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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/04/16 16:02, 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.
>
> Aren't FreeBSD and NetBSD already doing that?

It is not practical for the privcmd driver to do this translation, as
most hypercalls through the privcmd driver are toolstack calls, and have
an unstable layout.

Another thorny issue is that the ioctl() call for privcmd returns errors
via errno, which may be in system errno space, or xen errno space
depending on the source of the errno.

This is very large swamp in desperate need of some attention.

~Andrew

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