Re: [Xen-devel] [PATCH for-4.7 3/4] tools/xsplice: fix mixing system errno values with Xen ones.

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Apr 29, 2016 at 05:12:51PM +0200, Roger Pau Monne wrote:
> On Fri, Apr 29, 2016 at 04:02:33PM +0100, Wei Liu wrote:
> > On Fri, Apr 29, 2016 at 04:21:19PM +0200, Roger Pau Monne wrote:
> > > Avoid using system errno values when comparing with Xen errno values.
> > > 
> > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > ---
> > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> > > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > ---
> > > Using errno values inside of hypercall structs is not right IMHO, but 
> > > there
> > > are already several occurrences of this. Although I'm adding the correct 
> > > XEN_
> > > prefixes here, it's very likely that new additions/modifications to this
> > > file will not take this into account, breaking it for OSes != Linux.
> > 
> > This seems to be a rather thorny issue.
> > 
> > I have a gut feeling that returning XEN_ errno to userspace program is
> > layering violation. They should always be translated to OS level errno
> > by privcmd driver.
> 
> Yes, the error value returned from the hypercall executed is indeed 
> translated into the native OS error space. The problem here is that those 
> error codes are returned _inside_ of the specific hypercall struct, which 
> sadly privcmd doesn't know anything about.
> 
> And of course teaching privcmd about every possible hypercall struct is 
> simply impossible, since some of them are not stable (eg: domctls)
>  
> > Aren't FreeBSD and NetBSD already doing that?
> 
> As said above, this is only done for direct return codes, everything inside 
> of the struct passed to the hypercall is returned as-is.
> 
> This is a complete mess, and TBH, I don't have a clever idea about how to 
> solve it.
> 

Me neither. Maybe a new thread should be started to discuss this.

Wei.

> Roger.

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