Re: [Qemu-devel] [Qemu-block] [PATCH v1 1/1] block: Add numeric errno field to BLOCK_IO_ERROR events

[Eric Blake]

On 12/21/2017 07:08 PM, Eric Blake wrote:

> >   #
> > +# @errno: int describing the error cause, provided for applications.
> > +#         (Note: while most errnos are posix compliant between OSs, it
> > +#         is possible some errno values can vary among different OSs.)
> > +#         (since 2.12)
>
> The proof is in the pudding - if your documentation has to give this big 
> disclaimer, then what you are adding is not portable and should not be 
> added in that manner.

To follow up to myself, POSIX explicitly says that errno values are 
implementation dependent, and there is NO requirement that errno value 1 
be EPERM, for example.  And while qemu does not target GNU Hurd, that is 
a classic example of a system where errno values intentionally do not 
fit in 8 bits.  So you can't argue that there are "POSIX-compliant errno 
values", because POSIX doesn't mandate specific values.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org