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doc: Add "Initial RAM Disk" section.

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* doc/guix.texi (Initial RAM Disk): New node.
* gnu/system/linux-initrd.scm (expression->initrd): Adjust docstring.
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Ludovic Courtès 2014-07-17 17:49:34 +02:00
parent a1906758c3
commit fd1b1fa296
2 changed files with 78 additions and 5 deletions
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71
doc/guix.texi
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@ -2847,6 +2847,7 @@ instance to support new system services.
* File Systems:: Configuring file system mounts.
* User Accounts:: Specifying user accounts.
* Services:: Specifying system services.
* Initial RAM Disk:: Linux-Libre bootstrapping.
* Invoking guix system:: Instantiating a system configuration.
* Defining Services:: Adding new service definitions.
@end menu
@ -3259,6 +3260,76 @@ password. When @var{auto-login?} is true, log in automatically as
@end deffn
@node Initial RAM Disk
@subsection Initial RAM Disk
@cindex initial RAM disk (initrd)
@cindex initrd (initial RAM disk)
For bootstrapping purposes, the Linux-Libre kernel is passed an
@dfn{initial RAM disk}, or @dfn{initrd}. An initrd contains a temporary
root file system, as well as an initialization script. The latter is
responsible for mounting the real root file system, and for loading any
kernel modules that may be needed to achieve that.
The @code{initrd} field of an @code{operating-system} declaration allows
you to specify which initrd you would like to use. The @code{(gnu
system linux-initrd)} module provides two ways to build an initrd: the
high-level @code{base-initrd} procedure, and the low-level
@code{expression->initrd} procedure.
The @code{base-initrd} procedure is intended to cover most common uses.
For example, if you want to add a bunch of kernel modules to be loaded
at boot time, you can define the @code{initrd} field of the operating
system declaration like this:
@example
(initrd (cut base-init <>
#:extra-modules '("my.ko" "modules.ko")))
@end example
It also handles common use cases that involves using the system as a
QEMU guest, or as a ``live'' system whose root file system is volatile.
@deffn {Monadic Procedure} base-initrd @var{file-systems} @
[#:qemu-networking? #f] [#:virtio? #f] [#:volatile-root? #f] @
[#:extra-modules '()]
Return a monadic derivation that builds a generic initrd. @var{file-systems} is
a list of file-systems to be mounted by the initrd, possibly in addition to
the root file system specified on the kernel command line via @code{--root}.
When @var{qemu-networking?} is true, set up networking with the standard QEMU
parameters. When @var{virtio?} is true, load additional modules so the initrd can
be used as a QEMU guest with para-virtualized I/O drivers.
When @var{volatile-root?} is true, the root file system is writable but any changes
to it are lost.
The initrd is automatically populated with all the kernel modules necessary
for @var{file-systems} and for the given options. However, additional kernel
modules can be listed in @var{extra-modules}. They will be added to the initrd, and
loaded at boot time in the order in which they appear.
@end deffn
Needless to say, the initrds we produce and use embed a
statically-linked Guile, and the initialization program is a Guile
program. That gives a lot of flexibility. The
@code{expression->initrd} procedure builds such an initrd, given the
program to run in that initrd.
@deffn {Monadic Procedure} expression->initrd @var{exp} @
[#:guile %guile-static-stripped] [#:name "guile-initrd"] @
[#:modules '()] [#:to-copy '()] [#:linux #f] @
[#:linux-modules '()]
Return a derivation that builds a Linux initrd (a gzipped cpio archive)
containing @var{guile} and that evaluates @var{exp}, a G-expression,
upon booting.
@var{linux-modules} is a list of @file{.ko} file names to be copied from
@var{linux} into the initrd. @var{to-copy} is a list of additional
derivations or packages to copy to the initrd. @var{modules} is a list
of Guile module names to be embedded in the initrd.
@end deffn
@node Invoking guix system
@subsection Invoking @code{guix system}

12
gnu/system/linux-initrd.scm
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@ -57,11 +57,13 @@ (define* (expression->initrd exp
(to-copy '())
(linux #f)
(linux-modules '()))
"Return a package that contains a Linux initrd (a gzipped cpio archive)
containing GUILE and that evaluates EXP upon booting. LINUX-MODULES is a list
of `.ko' file names to be copied from LINUX into the initrd. TO-COPY is a
list of additional derivations or packages to copy to the initrd. MODULES is
a list of Guile module names to be embedded in the initrd."
"Return a derivation that builds a Linux initrd (a gzipped cpio archive)
containing GUILE and that evaluates EXP, a G-expression, upon booting.
LINUX-MODULES is a list of '.ko' file names to be copied from LINUX into the
initrd. TO-COPY is a list of additional derivations or packages to copy to
the initrd. MODULES is a list of Guile module names to be embedded in the
initrd."
;; General Linux overview in `Documentation/early-userspace/README' and
;; `Documentation/filesystems/ramfs-rootfs-initramfs.txt'.