Re: [PATCH 08/10] hw/9pfs: Allow using hw/9pfs with emscripten

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Saturday, April 12, 2025 12:21:47 PM CEST Christian Schoenebeck wrote:
> On Saturday, April 12, 2025 10:21:47 AM CEST Christian Schoenebeck wrote:
> > On Friday, April 11, 2025 12:47:29 PM CEST Kohei Tokunaga wrote:
[...]
> Let my answer my own question: I just checked the wasi sources. The errno
> values are hard coded by the wasi API, consistent over systems. So the current
> mapping of this patch is wrong. macOS uses a different mapping than the wasi
> API.
> 
> https://github.com/WebAssembly/wasi-libc/blob/main/libc-bottom-half/headers/public/__errno_values.h
> 
> https://github.com/emscripten-core/emscripten/blob/4af36cf80647f9a82be617a0ff32f3e56f220e41/system/include/wasi/api.h#L116
> 
> So please use a correct mapping as defined in that header file.
> 
> /Christian
> 
> > Alternatively 9p2000.u protocol variant could be used for Emscripten. Not
> > ideal, as this 9p protocol version is somewhat a legacy protocol from QEMU
> > perspective, reduced performance, less reliable, but it transmits error
> > strings to client which it can map to correct errno values by itself. Linux 9p
> > client uses a hash map for this errno translation of 9p2000.u error strings.

Stupid me. That's host errno -> Linux errno translation. So your values are
obviously correct, sorry!

However still worth comparing the Linux vs. wasi header files on this.

And I would avoid duplicating the macOS translation code. Instead I would just
do a one-line change:

#elif defined(CONFIG_DARWIN) || defined(EMSCRIPTEN)
...

And probably leave a comment with a link to the wasi API header file there, so
in case new errno translations are added for macOS, that people also check
whether those macros exist in the wasi header file as well.

/Christian