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

[Luiz Capitulino]

On Wed, 21 Apr 2010 16:15:58 +0100
"Daniel P. Berrange" <address@hidden> wrote:

> 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.

 Fair enough, although mixed languages would be a pain (ie. error desc
in english and this one in something else).

> 
> Regards,
> Daniel