Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 699 insertions, 0 deletions

diff --git a/drivers/video/fbdev/xen-fbfront.c b/drivers/video/fbdev/xen-fbfront.c
new file mode 100644
index 000000000..438597627
--- /dev/null
+++ b/drivers/video/fbdev/xen-fbfront.c
@@ -0,0 +1,699 @@
+/*
+ * Xen para-virtual frame buffer device
+ *
+ * Copyright (C) 2005-2006 Anthony Liguori <aliguori@us.ibm.com>
+ * Copyright (C) 2006-2008 Red Hat, Inc., Markus Armbruster <armbru@redhat.com>
+ *
+ *  Based on linux/drivers/video/q40fb.c
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License. See the file COPYING in the main directory of this archive for
+ *  more details.
+ */
+
+/*
+ * TODO:
+ *
+ * Switch to grant tables when they become capable of dealing with the
+ * frame buffer.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/console.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/fb.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+
+#include <asm/xen/hypervisor.h>
+
+#include <xen/xen.h>
+#include <xen/events.h>
+#include <xen/page.h>
+#include <xen/interface/io/fbif.h>
+#include <xen/interface/io/protocols.h>
+#include <xen/xenbus.h>
+#include <xen/platform_pci.h>
+
+struct xenfb_info {
+	unsigned char		*fb;
+	struct fb_info		*fb_info;
+	int			x1, y1, x2, y2;	/* dirty rectangle,
+						   protected by dirty_lock */
+	spinlock_t		dirty_lock;
+	int			nr_pages;
+	int			irq;
+	struct xenfb_page	*page;
+	unsigned long 		*gfns;
+	int			update_wanted; /* XENFB_TYPE_UPDATE wanted */
+	int			feature_resize; /* XENFB_TYPE_RESIZE ok */
+	struct xenfb_resize	resize;		/* protected by resize_lock */
+	int			resize_dpy;	/* ditto */
+	spinlock_t		resize_lock;
+
+	struct xenbus_device	*xbdev;
+};
+
+#define XENFB_DEFAULT_FB_LEN (XENFB_WIDTH * XENFB_HEIGHT * XENFB_DEPTH / 8)
+
+enum { KPARAM_MEM, KPARAM_WIDTH, KPARAM_HEIGHT, KPARAM_CNT };
+static int video[KPARAM_CNT] = { 2, XENFB_WIDTH, XENFB_HEIGHT };
+module_param_array(video, int, NULL, 0);
+MODULE_PARM_DESC(video,
+	"Video memory size in MB, width, height in pixels (default 2,800,600)");
+
+static void xenfb_make_preferred_console(void);
+static void xenfb_remove(struct xenbus_device *);
+static void xenfb_init_shared_page(struct xenfb_info *, struct fb_info *);
+static int xenfb_connect_backend(struct xenbus_device *, struct xenfb_info *);
+static void xenfb_disconnect_backend(struct xenfb_info *);
+
+static void xenfb_send_event(struct xenfb_info *info,
+			     union xenfb_out_event *event)
+{
+	u32 prod;
+
+	prod = info->page->out_prod;
+	/* caller ensures !xenfb_queue_full() */
+	mb();			/* ensure ring space available */
+	XENFB_OUT_RING_REF(info->page, prod) = *event;
+	wmb();			/* ensure ring contents visible */
+	info->page->out_prod = prod + 1;
+
+	notify_remote_via_irq(info->irq);
+}
+
+static void xenfb_do_update(struct xenfb_info *info,
+			    int x, int y, int w, int h)
+{
+	union xenfb_out_event event;
+
+	memset(&event, 0, sizeof(event));
+	event.type = XENFB_TYPE_UPDATE;
+	event.update.x = x;
+	event.update.y = y;
+	event.update.width = w;
+	event.update.height = h;
+
+	/* caller ensures !xenfb_queue_full() */
+	xenfb_send_event(info, &event);
+}
+
+static void xenfb_do_resize(struct xenfb_info *info)
+{
+	union xenfb_out_event event;
+
+	memset(&event, 0, sizeof(event));
+	event.resize = info->resize;
+
+	/* caller ensures !xenfb_queue_full() */
+	xenfb_send_event(info, &event);
+}
+
+static int xenfb_queue_full(struct xenfb_info *info)
+{
+	u32 cons, prod;
+
+	prod = info->page->out_prod;
+	cons = info->page->out_cons;
+	return prod - cons == XENFB_OUT_RING_LEN;
+}
+
+static void xenfb_handle_resize_dpy(struct xenfb_info *info)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&info->resize_lock, flags);
+	if (info->resize_dpy) {
+		if (!xenfb_queue_full(info)) {
+			info->resize_dpy = 0;
+			xenfb_do_resize(info);
+		}
+	}
+	spin_unlock_irqrestore(&info->resize_lock, flags);
+}
+
+static void xenfb_refresh(struct xenfb_info *info,
+			  int x1, int y1, int w, int h)
+{
+	unsigned long flags;
+	int x2 = x1 + w - 1;
+	int y2 = y1 + h - 1;
+
+	xenfb_handle_resize_dpy(info);
+
+	if (!info->update_wanted)
+		return;
+
+	spin_lock_irqsave(&info->dirty_lock, flags);
+
+	/* Combine with dirty rectangle: */
+	if (info->y1 < y1)
+		y1 = info->y1;
+	if (info->y2 > y2)
+		y2 = info->y2;
+	if (info->x1 < x1)
+		x1 = info->x1;
+	if (info->x2 > x2)
+		x2 = info->x2;
+
+	if (xenfb_queue_full(info)) {
+		/* Can't send right now, stash it in the dirty rectangle */
+		info->x1 = x1;
+		info->x2 = x2;
+		info->y1 = y1;
+		info->y2 = y2;
+		spin_unlock_irqrestore(&info->dirty_lock, flags);
+		return;
+	}
+
+	/* Clear dirty rectangle: */
+	info->x1 = info->y1 = INT_MAX;
+	info->x2 = info->y2 = 0;
+
+	spin_unlock_irqrestore(&info->dirty_lock, flags);
+
+	if (x1 <= x2 && y1 <= y2)
+		xenfb_do_update(info, x1, y1, x2 - x1 + 1, y2 - y1 + 1);
+}
+
+static void xenfb_deferred_io(struct fb_info *fb_info, struct list_head *pagereflist)
+{
+	struct xenfb_info *info = fb_info->par;
+	struct fb_deferred_io_pageref *pageref;
+	unsigned long beg, end;
+	int y1, y2, miny, maxy;
+
+	miny = INT_MAX;
+	maxy = 0;
+	list_for_each_entry(pageref, pagereflist, list) {
+		beg = pageref->offset;
+		end = beg + PAGE_SIZE - 1;
+		y1 = beg / fb_info->fix.line_length;
+		y2 = end / fb_info->fix.line_length;
+		if (y2 >= fb_info->var.yres)
+			y2 = fb_info->var.yres - 1;
+		if (miny > y1)
+			miny = y1;
+		if (maxy < y2)
+			maxy = y2;
+	}
+	xenfb_refresh(info, 0, miny, fb_info->var.xres, maxy - miny + 1);
+}
+
+static struct fb_deferred_io xenfb_defio = {
+	.delay		= HZ / 20,
+	.deferred_io	= xenfb_deferred_io,
+};
+
+static int xenfb_setcolreg(unsigned regno, unsigned red, unsigned green,
+			   unsigned blue, unsigned transp,
+			   struct fb_info *info)
+{
+	u32 v;
+
+	if (regno > info->cmap.len)
+		return 1;
+
+#define CNVT_TOHW(val, width) ((((val)<<(width))+0x7FFF-(val))>>16)
+	red = CNVT_TOHW(red, info->var.red.length);
+	green = CNVT_TOHW(green, info->var.green.length);
+	blue = CNVT_TOHW(blue, info->var.blue.length);
+#undef CNVT_TOHW
+
+	v = (red << info->var.red.offset) |
+	    (green << info->var.green.offset) |
+	    (blue << info->var.blue.offset);
+
+	switch (info->var.bits_per_pixel) {
+	case 16:
+	case 24:
+	case 32:
+		((u32 *)info->pseudo_palette)[regno] = v;
+		break;
+	}
+
+	return 0;
+}
+
+static int
+xenfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
+{
+	struct xenfb_info *xenfb_info;
+	int required_mem_len;
+
+	xenfb_info = info->par;
+
+	if (!xenfb_info->feature_resize) {
+		if (var->xres == video[KPARAM_WIDTH] &&
+		    var->yres == video[KPARAM_HEIGHT] &&
+		    var->bits_per_pixel == xenfb_info->page->depth) {
+			return 0;
+		}
+		return -EINVAL;
+	}
+
+	/* Can't resize past initial width and height */
+	if (var->xres > video[KPARAM_WIDTH] || var->yres > video[KPARAM_HEIGHT])
+		return -EINVAL;
+
+	required_mem_len = var->xres * var->yres * xenfb_info->page->depth / 8;
+	if (var->bits_per_pixel == xenfb_info->page->depth &&
+	    var->xres <= info->fix.line_length / (XENFB_DEPTH / 8) &&
+	    required_mem_len <= info->fix.smem_len) {
+		var->xres_virtual = var->xres;
+		var->yres_virtual = var->yres;
+		return 0;
+	}
+	return -EINVAL;
+}
+
+static int xenfb_set_par(struct fb_info *info)
+{
+	struct xenfb_info *xenfb_info;
+	unsigned long flags;
+
+	xenfb_info = info->par;
+
+	spin_lock_irqsave(&xenfb_info->resize_lock, flags);
+	xenfb_info->resize.type = XENFB_TYPE_RESIZE;
+	xenfb_info->resize.width = info->var.xres;
+	xenfb_info->resize.height = info->var.yres;
+	xenfb_info->resize.stride = info->fix.line_length;
+	xenfb_info->resize.depth = info->var.bits_per_pixel;
+	xenfb_info->resize.offset = 0;
+	xenfb_info->resize_dpy = 1;
+	spin_unlock_irqrestore(&xenfb_info->resize_lock, flags);
+	return 0;
+}
+
+static void xenfb_defio_damage_range(struct fb_info *info, off_t off, size_t len)
+{
+	struct xenfb_info *xenfb_info = info->par;
+
+	xenfb_refresh(xenfb_info, 0, 0, xenfb_info->page->width, xenfb_info->page->height);
+}
+
+static void xenfb_defio_damage_area(struct fb_info *info, u32 x, u32 y,
+				    u32 width, u32 height)
+{
+	struct xenfb_info *xenfb_info = info->par;
+
+	xenfb_refresh(xenfb_info, x, y, width, height);
+}
+
+FB_GEN_DEFAULT_DEFERRED_SYSMEM_OPS(xenfb,
+				   xenfb_defio_damage_range,
+				   xenfb_defio_damage_area)
+
+static const struct fb_ops xenfb_fb_ops = {
+	.owner		= THIS_MODULE,
+	FB_DEFAULT_DEFERRED_OPS(xenfb),
+	.fb_setcolreg	= xenfb_setcolreg,
+	.fb_check_var	= xenfb_check_var,
+	.fb_set_par     = xenfb_set_par,
+};
+
+static irqreturn_t xenfb_event_handler(int rq, void *dev_id)
+{
+	/*
+	 * No in events recognized, simply ignore them all.
+	 * If you need to recognize some, see xen-kbdfront's
+	 * input_handler() for how to do that.
+	 */
+	struct xenfb_info *info = dev_id;
+	struct xenfb_page *page = info->page;
+
+	if (page->in_cons != page->in_prod) {
+		info->page->in_cons = info->page->in_prod;
+		notify_remote_via_irq(info->irq);
+	}
+
+	/* Flush dirty rectangle: */
+	xenfb_refresh(info, INT_MAX, INT_MAX, -INT_MAX, -INT_MAX);
+
+	return IRQ_HANDLED;
+}
+
+static int xenfb_probe(struct xenbus_device *dev,
+		       const struct xenbus_device_id *id)
+{
+	struct xenfb_info *info;
+	struct fb_info *fb_info;
+	int fb_size;
+	int val;
+	int ret = 0;
+
+	info = kzalloc_obj(*info);
+	if (info == NULL) {
+		xenbus_dev_fatal(dev, -ENOMEM, "allocating info structure");
+		return -ENOMEM;
+	}
+
+	/* Limit kernel param videoram amount to what is in xenstore */
+	if (xenbus_scanf(XBT_NIL, dev->otherend, "videoram", "%d", &val) == 1) {
+		if (val < video[KPARAM_MEM])
+			video[KPARAM_MEM] = val;
+	}
+
+	video[KPARAM_WIDTH] = xenbus_read_unsigned(dev->otherend, "width",
+						   video[KPARAM_WIDTH]);
+	video[KPARAM_HEIGHT] = xenbus_read_unsigned(dev->otherend, "height",
+						    video[KPARAM_HEIGHT]);
+
+	/* If requested res does not fit in available memory, use default */
+	fb_size = video[KPARAM_MEM] * 1024 * 1024;
+	if (video[KPARAM_WIDTH] * video[KPARAM_HEIGHT] * XENFB_DEPTH / 8
+	    > fb_size) {
+		pr_warn("display parameters %d,%d,%d invalid, use defaults\n",
+			video[KPARAM_MEM], video[KPARAM_WIDTH],
+			video[KPARAM_HEIGHT]);
+		video[KPARAM_WIDTH] = XENFB_WIDTH;
+		video[KPARAM_HEIGHT] = XENFB_HEIGHT;
+		fb_size = XENFB_DEFAULT_FB_LEN;
+	}
+
+	dev_set_drvdata(&dev->dev, info);
+	info->xbdev = dev;
+	info->irq = -1;
+	info->x1 = info->y1 = INT_MAX;
+	spin_lock_init(&info->dirty_lock);
+	spin_lock_init(&info->resize_lock);
+
+	info->fb = vzalloc(fb_size);
+	if (info->fb == NULL)
+		goto error_nomem;
+
+	info->nr_pages = (fb_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+
+	info->gfns = vmalloc_array(info->nr_pages, sizeof(unsigned long));
+	if (!info->gfns)
+		goto error_nomem;
+
+	/* set up shared page */
+	info->page = (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
+	if (!info->page)
+		goto error_nomem;
+
+	/* abusing framebuffer_alloc() to allocate pseudo_palette */
+	fb_info = framebuffer_alloc(sizeof(u32) * 256, NULL);
+	if (fb_info == NULL)
+		goto error_nomem;
+
+	/* complete the abuse: */
+	fb_info->pseudo_palette = fb_info->par;
+	fb_info->par = info;
+	fb_info->device = &dev->dev;
+
+	fb_info->screen_buffer = info->fb;
+
+	fb_info->fbops = &xenfb_fb_ops;
+	fb_info->var.xres_virtual = fb_info->var.xres = video[KPARAM_WIDTH];
+	fb_info->var.yres_virtual = fb_info->var.yres = video[KPARAM_HEIGHT];
+	fb_info->var.bits_per_pixel = XENFB_DEPTH;
+
+	fb_info->var.red = (struct fb_bitfield){16, 8, 0};
+	fb_info->var.green = (struct fb_bitfield){8, 8, 0};
+	fb_info->var.blue = (struct fb_bitfield){0, 8, 0};
+
+	fb_info->var.activate = FB_ACTIVATE_NOW;
+	fb_info->var.height = -1;
+	fb_info->var.width = -1;
+	fb_info->var.vmode = FB_VMODE_NONINTERLACED;
+
+	fb_info->fix.visual = FB_VISUAL_TRUECOLOR;
+	fb_info->fix.line_length = fb_info->var.xres * XENFB_DEPTH / 8;
+	fb_info->fix.smem_start = 0;
+	fb_info->fix.smem_len = fb_size;
+	strcpy(fb_info->fix.id, "xen");
+	fb_info->fix.type = FB_TYPE_PACKED_PIXELS;
+	fb_info->fix.accel = FB_ACCEL_NONE;
+
+	fb_info->flags = FBINFO_VIRTFB;
+
+	ret = fb_alloc_cmap(&fb_info->cmap, 256, 0);
+	if (ret < 0) {
+		framebuffer_release(fb_info);
+		xenbus_dev_fatal(dev, ret, "fb_alloc_cmap");
+		goto error;
+	}
+
+	fb_info->fbdefio = &xenfb_defio;
+	fb_deferred_io_init(fb_info);
+
+	xenfb_init_shared_page(info, fb_info);
+
+	ret = xenfb_connect_backend(dev, info);
+	if (ret < 0) {
+		xenbus_dev_fatal(dev, ret, "xenfb_connect_backend");
+		goto error_fb;
+	}
+
+	ret = register_framebuffer(fb_info);
+	if (ret) {
+		xenbus_dev_fatal(dev, ret, "register_framebuffer");
+		goto error_fb;
+	}
+	info->fb_info = fb_info;
+
+	xenfb_make_preferred_console();
+	return 0;
+
+error_fb:
+	fb_deferred_io_cleanup(fb_info);
+	fb_dealloc_cmap(&fb_info->cmap);
+	framebuffer_release(fb_info);
+error_nomem:
+	if (!ret) {
+		ret = -ENOMEM;
+		xenbus_dev_fatal(dev, ret, "allocating device memory");
+	}
+error:
+	xenfb_remove(dev);
+	return ret;
+}
+
+static void xenfb_make_preferred_console(void)
+{
+	struct console *c;
+
+	if (console_set_on_cmdline)
+		return;
+
+	console_list_lock();
+	for_each_console(c) {
+		if (!strcmp(c->name, "tty") && c->index == 0)
+			break;
+	}
+	if (c)
+		console_force_preferred_locked(c);
+	console_list_unlock();
+}
+
+static int xenfb_resume(struct xenbus_device *dev)
+{
+	struct xenfb_info *info = dev_get_drvdata(&dev->dev);
+
+	xenfb_disconnect_backend(info);
+	xenfb_init_shared_page(info, info->fb_info);
+	return xenfb_connect_backend(dev, info);
+}
+
+static void xenfb_remove(struct xenbus_device *dev)
+{
+	struct xenfb_info *info = dev_get_drvdata(&dev->dev);
+
+	xenfb_disconnect_backend(info);
+	if (info->fb_info) {
+		fb_deferred_io_cleanup(info->fb_info);
+		unregister_framebuffer(info->fb_info);
+		fb_dealloc_cmap(&info->fb_info->cmap);
+		framebuffer_release(info->fb_info);
+	}
+	free_page((unsigned long)info->page);
+	vfree(info->gfns);
+	vfree(info->fb);
+	kfree(info);
+}
+
+static unsigned long vmalloc_to_gfn(void *address)
+{
+	return xen_page_to_gfn(vmalloc_to_page(address));
+}
+
+static void xenfb_init_shared_page(struct xenfb_info *info,
+				   struct fb_info *fb_info)
+{
+	int i;
+	int epd = PAGE_SIZE / sizeof(info->gfns[0]);
+
+	for (i = 0; i < info->nr_pages; i++)
+		info->gfns[i] = vmalloc_to_gfn(info->fb + i * PAGE_SIZE);
+
+	for (i = 0; i * epd < info->nr_pages; i++)
+		info->page->pd[i] = vmalloc_to_gfn(&info->gfns[i * epd]);
+
+	info->page->width = fb_info->var.xres;
+	info->page->height = fb_info->var.yres;
+	info->page->depth = fb_info->var.bits_per_pixel;
+	info->page->line_length = fb_info->fix.line_length;
+	info->page->mem_length = fb_info->fix.smem_len;
+	info->page->in_cons = info->page->in_prod = 0;
+	info->page->out_cons = info->page->out_prod = 0;
+}
+
+static int xenfb_connect_backend(struct xenbus_device *dev,
+				 struct xenfb_info *info)
+{
+	int ret, evtchn, irq;
+	struct xenbus_transaction xbt;
+
+	ret = xenbus_alloc_evtchn(dev, &evtchn);
+	if (ret)
+		return ret;
+	irq = bind_evtchn_to_irqhandler(evtchn, xenfb_event_handler,
+					0, dev->devicetype, info);
+	if (irq < 0) {
+		xenbus_free_evtchn(dev, evtchn);
+		xenbus_dev_fatal(dev, ret, "bind_evtchn_to_irqhandler");
+		return irq;
+	}
+ again:
+	ret = xenbus_transaction_start(&xbt);
+	if (ret) {
+		xenbus_dev_fatal(dev, ret, "starting transaction");
+		goto unbind_irq;
+	}
+	ret = xenbus_printf(xbt, dev->nodename, "page-ref", "%lu",
+			    virt_to_gfn(info->page));
+	if (ret)
+		goto error_xenbus;
+	ret = xenbus_printf(xbt, dev->nodename, "event-channel", "%u",
+			    evtchn);
+	if (ret)
+		goto error_xenbus;
+	ret = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
+			    XEN_IO_PROTO_ABI_NATIVE);
+	if (ret)
+		goto error_xenbus;
+	ret = xenbus_printf(xbt, dev->nodename, "feature-update", "1");
+	if (ret)
+		goto error_xenbus;
+	ret = xenbus_transaction_end(xbt, 0);
+	if (ret) {
+		if (ret == -EAGAIN)
+			goto again;
+		xenbus_dev_fatal(dev, ret, "completing transaction");
+		goto unbind_irq;
+	}
+
+	xenbus_switch_state(dev, XenbusStateInitialised);
+	info->irq = irq;
+	return 0;
+
+ error_xenbus:
+	xenbus_transaction_end(xbt, 1);
+	xenbus_dev_fatal(dev, ret, "writing xenstore");
+ unbind_irq:
+	unbind_from_irqhandler(irq, info);
+	return ret;
+}
+
+static void xenfb_disconnect_backend(struct xenfb_info *info)
+{
+	/* Prevent xenfb refresh */
+	info->update_wanted = 0;
+	if (info->irq >= 0)
+		unbind_from_irqhandler(info->irq, info);
+	info->irq = -1;
+}
+
+static void xenfb_backend_changed(struct xenbus_device *dev,
+				  enum xenbus_state backend_state)
+{
+	struct xenfb_info *info = dev_get_drvdata(&dev->dev);
+
+	switch (backend_state) {
+	case XenbusStateInitialising:
+	case XenbusStateInitialised:
+	case XenbusStateReconfiguring:
+	case XenbusStateReconfigured:
+	case XenbusStateUnknown:
+		break;
+
+	case XenbusStateInitWait:
+		xenbus_switch_state(dev, XenbusStateConnected);
+		break;
+
+	case XenbusStateConnected:
+		/*
+		 * Work around xenbus race condition: If backend goes
+		 * through InitWait to Connected fast enough, we can
+		 * get Connected twice here.
+		 */
+		if (dev->state != XenbusStateConnected)
+			/* no InitWait seen yet, fudge it */
+			xenbus_switch_state(dev, XenbusStateConnected);
+
+		if (xenbus_read_unsigned(info->xbdev->otherend,
+					 "request-update", 0))
+			info->update_wanted = 1;
+
+		info->feature_resize = xenbus_read_unsigned(dev->otherend,
+							"feature-resize", 0);
+		break;
+
+	case XenbusStateClosed:
+		if (dev->state == XenbusStateClosed)
+			break;
+		fallthrough;	/* Missed the backend's CLOSING state */
+	case XenbusStateClosing:
+		xenbus_frontend_closed(dev);
+		break;
+	}
+}
+
+static const struct xenbus_device_id xenfb_ids[] = {
+	{ "vfb" },
+	{ "" }
+};
+
+static struct xenbus_driver xenfb_driver = {
+	.ids = xenfb_ids,
+	.probe = xenfb_probe,
+	.remove = xenfb_remove,
+	.resume = xenfb_resume,
+	.otherend_changed = xenfb_backend_changed,
+	.not_essential = true,
+};
+
+static int __init xenfb_init(void)
+{
+	if (!xen_domain())
+		return -ENODEV;
+
+	/* Nothing to do if running in dom0. */
+	if (xen_initial_domain())
+		return -ENODEV;
+
+	if (!xen_has_pv_devices())
+		return -ENODEV;
+
+	return xenbus_register_frontend(&xenfb_driver);
+}
+
+static void __exit xenfb_cleanup(void)
+{
+	xenbus_unregister_driver(&xenfb_driver);
+}
+
+module_init(xenfb_init);
+module_exit(xenfb_cleanup);
+
+MODULE_DESCRIPTION("Xen virtual framebuffer device frontend");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("xen:vfb");