flash-kernel
------------

flash-kernel is a script which will put the kernel and initramfs in
the boot location of embedded devices that don't load the kernel and
initramfs directly from /boot.  flash-kernel supports devices that
boot from flash memory (hence the name) as well as some devices that
require a special boot image on the disk.

Check the Database file db/all.db (in the source package) or
/usr/share/flash-kernel/db/all.db (in the installed package) for supported
machines.

If you would like to see support for another device, please file a bug
report in the Debian Bug Tracking System and include all information
related to the boot process of your device.  Instructions can be found
at https://bugs.debian.org/ . Alternatively prepare a Merge Request on
https://salsa.debian.org/ .


Testsuite
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Run the testsuite with:
    FK_CHECKOUT=. ./test_db
    FK_CHECKOUT=. ./test_flash-kernel
    FK_CHECKOUT=. ./test_functions

You need the devscripts package for the checkbashisms test.


Database format
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To accommodate the differences between machines, db/*.db files contain
information on supported machines.  The files look somewhat like
RFC 2822 data or Debian control data, i.e. header: value pairs,
with definitions separated by an empty line.  Comments starting with a
pound are ignored.

/etc/flash-kernel/db is parsed first and allows for local override of
any field. Note that you must include the "Machine" field (including
multiple instances if necessary) here as well as the field(s) to be
overridden.

The supported fields are:

* Machine: (required) value of the "Hardware:" line in /proc/cpuinfo
  or content of /proc/device-tree/model. Used as a unique
  identifier. Must be the first field in each stanza. There can be
  multiple instances of this field (to support system which have both
  cpuinfo:Hardware and device-tree based identifiers depending on the
  current kernel) but all instances of the Machine: field must come
  before any other field in the stanza.

* Kernel-Flavors: (optional) allowed flavors (suffixes) for the to be
  installed kernel; if the vmlinuz file doesn't end with a listed
  suffix, installation is aborted

* Machine-Id: (optional) linux mach-type to set before starting vmlinuz;
  will be set by a small piece of ARM code prepended to the kernel image.
  This option is ignored if a DTB is to be appended, via either DTB-Append or
  DTB-Append-From.

* DTB-Id: (optional) specifies the name of the DTB file for this device.
  If DTB-Id specifies an absolute path the directory specifies the path from
  where the DTB is copied.
  If DTB-Id specifies a relative path the directory specifies the subdirectory
  of the kernel version directory where the DTB will be installed.
  The filename is used to search for the filename in subdirectories of
  /usr/lib/linux-image-* or /etc/flash-kernel/dtbs.
  If the value begins with a `!' then the field is a script which should be
  run. The script must produce the DTB filename (possibly including a
  directory) on stdout.

* DTB-Append: (optional) when yes the DTB specified by DTB-Id will be appended
  to the kernel image.

* DTB-Append-From: (optional): Can be used instead of DTB-Append. The argument
  is a kernel version, if the kernel to be installed is at least this version
  then the DTB specified named by DTB-Id will be appended to the kernel image.
  When adding or updating this field remember to consider whether the kernel
  will require an update to its versioned Breaks: on flash-kernel.

* U-Boot-Kernel-Address, U-Boot-Kernel-Entry-Point, U-Boot-Initrd-Address:
  (optional) address where to load in (physical) RAM the kernel, entry point
  and initrd, respectively; this also indicates that U-Boot images should be
  generated with mkimage

* U-Boot-Script-Address: (optional) like U-Boot-Kernel-Address and
  U-Boot-Initrd-Address but for an U-Boot boot script; see also
  U-Boot-Script-Name

* U-Boot-Script-Name: (optional) name of U-Boot boot script to install
  from the flash-kernel files. @@KERNEL_VERSION@@ will be substituted for the
  actual kernel version

* Boot-Kernel-Path, Boot-Initrd-Path: (optional) where to put the
  generated kernel and initrd files on the filesystem; see also
  Boot-Device

* Boot-Kernel-Path-Version, Boot-Initrd-Path-Version, Boot-DTB-Path-Version:
  (optional) if "yes" appends the kernel version to files created with
  Boot-Kernel-Path, Boot-Initrd-Path and Boot-DTB-Path.

* Boot-Script-Path: (optional) like Boot-Kernel-Path and
  Boot-Initrd-Path but for an U-Boot boot script; see also
  U-Boot-Script-Name and Boot-Device

* Boot-DTB-Path: (optional) like Boot-Kernel-Path and Boot-Initrd-Path
  but for a DTB file. The DTB file named by DTB-Id will be copied
  here; see also DTB-Id

* Mtd-Kernel, Mtd-Initrd: (optional) Specifies the raw MTD partition
  name (per /proc/mtd) to use for the kernel and initrd respectively.

* Required-Packages: (optional) list of packages which must be added
  during installer phase for flash-kernel to work properly; failure to
  add these packages aborts the installation

* Optional-Packages: (optional) list of packages which should be
  added during installer phase for flash-kernel to offer full
  functionality; failure to add these packages just triggers a warning

* Bootloader-Sets-Incorrect-Root: (optional) when "yes" indicates that
  the bootloader passes a root= value to the kernel and that this
  should be overridden in the initrd; when "no", flash-kernel only sets
  a default value for the root device, which allows end-users to pass
  root= to the kernel.

* Method: (optional) indicates how to support this particular machine;
  the default is "generic"; other available methods are: android, bootspec,
  multi, redboot, slug, symlink and olpc

* Boot-Device: (optional) block device to mount before installing
  kernel,  initrd and U-Boot script; Boot-Kernel-Path, Boot-Initrd-Path and
  Boot-Script-Path are then taken relative to this boot device


Configuration
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Configuration files currently supported:
* /etc/flash-kernel/machine allows skipping the machine auto-detection from
  /proc/cpuinfo or /proc/dtmodel and forcing a specific Machine.

* /etc/flash-kernel/db allows overriding / adding fields from the Machine
  database (but it doesn't allow removing fields or entries).

* /etc/flash-kernel/dtbs (directory). If a DTB matching DTB-Id is
  found here then it will be used in preference to the one shipped by
  the kernel being installed.

* /etc/flash-kernels/bootscript (directory). The files referenced via
  the Boot-Script-Name field are installed here.

* /etc/flash-kernel/ubootenv.d and /etc/flash-kernel/preboot.d can be used to
  add or override u-boot script snippets. See "Adding U-Boot Commands for
  Pre-Boot Execution" below for more details.

* /etc/default/flash-kernel currently contains the following variables:
    - LINUX_KERNEL_CMDLINE, which should be used by bootscripts to set kernel
      options, overriding the firmwares defaults (e.g. u-boot's ${bootargs}).
    - LINUX_KERNEL_CMDLINE_DEFAULTS, which should be used by bootscripts to set
      kernel options which should be overrideable by the firmware's defaults
      (e.g. u-boot's ${bootargs}).
    - NO_CREATE_DOT_BAK_FILES, which if set to "true" or "yes" will
      prevent flash-kernel from creating backup ".bak" versions of
      kernel, initrd, and dtb files when installing a new version. The
      default is to create such backups to aid in recovery from
      failed updates. If this option is enabled then more complex
      methods or specialised hardware (e.g. JTAG) may be required to
      recover.
    - MTD_BACKUP_DIR, which if set, names a directory to which
      flash-kernel will write copies of files which would not normally
      be accessible in the regular filesystem (either written to a
      rawflash partition or to a firmware partition which is not
      normally mounted). If unset defaults to
      /var/backups/flash-kernel. Set to "none" to disable.

Adding U-Boot Commands for Pre-Boot Execution
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Packages can drop in files containing U-Boot commands to be executed by a
platform's bootscript before starting the OS. These files should be
dropped in /usr/share/flash-kernel/ubootenv.d and
/usr/share/flash-kernel/preboot.d. Users can add additional
stubs, or override stubs provided by packages, by adding files to
/etc/flash-kernel/ubootenv.d and /etc/flash-kernel/preboot.d. Files in the
/etc path that have the same name as files in the /usr path will override the
/usr counterparts.

Platform bootscripts must contain the @@UBOOT_ENV_EXTRA@@ and
@@UBOOT_PREBOOT_EXTRA@@ macros for the contents of these stubs to be
incorporated.
