Re: [Qemu-devel] KVM call minutes for Feb 15

[Avi Kivity]

On 02/17/2011 03:10 PM, Anthony Liguori wrote:
> On 02/17/2011 06:23 AM, Avi Kivity wrote:
> > On 02/17/2011 02:12 PM, Anthony Liguori wrote:
> > > > (btw what happens in a non-UTF-8 locale? I guess we should just 
> > > > reject unencodable strings).
> > >
> > >
> > > While QEMU is mostly ASCII internally, for the purposes of the JSON 
> > > parser, we always encode and decode UTF-8.  We reject invalid UTF-8 
> > > sequences.  But since JSON is string-encoded unicode, we can always 
> > > decode a JSON string to valid UTF-8 as long as the string is well 
> > > formed.
> >
> > That is wrong.  If the user passes a Unicode filename it is expected 
> > to be translated to the current locale encoding for the purpose of, 
> > say, filename lookup.
>
> QEMU does not support anything but UTF-8.

Since when?

AFAICT, JSON string conversion is the only place where there is any 
dependency on UTF-8.  Anything else should just work.

> That's pretty common with Unix software.  I don't think any modern 
> Unix platform actually uses UCS2 or UTF-16.  It's either ascii or UTF-8.

Most/all Linux distributions support UTF-8 as well as a zillion other 
encodings (single-byte ASCII + another charset, or multi-byte charsets 
for languages with many characters.

> The only place it even matters is Windows and Windows has ASCII and 
> UTF-16 versions of their APIs.  So on Windows, non-ASCII characters 
> won't be handled correctly (yet another one of the many issues with 
> Windows support in QEMU).  UTF-8 is self-recovering though so it 
> degrades gracefully.

It matters on Linux with el_GR.iso88597, for example.  If you feed a 
JSON string and translate it blindly to UTF-8, you'll get garbage when 
you feed it to system calls.

Practically everyone uses UTF-8 these days, so the impact is minimal, 
but it is more correct (as well as simpler) to ask the system libraries 
to encode using the current locale.

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