[PATCH doc] Document spectrum-vm

Cole Helbling
2020-06-08T20:45:46Z

spectrum-vm is a handy way to start a crosvm instance for testing crosvm
itself, the kernel, or the rootfs. This commit adds some fledgling
documentation on its functionality and usage.
---
I feel like this is mostly a rough draft, so give me all your
suggestions/criticisms/what have you.

I put this section above the "Hacking on crosvm" section so that it will
be introduced before it is used in an example.

developer-manual.adoc | 43 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 43 insertions(+)

diff --git a/developer-manual.adoc b/developer-manual.adoc
index b7eb2cb..739dc83 100644
--- a/developer-manual.adoc
+++ b/developer-manual.adoc
@@ -106,6 +106,49 @@ the https://spectrum-os.org/doc/crosvm/crosvm/[crosvm documentation]
for the version currently used by Spectrum is hosted on the Spectrum
website.

+==== spectrum-vm
+
+`spectrum-vm` is a shell script that allows for testing various Spectrum
+VM components, including crosvm, the kernel, and the rootfs. The
+simplest way to use this tool is by running `nix-shell -I
+nixpkgs=/path/to/nixpkgs-spectrum -p spectrumPackages.spectrum-vm --run
+spectrum-vm` in a terminal, which will start up an instance of crosvm
+from Nixpkgs running Wayfire in a new window.
+
+****
+Be advised that Wayfire's default keymap is set to Dvorak
+https://spectrum-os.org/git/nixpkgs/tree/pkgs/os-specific/linux/spectrum/rootfs/default.nix[inside
+of the rootfs] -- to change this to your preferred keymap, just set the
+`xkb_layout` option (or remove it altogether for a default of QWERTY).
+****
+
+Once you are ready to end your crosvm session, switch back to where you
+ran `spectrum-vm` and type `reboot` (not `poweroff`). This window is not
+limited to just stopping the VM, however; it is a functional serial
+console and you can even run commands like `env` and `cat
+/etc/passwd`.
+
+As mentioned above, `spectrum-vm` also supports options that allow you
+to specify custom components or run arbitrary commands before exiting:
+
+----
+nix-shell -I nixpkgs=/path/to/nixpkgs-spectrum -p spectrumPackages.spectrum-vm
+
+nix-shell$ spectrum-vm --help
+Usage: spectrum-vm [OPTION]... [-- CROSVM_OPTIONS]
+
+ -c COMMAND shell command to run inside VM
+ -C, --crosvm PATH path to custom crosvm executable
+ -k, --kernel PATH path to custom kernel image
+ -f, --rootfs PATH path to custom root file system image
+ -- CROSVM_OPTIONS extra arguments to pass to crosvm
+
+nix-shell$ spectrum-vm -c 'echo $PATH' # print out the VM's PATH to the serial terminal and exit
+nix-shell$ spectrum-vm -C target/debug/crosvm -- --disable-sandbox # use the specified crosvm and disable sandboxing
+nix-shell$ spectrum-vm -k result/bzImage # use the specified kernel image
+nix-shell$ spectrum-vm -f squashfs # use the specified squashfs as the root filesystem image
+----
+
==== Hacking on crosvm

There are a few ways to get a crosvm development environment. You can
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2.26.2