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docs: add new "sort-key" field to boot loader spec

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This allows snippet generators to explicitly order entries: any string
can be set as an entry's "sort key". If set, sd-boot will use it to sort
entries on display.

New logic is hence (ignore the boot counting logic)

  sort-key is set → primary sort key: sort-key (lexicographically increasing order)
                  → secondary sort key: machine-id (also increasing order)
                  → tertiary sort key: version (lexicographically decreasing order!)

  sort-key is not set → primary sort key: entry filename (aka id), lexicographically increasing order)

With this scheme we can order OSes by their names from A-Z but then put
within the same OS still the newest version first. This should clean up
the order to match expectations more.

Based on discussions here:

https://github.com/systemd/systemd/pull/22391#issuecomment-1040092633
This commit is contained in:
Lennart Poettering 2022-02-15 14:19:40 +01:00
parent f65a33269e
commit 1011935785
1 changed files with 16 additions and 5 deletions
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21
docs/BOOT_LOADER_SPECIFICATION.md
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@ -232,6 +232,16 @@ spaces from its value. The following keys are known:
other installed operating systems. This ID shall be formatted as 32 lower
case hexadecimal characters (i.e. without any UUID formatting). This key is
optional. Example: `4098b3f648d74c13b1f04ccfba7798e8`.
* `sort-key` shall contain a short string used for sorting entries on
display. This can be defined freely though should typically be initialized
from `IMAGE_ID=` or `ID=` from `/etc/os-release` of the relevant entry,
possibly suffixed. This field is optional. If set, it is used as primary
sorting key for the entries on display (lexicographically increasing). It
does not have to be unique (and usually is not). If non-unique the the
`machine-id` (lexicographically increasing) and `version` (lexicographically
decreasing, i.e. newest version first) fields described above are used as
secondary/ternary sorting keys. If this field is not set entries are
typically sorted by the `.conf` file name of the entry.
* `linux` refers to the Linux kernel to spawn and shall be a path relative to
`$BOOT`. It is recommended that every distribution creates a machine id and
version specific subdirectory below `$BOOT` and places its kernels and
@ -269,8 +279,9 @@ key and is otherwise not valid. Here's an example for a complete drop-in file:
# /boot/loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf
title Fedora 19 (Rawhide)
version 3.8.0-2.fc19.x86_64
sort-key fedora
machine-id 6a9857a393724b7a981ebb5b8495b9ea
version 3.8.0-2.fc19.x86_64
options root=UUID=6d3376e4-fc93-4509-95ec-a21d68011da2
architecture x64
linux /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux
@ -358,10 +369,10 @@ simply reads all files `$BOOT/loader/entries/*.conf`, and populates its boot
menu with this. On EFI, it then extends this with any unified kernel images
found in `$BOOT/EFI/Linux/*.efi`. It may also add additional entries, for
example a "Reboot into firmware" option. Optionally it may sort the menu based
on the `machine-id` and `version` fields, and possibly others. It uses the file
name to identify specific items, for example in case it supports storing away
default entry information somewhere. A boot loader should generally not modify
these files.
on the `sort-key`, `machine-id` and `version` fields, and possibly others. It
uses the file name to identify specific items, for example in case it supports
storing away default entry information somewhere. A boot loader should
generally not modify these files.
For "Boot Loader Specification Entries" (Type #1), the _kernel package
installer_ installs the kernel and initrd images to `$BOOT` (it is recommended