xdrgen: Prevent reordering of encoder and decoder functions

I noticed that "xdrgen source" reorders the procedure encoder and
decoder functions every time it is run. I would prefer that the
generate

xdrgen: Prevent reordering of encoder and decoder functions

I noticed that "xdrgen source" reorders the procedure encoder and
decoder functions every time it is run. I would prefer that the
generated code be more deterministic: it enables a reader to better
see exactly what has changed between runs of the tool.

The problem is that Python sets are not ordered. I use a Python set
to ensure that, when multiple procedures use a particular argument or
result type, the encoder/decoder for that type is emitted only once.

Sets aren't ordered, but I can use Python dictionaries for this
purpose to ensure the procedure functions are always emitted in the
same order if the .x file does not change.

Signed-off-by: Chuck Lever <[email protected]>

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tools: Add xdrgen

Add a Python-based tool for translating XDR specifications into XDR
encoder and decoder functions written in the Linux kernel's C coding
style. The generator attempts to match the

tools: Add xdrgen

Add a Python-based tool for translating XDR specifications into XDR
encoder and decoder functions written in the Linux kernel's C coding
style. The generator attempts to match the usual C coding style of
the Linux kernel's SunRPC consumers.

This approach is similar to the netlink code generator in
tools/net/ynl .

The maintainability benefits of machine-generated XDR code include:

- Stronger type checking
- Reduces the number of bugs introduced by human error
- Makes the XDR code easier to audit and analyze
- Enables rapid prototyping of new RPC-based protocols
- Hardens the layering between protocol logic and marshaling
- Makes it easier to add observability on demand
- Unit tests might be built for both the tool and (automatically)
for the generated code

In addition, converting the XDR layer to use memory-safe languages
such as Rust will be easier if much of the code can be converted
automatically.

Tested-by: Jeff Layton <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>

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