virtio-bindings: check in generated bindings again

This reverts 2c21f25 ("virtio-bindings: use bindgen library from
build.rs"), and goes back to including generated bindings in the repo,
because users have found the requirement to have an up to date
libclang at build time to be onerous.  We started generating the
bindings at build time because we discovered they vary per
architecture, so I've added a new generate-bindings.sh script that
will generate bindings for a list of architectures, which will be easy
to change in future.

Fortunately endianness doesn't seem to make a difference to the
generated bindings.

Signed-off-by: Alyssa Ross <[email protected]>
Fixes: #347

Author: alyssais

virtio-bindings/CHANGELOG.md

@@ -1,5 +1,10 @@
 # Upcoming Release
 
+## Changed
+
+- Bindings are now once again distributed with the crate, rather than
+  generated at build time.
+
 # v0.2.5
 
 ## Changed

virtio-bindings/CONTRIBUTING.md

@@ -1,47 +1,28 @@
 # Contributing to virtio-bindings
 
-## Overview
+## Dependencies
 
-virtio-bindings is periodically updated with imported virtio headers from the
-Linux kernel. The Linux header files have kernel header dependencies that are
-removed during import so that bindgen can process them in isolation without a
-full set of kernel headers. This is also necessary because the licenses of
-individual kernel header files varies and we only want to distribute
-BSD-licensed virtio headers.
+### Bindgen
+The bindings are currently generated using
+[bindgen](https://rust-lang.github.io/rust-bindgen/) version 0.71.1:
+```bash
+cargo install bindgen-cli --vers 0.71.1
+```
 
-## Importing kernel headers
+### Linux Kernel
 Generating bindings depends on the Linux kernel, so you need to have the
 repository on your machine:
 
 ```bash
 git clone https://github.com/torvalds/linux.git
 ```
 
-Install the headers so they can be used for import:
-```bash
-cd linux
-git checkout <linux-version>
-make headers_install INSTALL_HDR_PATH=headers-<linux-version>
-```
+## Example for updating to a new kernel version
 
-Import kernel headers into `include/`:
-```bash
-cd ~/vm-virtio/virtio-bindings
-./import-linux-headers.sh path/to/headers-<linux-version>
-```
+For this example we assume that you have both linux and virtio-bindings
+repositories in your home directory.
 
-Test that the build still works:
 ```bash
-cargo build
+cd ~/vm-virtio/virtio-bindings
+scripts/generate-bindings.sh ~/linux
 ```
-
-## Adding bindings for new header files
-New kernel headers can be added as follows:
-1. Add the new file to import-linux-headers.sh so it is imported from the Linux
-   kernel header directory into include/.
-2. Add the new file to build.rs so bindgen generates bindings.
-3. Add the new module to src/lib.rs so the generated bindings are exposed in
-   the crate.
-4. Check if `cargo build` still succeeds. If the header has new kernel header
-   dependencies then you need to add them (if they are BSD licensed) or stub
-   them out (if they are not BSD licensed).