prairiedog: treat value-less key differently than "empty" values

[etungsten]

Issue number:

Resolves #2359

Description of changes:

    prairiedog: treat value-less key differently than "empty" values
    
    Before this change, prairedog did no special handling for value-less
    bootconfig keys and would just write out 'key ='. The kernel is
    insensitive to whitespace so it would grab the next k/v from the
    bootconfig and substitute it for the value.
    
    With this change, prairiedog now differentiates between value-less keys
    and keys with empty values (e.g. 'key = ""') both in parsing an existing
    bootconfig file as well as when it generates the bootconfig initrd from
    existing settings.
    
    When the key is value-less, prariedog will just write out the key
    without '=' for its line entry in the bootconfig (e.g. just 'key').

Testing done:
The new unit test passes.
Built aws-k8s-1.23 and passed the following user-data:

[settings.boot.kernel-parameters]
"console" = [
    "tty0",
    "ttyS1,115200n8",
]
"crashkernel" = [
    "2G-:256M",
]
"slub_debug" = [
    "options,slabs",
]
"usbcore.quirks" = [
    "0781:5580:bk",
    "0a5c:5834:gij",
]
[settings.boot.init-parameters]
"log_level" = ["debug"]
"splash" = []

Host comes up fine. Prairiedog writes out the bootconfig as expected. Note how init.splash is value-less:

bash-5.1# cat /var/lib/bottlerocket/bootconfig.data                                                      
kernel.crashkernel = "2G-:256M"                                                                          
kernel.slub_debug = "options,slabs"                                                                      
kernel.usbcore.quirks = "0781:5580:bk", "0a5c:5834:gij"                                                  
kernel.console = "tty0", "ttyS1,115200n8"                                                                
init.log_level = "debug"                                                                                 
init.splash          

After a reboot, kernel interprets the bootconfig correctly:

bash-5.1# cat /proc/bootconfig 
kernel.console = "tty0", "ttyS1,115200n8"
kernel.crashkernel = "2G-:256M"
kernel.slub_debug = "options,slabs"
kernel.usbcore.quirks = "0781:5580:bk", "0a5c:5834:gij"
init.splash = ""
init.log_level = "debug"

The kernel commandline is written out as expected:

bash-5.1# cat /proc/cmdline 
crashkernel="2G-:256M" slub_debug="options,slabs" usbcore.quirks="0781:5580:bk" usbcore.quirks="0a5c:5834:gij" console="tty0" console="ttyS1,115200n8" BOOT_IMAGE=(hd0,gpt3)/vmlinuz console=tty0 console=ttyS0,115200n8 net.ifnames=0 netdog.default-interface=eth0:dhcp4,dhcp6? quiet bootconfig root=/dev/dm-0 rootwait ro raid=noautodetect random.trust_cpu=on selinux=1 enforcing=1 dm_verity.max_bios=-1 dm_verity.dev_wait=1 "dm-mod.create=root,,,ro,0 1884160 verity 1 PARTUUID=e00ffc4b-0ffd-4c54-96da-179dcf308bb0/PARTNROFF=1 PARTUUID=e00ffc4b-0ffd-4c54-96da-179dcf308bb0/PARTNROFF=2        4096 4096 235520 1 sha256 5370126d558ff5a2c1b100c3efb1da864dc293e4f314216647743fd96c50e70b 227c3407308c594bb0790cdfa7b322d04ec509ceaa32ace7198c23e285a5817f        2 restart_on_corruption ignore_zero_blocks" -- systemd.log_target=journal-or-kmsg systemd.log_color=0 systemd.show_status=true log_level="debug" splash

Note how on the kernel command line, splash is just written out as splash for the init param.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[stmcginnis]

Great having test coverage!

[zmrow]

🧑‍🔧

Nice work!

[bcressey]

According to the boot config docs:

There can be a key which doesn’t have value or has an empty value. Those keys are used for checking if the key exists or not (like a boolean).

I would expect to have a way to render just splash onto the kernel command line, rather than splash="". Is there a syntax in the boot config format like one of these that would work?

splash =
splash

[etungsten]

splash = is what prompted the linked issue. The kernel apparently is insensitive to whitespace/newlines when parsing the bootconfig from initrd so it grabs the next line as the value for splash. I'm trying out just splash to see if it likes it better.

[etungsten]

Push above changes approach to value-less keys. Prairiedog now differentiates between value-less keys and keys with empty values. Value-less keys are always written out to the bootconfig with just their key.

Updated PR description to include new testing details. I verified the kernel no longer misinterprets value-less keys like splash and treats it as its own bootconfig entry.

[etungsten]

Push above adds to the unit test to show that key = is still parse-able by prairiedog

[mchaker]

Thank you so much for this!