Re: [Qemu-devel] [PATCH 07/22] qemu-error: Introduce get_errno_string()

[Daniel P. Berrange]

On Wed, Apr 21, 2010 at 12:12:14PM -0300, Luiz Capitulino wrote:
> On Wed, 21 Apr 2010 18:42:38 +0400 (MSD)
> malc <address@hidden> wrote:
> 
> > On Wed, 21 Apr 2010, Kevin Wolf wrote:
> > 
> > > Am 21.04.2010 10:28, schrieb Daniel P. Berrange:
> > > > On Tue, Apr 20, 2010 at 06:09:37PM -0300, Luiz Capitulino wrote:
> > > >> There are error handling functions in QEMU which print errno codes
> > > >> to the user. While it's debatable if this is good from a user
> > > >> perspective, sometimes it's the best you can do because it's what
> > > >> system calls return and this is also useful for debugging.
> > > >>
> > > >> So, we need a way to expose those codes in QMP. We can't use the
> > > >> codes themselfs because they may vary between systems.
> > > >>
> > > >> The best solution I can think of is returning the string
> > > >> representation of the name. For example, EIO becomes "EIO".
> > > >>
> > > >> This is what get_errno_string() does.
> > > >>
> > > >> Signed-off-by: Luiz Capitulino <address@hidden>
> > > >> ---
> > > >>  qemu-error.c |   25 +++++++++++++++++++++++++
> > > >>  qemu-error.h |    1 +
> > > >>  2 files changed, 26 insertions(+), 0 deletions(-)
> > > >>
> > > >> diff --git a/qemu-error.c b/qemu-error.c
> > > >> index 5a35e7c..55ce133 100644
> > > >> --- a/qemu-error.c
> > > >> +++ b/qemu-error.c
> > > >> @@ -207,3 +207,28 @@ void error_report(const char *fmt, ...)
> > > >>      va_end(ap);
> > > >>      error_printf("\n");
> > > >>  }
> > > >> +
> > > >> +/*
> > > >> + * This is probably only useful for QMP
> > > >> + */
> > > >> +const char *get_errno_string(int err)
> > > >> +{
> > > >> +    assert(err < 0);
> > > >> +
> > > >> +    switch (err) {
> > > >> +    case -EINVAL:
> > > >> +        return "EINVAL";
> > > >> +    case -EIO:
> > > >> +        return "EIO";
> > > >> +    case -ENOENT:
> > > >> +        return "ENOENT";
> > > >> +    case -ENOMEDIUM:
> > > >> +        return "ENOMEDIUM";
> > > >> +    case -ENOTSUP:
> > > >> +        return "ENOTSUP";
> > > >> +    default:
> > > >> +        return "unknown";
> > > >> +    }
> > > >> +
> > > >> +    abort();
> > > >> +}
> > > > 
> > > > Wouldn't it be nicer to return strerror_r()  output instead of errno
> > > > names ?
> > > 
> > > I agree. And it would be more complete, too.
> > 
> > OTOH it has a problem of returning translated messages (subject to
> > LC_MESSAGES value).
> 
>  Exactly, and I'm not sure if there's anything that ensure they're
> exactly the same among different systems.

I thought QMP already declared that the printable error strings are subject
to arbitrary change at any time, which includes translation? Apps needing 
something reliable should be hooking onto the error code.

Regards,
Daniel
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