Update documentation
- Add usage output to provide better idea of cos-kernel-devenv
capabilities
- Make it more clear that cos_kmake should be used in the source tree dir
Change-Id: I96a160f5d60da47cb71a57dd2cc0e6fecb5ef37f
Reviewed-on: https://cos-review.googlesource.com/c/cos/tools/+/25242
Cloud-Build: GCB Service account <228075978874@cloudbuild.gserviceaccount.com>
Reviewed-by: Meena Shanmugam <meenashanmugam@google.com>
Tested-by: Oleksandr Tymoshenko <ovt@google.com>
diff --git a/src/cmd/cos_kernel_devenv/README.md b/src/cmd/cos_kernel_devenv/README.md
index ad4379e..6e804a3 100644
--- a/src/cmd/cos_kernel_devenv/README.md
+++ b/src/cmd/cos_kernel_devenv/README.md
@@ -84,10 +84,53 @@
```
At this point you should be able to run `cos_kmake -h` and get a list of
-available command-line options.
+available command-line options:
+
+```
+Usage: /devenv.sh [-k | -m | -i] [-Hcd] [-A <x86|arm64>] [-C <kernelconfig>]
+ [-B <build> -b <board> | -R <release> | -G <bucket>]
+ [-t <toolchain_version>] [VAR=value ...] [target ...]
+
+Options:
+ -A <arch> target architecture. Valid values are x86 and arm64.
+ -B <build> seed the toolchain from the COS build <build>.
+ Example: R93-16623.0.0 Requires -b option.
+ -C <config> kernel config target. Example: lakitu_defconfig
+ -G <bucket> seed the toolchain and kernel headers from the custom
+ GCS bucket <bucket>. Directory structure needs to conform
+ to the COS standard.
+ -H create a package with kernel headers for the respective
+ kernel package. Should be used only with -k option.
+ -R <release> seed the toolchain and kernel headers from the
+ specified official COS release. Example: 16442.0.0
+ -b <board> specify board for -B argument. Example: lakitu
+ -c perform mrproper step when building a kernel package.
+ Should be used only with -k option.
+ -d create a pakcage with debug symbols for the respective
+ kernel package. Should be used only with -k option.
+ -h show this message.
+ -i invoke interactive shell with kernel development
+ environment initialized.
+ -k build a kernel package for sources mapped from the host
+ to the current working directory.
+ -m build an out-of-tree module for sources mapped from
+ the host to the current working directory.
+ This mode requires either -R or -B/b options.
+ -t seed the toolchain from the Chromium OS upstream.
+ Example: 2021.06.26.094653
+```
### Building the COS Kernel
+#### Getting the Source Code
+
+`cos_kmake` should be used at the top-level of the checked out kernel source tree:
+
+```
+$ git clone -b cos-5.10 https://cos.googlesource.com/third_party/kernel cos-kernel
+$ cd cos-kernel
+```
+
#### Pass-through make
Unless one of `-i`, `-k` or `-m` command-line switches is specified the container
