Re: [Qemu-devel] [PATCH 3/3] qga: set file descriptor in qmp_guest_file_open non-blocking on Win32

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Denis V. Lunev (2015-10-27 14:13:57)
> On 10/27/2015 10:11 PM, Michael Roth wrote:
> > Quoting Denis V. Lunev (2015-10-27 12:48:43)
> >> From: Olga Krishtal <okrishtal@parallels.com>
> >>
> >> Set fd non-blocking to avoid common use cases (like reading from a
> >> named pipe) from hanging the agent. This was missed in the original
> >> code.
> >>
> >> The patch introduces analog of qemu_set_non/block for HANDLES.
> >> The usage of handles in qemu_set_non/block is impossible, because for
> >> win32 there is a difference between file discriptors and file handles,
> >> and all file ops are made via Win32 api.
> > If this is specific to HANDLEs, why do we need to cast back and forth
> > between int64_t and HANDLE? I haven't build tested, but it seems like
> > this would break for 32-bit mingw builds.
> >
> > I would define these as qemu_set_*_by_handle(HANDLE fh, ...) instead
> > and make them win32 only. If someone wants to introduce a FILE*
> > variant for posix they can introduce it as
> > qemu_set_*_by_handle(FILE *fh, ...) rather than us needing to
> > abstract away the handle type.
> 
> may be it would be better to add static function for this in QGA for now?

I'd be fine with either approach. It could be generally useful for
other w32 users. But if we're thinking about dropping the QGA
use case soon then maybe having it live in QGA is best.

> 
> I am eager to drop this code at once for Posix and Windows and
> switch to GLIB like was done for guest exec.

You mean switching all the guest-file-* interfaces to glib? I
took a stab at it once for w32 guest-file-* implementation, but
one issue I hit was that I couldn't figure out how to implement
guest-file-seek to report back the absolute position in the
file, or whether or not we'd hit EOF. You can set position
via g_io_channel_seek_position(), but if they hit EOF, or are
using relative offsets via G_SEEK_CUR, you don't really know
the position and glib doesn't seem to provide a way to query
that. We could maybe work around it by tracking it manually
via guest-file-* calls but that sounds terrible.

Hopefully I just missed something though. Also couldn't figure
out how you can get glib to report that you'd already seeked
to EOF. I had some comments about it in my WIP:

https://github.com/mdroth/qemu/commit/8b2e5c69266bb48e492af9826122c2aaa4a82197#diff-7f29c3e51a7b387cc7717e7be4f6e205R525

> 
> Den
>