muvm-guest: pwbridge: actually read fd indexes in the Transport msg [fix pipewire on x86_64] #204
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I've just gave this a try on Fedora Asahi 43, and I can confirm works fine as-is, without this PR. I think we need to know why is actually switching places... |
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spa_pod_builder_add_struct(b,
SPA_POD_Fd(pw_protocol_native_add_resource_fd(resource, readfd)),
SPA_POD_Fd(pw_protocol_native_add_resource_fd(resource, writefd)),
SPA_POD_Int(mem_id),
SPA_POD_Int(offset),
SPA_POD_Int(size));The order of evaluation of call args in C is unspecified, so it just happens to have the opposite order between targets and/or compilers. The protocol does not rely on it, they can be added in any order, the index is returned and written into the struct. |
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Added actual message parsing now \o/ This should work everywhere. |
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The message payload contains indexes for the attached file descriptors. We must use them instead of relying on the order, which was never guaranteed, and *actually* differs in practice between architectures in compilers because current PipeWire code calls the fd-attaching function inside of function call arguments, which *don't* have a defined evaluation order in the C language standard. Signed-off-by: Val Packett <val@invisiblethingslab.com>
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friendly ping for another (hopefully final) review :) |
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Looks like at some point, PipeWire swapped around the order of the attached fds, so audio playback has been broken here. As a hotfix, follow the change. [..]The message payload contains indexes for the attached file descriptors.
We must use them instead of relying on the order, which was never guaranteed,
and actually differs in practice between architectures in compilers
because current PipeWire code calls the fd-attaching function inside of
function call arguments, which don't have a defined evaluation order
in the C language standard.