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. Stefan
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