Re: [PATCH] 9pfs: Fix some return statements in the synth backend

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Monday, November 28, 2022 11:18:48 AM CET Markus Armbruster wrote:
> Greg Kurz <groug@kaod.org> writes:
> 
> > On Mon, 28 Nov 2022 08:35:22 +0100
> > Markus Armbruster <armbru@redhat.com> wrote:
> >
> >> Greg Kurz <groug@kaod.org> writes:
> >> 
> >> > The qemu_v9fs_synth_mkdir() and qemu_v9fs_synth_add_file() functions
> >> > currently return a positive errno value on failure. This causes
> >> > checkpatch.pl to spit several errors like the one below:
> >> >
> >> > ERROR: return of an errno should typically be -ve (return -EAGAIN)
> >> > #79: FILE: hw/9pfs/9p-synth.c:79:
> >> > +        return EAGAIN;
> >> >
> >> > Simply change the sign. This has no consequence since callers
> >> > assert() the returned value to be equal to 0.
> >> 
> >> Out of curiosity: why is assert() appropriate?
> >> 
> >
> > Most of the code base comes from the original synth backend which
> > was designed to expose QEMU internals to the guest using 9p. The
> > hope of the virtio-9p authors was that each QEMU subsystem would
> > create its own tree using these two functions (note that they
> > are declared extern). Of course these never happened and the synth
> > backend remained nearly dead code for years, until finally it got
> > re-used to implement 9p qtest. In this context, failure to create a
> > synthetic directory or file means the related test has a bug (e.g.
> > messing with the paths used by some other test). This code likely
> > needs improvements but we never got to it.
> 
> I was about to suggest putting this in a file comment, but then I saw
> 
>     /*
>      * Not so fast! You might want to read the 9p developer docs first:
>      * https://wiki.qemu.org/Documentation/9p
>      */
> 
> and behind the link, there's a paragraph "3. synth fs driver".
> 
> Perhaps a brief note on the use of assert() in synth_init() would still
> make sense.  Up to you.

Like what comment would you expect there?

The synth driver is a simplified hack fs driver with hard coded directories &
files, only used for 9p protocol conformance test cases.

Best regards,
Christian Schoenebeck