From: "Daniel P. Berrange" <berrange@redhat.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Stefan Hajnoczi <stefanha@gmail.com>,
Tony Luck <tony.luck@intel.com>,
Kees Cook <keescook@chromium.org>,
kvm@vger.kernel.org, Radim Kr??m???? <rkrcmar@redhat.com>,
Anton Vorontsov <anton@enomsg.org>,
LKML <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
qemu-devel@nongnu.org, Minchan Kim <minchan@kernel.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
Anthony Liguori <aliguori@amazon.com>,
Colin Cross <ccross@android.com>,
Paolo Bonzini <pbonzini@redhat.com>,
virtualization@lists.linux-foundation.org,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [Qemu-devel] [PATCH 6/7] qemu: Implement virtio-pstore device
Date: Mon, 1 Aug 2016 10:21:30 +0100 [thread overview]
Message-ID: <20160801092130.GE6455@redhat.com> (raw)
In-Reply-To: <20160730083827.GA26275@danjae.aot.lge.com>
On Sat, Jul 30, 2016 at 05:38:27PM +0900, Namhyung Kim wrote:
> Hello,
>
> On Thu, Jul 28, 2016 at 02:08:41PM +0100, Daniel P. Berrange wrote:
> > On Thu, Jul 28, 2016 at 01:56:07PM +0100, Stefan Hajnoczi wrote:
> > > On Thu, Jul 28, 2016 at 02:39:53PM +0900, Namhyung Kim wrote:
> > > > On Thu, Jul 28, 2016 at 03:02:54AM +0300, Michael S. Tsirkin wrote:
> > > > > On Thu, Jul 28, 2016 at 12:08:30AM +0900, Namhyung Kim wrote:
> > > > > > +static ssize_t virtio_pstore_do_write(VirtIOPstore *s, struct iovec *out_sg,
> > > > > > + unsigned int out_num,
> > > > > > + struct virtio_pstore_req *req)
> > > > > > +{
> > > > > > + char path[PATH_MAX];
> > > > > > + int fd;
> > > > > > + ssize_t len;
> > > > > > + unsigned short type;
> > > > > > + int flags = O_WRONLY | O_CREAT;
> > > > > > +
> > > > > > + /* we already consume the req */
> > > > > > + iov_discard_front(&out_sg, &out_num, sizeof(*req));
> > > > > > +
> > > > > > + virtio_pstore_to_filename(s, path, sizeof(path), req);
> > > > > > +
> > > > > > + type = le16_to_cpu(req->type);
> > > > > > +
> > > > > > + if (type == VIRTIO_PSTORE_TYPE_DMESG) {
> > > > > > + flags |= O_TRUNC;
> > > > > > + } else if (type == VIRTIO_PSTORE_TYPE_CONSOLE) {
> > > > > > + flags |= O_APPEND;
> > > > > > + }
> > > > > > +
> > > > > > + fd = open(path, flags, 0644);
> > > > > > + if (fd < 0) {
> > > > > > + error_report("cannot open %s", path);
> > > > > > + return -1;
> > > > > > + }
> > > > > > + len = writev(fd, out_sg, out_num);
> > > > > > + close(fd);
> > > > > > +
> > > > > > + return len;
> > > > >
> > > > > All this is blocking VM until host io completes.
> > > >
> > > > Hmm.. I don't know about the internals of qemu. So does it make guest
> > > > stop? If so, that's what I want to do for _DMESG. :) As it's called
> > > > only on kernel oops I think it's admittable. But for _CONSOLE, it
> > > > needs to do asynchronously. Maybe I can add a thread to do the work.
> > >
> > > Please look at include/io/channel.h. QEMU is event-driven and tends to
> > > use asynchronous I/O instead of spawning threads. The include/io/ APIs
> > > allow you to do asynchronous I/O in the event loop.
> >
> > That is true, except for I/O to/from plain files - the QIOChannelFile
> > impl doesn't do anything special (yet) to make that work correctly in
> > non-blocking mode. Of course that could be fixed...
>
> Yep, I don't know how I can use the QIOChannelFile for async IO.
> AFAICS it's just a wrapper for normal readv/writev. Who is
> responsible to do these IO when I use the IO channel API? Also does
> it guarantee that all IOs are processed in order?
I'd suggest just using QIOChannelFile regardless - we need to fix the
blocking behaviour already for sake of the qemu chardev code, and your
code just adds more pressure to fix it. I/O will be done in the order
in which you make the calls, as with regular POSIX I/O funcs you're
currently using.
Regards,
Daniel
--
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next prev parent reply other threads:[~2016-08-01 9:48 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-27 15:08 [RFC/PATCHSET 0/7] virtio: Implement virtio pstore device (v2) Namhyung Kim
2016-07-27 15:08 ` [PATCH 1/7] pstore: Split pstore fragile flags Namhyung Kim
2016-07-27 15:08 ` [PATCH 2/7] pstore/ram: Set pstore flags dynamically Namhyung Kim
2016-07-27 15:08 ` [PATCH 3/7] pstore: Manage buffer position for async write Namhyung Kim
2016-07-27 15:08 ` [PATCH 4/7] virtio: Basic implementation of virtio pstore driver Namhyung Kim
2016-07-27 15:08 ` [PATCH 5/7] virtio-pstore: Support PSTORE_TYPE_CONSOLE Namhyung Kim
2016-07-27 15:08 ` [PATCH 6/7] qemu: Implement virtio-pstore device Namhyung Kim
2016-07-28 0:02 ` Michael S. Tsirkin
2016-07-28 5:39 ` Namhyung Kim
2016-07-28 12:56 ` Stefan Hajnoczi
2016-07-28 13:08 ` [Qemu-devel] " Daniel P. Berrange
2016-07-30 8:38 ` Namhyung Kim
2016-08-01 9:21 ` Daniel P. Berrange [this message]
2016-08-01 15:34 ` Namhyung Kim
2016-07-28 14:38 ` Steven Rostedt
2016-07-28 13:22 ` [Qemu-devel] " Daniel P. Berrange
2016-07-30 8:57 ` Namhyung Kim
2016-08-01 9:24 ` Daniel P. Berrange
2016-08-01 15:52 ` Namhyung Kim
2016-07-27 15:08 ` [PATCH 7/7] kvmtool: " Namhyung Kim
2016-07-27 22:18 ` [RFC/PATCHSET 0/7] virtio: Implement virtio pstore device (v2) Michael S. Tsirkin
2016-07-28 2:46 ` Namhyung Kim
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