems.scm (uuid): Move to the above file.
* gnu/system/vm.scm: Adjust accordingly.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add uuid.scm.

install: Add OpenSSH to the global profile.

Suggested by Jan Nieuwenhuizen.

* gnu/system/install.scm (installation-os)[packages]: Add OPENSSH.

install: Add 'passwd' to $PATH.

Suggested by Jan Nieuwenhuizen.

* gnu/system/install.scm (installation-os)[setuid-programs]: Add 'passwd'.