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docs: migrate boot loader interface from fdo wiki to git 

This imports
https://www.freedesktop.org/wiki/Software/systemd/BootLoaderInterface/
into our sources, and extends it substantially with various variables
now supported.
This commit is contained in:
Lennart Poettering 2018-10-23 16:28:30 +02:00
parent f20db19954
commit 2fe8213230
3 changed files with 81 additions and 7 deletions
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76
docs/BOOT_LOADER_INTERFACE.md Normal file
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# The Boot Loader Interface
systemd can interface with the boot loader to receive performance data and
other information, and pass control information. This is only supported on EFI
systems. Data is transferred between the boot loader and systemd in EFI
variables. All EFI variables use the vendor UUID
`4a67b082-0a4c-41cf-b6c7-440b29bb8c4f`.
* The EFI Variable `LoaderTimeInitUSec` contains the timestamp in microseconds
when the loader was initialized. This value is the time spent in the firmware
for initialization, it is formatted as numeric, NUL-terminated, decimal
string, in UTF-16.
* The EFI Variable `LoaderTimeExecUSec` contains the timestamp in microseconds
when the loader finished its work and is about to execute the kernel. The
time spent in the loader is the difference between `LoaderTimeExecUSec` and
`LoaderTimeInitUSec`. This value is formatted the same way as
`LoaderTimeInitUSec`.
* The EFI variable `LoaderDevicePartUUID` contains the partition GUID of the
ESP the boot loader was run from formatted as NUL-terminated UTF16 string, in
normal GUID syntax.
* The EFI variable `LoaderConfigTimeout` contains the boot menu time-out
currently in use. It may be modified both by the boot loader and by the
host. The value should be formatted as numeric, NUL-terminated, decimal
string, in UTF-16. The time is specified in µs.
* Similarly, the EFI variable `LoaderConfigTimeoutOneShot` contains a boot menu
time-out for a single following boot. It is set by the OS in order to request
display of the boot menu on the following boot. When set overrides
`LoaderConfigTimeout`. It is removed automatically after being read by the
boot loader, to ensure it only takes effect a single time. This value is
formatted the same way as `LoaderConfigTimeout`. If set to `0` the boot menu
time-out is turned off, and the menu is shown indefinitely.
* The EFI variable `LoaderEntries` may contain a series of boot loader entry
identifiers, one after the other, each individually NUL terminated. This may
be used to let the OS know which boot menu entries were discovered by the
boot loader. A boot loader entry identifier should be a short, non-empty
alphanumeric string (possibly containing `-`, too). The list should be in the
order the entries are shown on screen during boot. See below regarding a
recommended vocabulary for boot loader entry identifiers.
* The EFI variable `LoaderEntryDefault` contains the default boot loader entry
to use. It contains a NUL-terminated boot loader entry identifier.
* Similarly, the EFI variable `LoaderEntryOneShot` contains the default boot
loader entry to use for a single following boot. It is set by the OS in order
to request booting into a specific menu entry on the following boot. When set
overrides `LoaderEntryDefault`. It is removed automatically after being read
by the boot loader, to ensure it only takes effect a single time. This value
is formatted the same way as `LoaderEntryDefault`.
* The EFI variable `LoaderEntrySelected` contains the boot loader entry
identifier that was booted. It is set by the boot loader and read by
the OS in order to identify which entry has been used for the current boot.
* The EFI variable `LoaderFeatures` contains a 64bit unsigned integer with a
number of flags bits that are set by the boot loader and passed to the OS and
indicate the features the boot loader supports. Specifically, the following
bits are defined:
* `1 << 0` → The boot loader honours `LoaderConfigTimeout` when set.
* `1 << 1` → The boot loader honours `LoaderConfigTimeoutOneShot` when set.
* `1 << 2` → The boot loader honours `LoaderEntryDefault` when set.
* `1 << 3` → The boot loader honours `LoaderEntryOneShot` when set.
* `1 << 4` → The boot loader supports boot counting as described in [Automatic Boot Assessment](https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT).
If `LoaderTimeInitUSec` and `LoaderTimeExecUSec` are set, `systemd-analyze`
will include them in its boot-time analysis. If `LoaderDevicePartUUID` is set,
systemd will mount the ESP that was used for the boot to `/boot`, but only if
that directory is empty, and only if no other file systems are mounted
there. The `systemctl reboot --boot-loader-entry=…` and `systemctl reboot
--boot-loader-menu=…` commands rely on the `LoaderFeatures` ,
`LoaderConfigTimeoutOneShot`, `LoaderEntries`, `LoaderEntryOneShot` variables.

2
man/bootctl.xml
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<para>
<citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
<ulink url="https://www.freedesktop.org/wiki/Software/systemd/BootLoaderInterface">Boot Loader Interface</ulink>
<ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
</para>
</refsect1>
</refentry>

10
man/systemd-boot.xml
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@ -63,9 +63,8 @@
used from a running system to locate the ESP, list available entries, and install systemd-boot itself.</para>
<para>systemd-boot will provide information about the time spent in UEFI firmware using the <ulink
url="https://www.freedesktop.org/wiki/Software/systemd/BootLoaderInterface">Boot Loader Interface</ulink>. This
information can be displayed using
<citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. This information can be displayed
using <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
</para>
</refsect1>
@ -331,8 +330,7 @@
<listitem><para>Information about the time spent in various parts of the boot loader. Set by the boot
loader. Use <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
to view this data. These variables are defined by the <ulink
url="https://www.freedesktop.org/wiki/Software/systemd/BootLoaderInterface">Boot Loader
Interface</ulink>.</para></listitem>
url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
@ -400,7 +398,7 @@
<citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
<ulink url="https://www.freedesktop.org/wiki/Software/systemd/BootLoaderInterface">Boot Loader Interface</ulink>
<ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
</para>
</refsect1>
</refentry>