Re: [Qemu-devel] [PATCH v2 1/2] vfio/mdev: add version attribute for mdev device

[Cornelia Huck]

On Tue, 14 May 2019 02:12:35 -0400
Yan Zhao <address@hidden> wrote:

> On Mon, May 13, 2019 at 09:28:04PM +0800, Erik Skultety wrote:

> > In case of libvirt checking the compatibility, it won't matter how good the
> > error message in the kernel log is and regardless of how many error states 
> > you
> > want to handle, libvirt's only limited to errno here, since we're going to 
> > do
> > plain read/write, so our internal error message returned to the user is only
> > going to contain what the errno says - okay, of course we can (and we DO)
> > provide libvirt specific string, further specifying the error but like I
> > mentioned, depending on how many error cases we want to distinguish this 
> > may be
> > hard for anyone to figure out solely on the error code, as apps will most
> > probably not parse the
> > logs.
> > 
> > Regards,
> > Erik  
> hi Erik
> do you mean you are agreeing on defining common errors and only returning 
> errno?
> 
> e.g.
> #define ENOMIGRATION         140  /* device not supporting migration */
> #define EUNATCH              49  /* software version not match */
> #define EHWNM                142  /* hardware not matching*/

Defining custom error codes is probably not such a good idea... can we
match to common error codes instead? Do we have a good idea about
common error categories, anyway?

(Btw: does libvirt do a generic error-to-description translation, or
does it match to the context? I.e., can libvirt translate well-defined
error codes to a useful message for a specific case?)