Re: [Xen-devel] [PATCH 02/11] xen/gntdev: allow usermode to mapgranted pages

[Konrad Rzeszutek Wilk]

On Wed, Dec 15, 2010 at 01:40:37PM +0000, stefano.stabellini@xxxxxxxxxxxxx wrote:
> From: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> 
> The gntdev driver allows usermode to map granted pages from other
> domains.  This is typically used to implement a Xen backend driver
> in user mode.

scripts/checkpatch.pl goes haywire on this patch. Any chance you can
make it cleaner? (or perhaps a subsequent patch to fix the checkpatch.pl
isseus?)

The issues are mainly the printk's can be converted to pr_debug..

> 
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> Signed-off-by: Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> ---
>  drivers/xen/Kconfig  |    7 +
>  drivers/xen/Makefile |    2 +
>  drivers/xen/gntdev.c |  646 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/xen/gntdev.h |  119 +++++++++
>  4 files changed, 774 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/xen/gntdev.c
>  create mode 100644 include/xen/gntdev.h
> 
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 6e6180c..0c6d2a1 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -62,6 +62,13 @@ config XEN_SYS_HYPERVISOR
>  	 virtual environment, /sys/hypervisor will still be present,
>  	 but will have no xen contents.
>  
> +config XEN_GNTDEV
> +	tristate "userspace grant access device driver"
> +	depends on XEN
> +	select MMU_NOTIFIER
> +	help
> +	  Allows userspace processes use grants.
				    ^^- "to"

> +	  
>  config XEN_PLATFORM_PCI
>  	tristate "xen platform pci device driver"
>  	depends on XEN_PVHVM
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 533a199..674fdb5 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -9,6 +9,7 @@ obj-$(CONFIG_HOTPLUG_CPU)	+= cpu_hotplug.o
>  obj-$(CONFIG_XEN_XENCOMM)	+= xencomm.o
>  obj-$(CONFIG_XEN_BALLOON)	+= balloon.o
>  obj-$(CONFIG_XEN_DEV_EVTCHN)	+= xen-evtchn.o
> +obj-$(CONFIG_XEN_GNTDEV)	+= xen-gntdev.o
>  obj-$(CONFIG_XENFS)		+= xenfs/
>  obj-$(CONFIG_XEN_SYS_HYPERVISOR)	+= sys-hypervisor.o
>  obj-$(CONFIG_XEN_PLATFORM_PCI)	+= platform-pci.o
> @@ -16,4 +17,5 @@ obj-$(CONFIG_SWIOTLB_XEN)	+= swiotlb-xen.o
>  obj-$(CONFIG_XEN_DOM0)		+= pci.o
>  
>  xen-evtchn-y			:= evtchn.o
> +xen-gntdev-y				:= gntdev.o
>  
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> new file mode 100644
> index 0000000..45898d4
> --- /dev/null
> +++ b/drivers/xen/gntdev.c
> @@ -0,0 +1,646 @@
> +/******************************************************************************
> + * gntdev.c
> + *
> + * Device for accessing (in user-space) pages that have been granted by other
> + * domains.
> + *
> + * Copyright (c) 2006-2007, D G Murray.
> + *           (c) 2009 Gerd Hoffmann <kraxel@xxxxxxxxxx>
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/miscdevice.h>
> +#include <linux/fs.h>
> +#include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/mmu_notifier.h>
> +#include <linux/types.h>
> +#include <linux/uaccess.h>
> +#include <linux/sched.h>
> +#include <linux/spinlock.h>
> +#include <linux/slab.h>
> +
> +#include <xen/xen.h>
> +#include <xen/grant_table.h>
> +#include <xen/gntdev.h>
> +#include <asm/xen/hypervisor.h>
> +#include <asm/xen/hypercall.h>
> +#include <asm/xen/page.h>
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Derek G. Murray <Derek.Murray@xxxxxxxxxxxx>, "
> +	      "Gerd Hoffmann <kraxel@xxxxxxxxxx>");
> +MODULE_DESCRIPTION("User-space granted page access driver");
> +
> +static int debug = 0;
> +module_param(debug, int, 0644);

You need to add:
MODULE_PARM_DESC

> +static int limit = 1024;
> +module_param(limit, int, 0644);

ditto
> +
> +struct gntdev_priv {
> +	struct list_head maps;
> +	uint32_t used;
> +	uint32_t limit;
> +	spinlock_t lock;

and some description about what the lock is protecting.
> +	struct mm_struct *mm;
> +	struct mmu_notifier mn;
> +};
> +
> +struct grant_map {
> +	struct list_head next;
> +	struct gntdev_priv *priv;
> +	struct vm_area_struct *vma;
> +	int index;
> +	int count;
> +	int flags;
> +	int is_mapped;
> +	struct ioctl_gntdev_grant_ref *grants;
> +	struct gnttab_map_grant_ref   *map_ops;
> +	struct gnttab_unmap_grant_ref *unmap_ops;
> +};
> +
> +/* ------------------------------------------------------------------ */
> +
> +static void gntdev_print_maps(struct gntdev_priv *priv,
> +			      char *text, int text_index)
> +{
> +	struct grant_map *map;
> +
> +	printk("%s: maps list (priv %p, usage %d/%d)\n",
> +	       __FUNCTION__, priv, priv->used, priv->limit);
> +	list_for_each_entry(map, &priv->maps, next)
> +		printk("  index %2d, count %2d %s\n",

Use pr_debug.

> +		       map->index, map->count,
> +		       map->index == text_index && text ? text : "");
> +}
> +
> +static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
> +{
> +	struct grant_map *add;
> +
> +	add = kzalloc(sizeof(struct grant_map), GFP_KERNEL);
> +	if (NULL == add)
> +		return NULL;
> +
> +	add->grants    = kzalloc(sizeof(add->grants[0])    * count, GFP_KERNEL);
> +	add->map_ops   = kzalloc(sizeof(add->map_ops[0])   * count, GFP_KERNEL);
> +	add->unmap_ops = kzalloc(sizeof(add->unmap_ops[0]) * count, GFP_KERNEL);
> +	if (NULL == add->grants  ||
> +	    NULL == add->map_ops ||
> +	    NULL == add->unmap_ops)
> +		goto err;
> +
> +	add->index = 0;
> +	add->count = count;
> +	add->priv  = priv;
> +
> +	if (add->count + priv->used > priv->limit)
> +		goto err;
> +
> +	return add;
> +
> +err:
> +	kfree(add->grants);
> +	kfree(add->map_ops);
> +	kfree(add->unmap_ops);
> +	kfree(add);
> +	return NULL;
> +}
> +
> +static void gntdev_add_map(struct gntdev_priv *priv, struct grant_map *add)
> +{
> +	struct grant_map *map;
> +
> +	list_for_each_entry(map, &priv->maps, next) {
> +		if (add->index + add->count < map->index) {
> +			list_add_tail(&add->next, &map->next);
> +			goto done;
> +		}
> +		add->index = map->index + map->count;
> +	}
> +	list_add_tail(&add->next, &priv->maps);
> +
> +done:
> +	priv->used += add->count;
> +	if (debug)
> +		gntdev_print_maps(priv, "[new]", add->index);
> +}
> +
> +static struct grant_map *gntdev_find_map_index(struct gntdev_priv *priv, int index,
> +					       int count)
> +{
> +	struct grant_map *map;
> +
> +	list_for_each_entry(map, &priv->maps, next) {
> +		if (map->index != index)
> +			continue;
> +		if (map->count != count)
> +			continue;
> +		return map;
> +	}
> +	return NULL;
> +}
> +
> +static struct grant_map *gntdev_find_map_vaddr(struct gntdev_priv *priv,
> +					       unsigned long vaddr)
> +{
> +	struct grant_map *map;
> +
> +	list_for_each_entry(map, &priv->maps, next) {
> +		if (!map->vma)
> +			continue;
> +		if (vaddr < map->vma->vm_start)
> +			continue;
> +		if (vaddr >= map->vma->vm_end)
> +			continue;
> +		return map;
> +	}
> +	return NULL;
> +}
> +
> +static int gntdev_del_map(struct grant_map *map)
> +{
> +	int i;
> +
> +	if (map->vma)
> +		return -EBUSY;
> +	for (i = 0; i < map->count; i++)
> +		if (map->unmap_ops[i].handle)
> +			return -EBUSY;
> +
> +	map->priv->used -= map->count;
> +	list_del(&map->next);
> +	return 0;
> +}
> +
> +static void gntdev_free_map(struct grant_map *map)
> +{
> +	if (!map)
> +		return;
> +	kfree(map->grants);
> +	kfree(map->map_ops);
> +	kfree(map->unmap_ops);
> +	kfree(map);
> +}
> +
> +/* ------------------------------------------------------------------ */
> +
> +static int find_grant_ptes(pte_t *pte, pgtable_t token, unsigned long addr, void *data)
> +{
> +	struct grant_map *map = data;
> +	unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT;
> +	u64 pte_maddr;
> +
> +	BUG_ON(pgnr >= map->count);
> +	pte_maddr  = (u64)pfn_to_mfn(page_to_pfn(token)) << PAGE_SHIFT;
> +	pte_maddr += (unsigned long)pte & ~PAGE_MASK;
> +	gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, map->flags,
> +			  map->grants[pgnr].ref,
> +			  map->grants[pgnr].domid);
> +	gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr, map->flags,
> +			    0 /* handle */);
> +	return 0;
> +}
> +
> +static int map_grant_pages(struct grant_map *map)
> +{
> +	int i, err = 0;
> +
> +	if (debug)
> +		printk("%s: map %d+%d\n", __FUNCTION__, map->index, map->count);

pr_debug ought to do it.

> +	err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
> +					map->map_ops, map->count);
> +	if (WARN_ON(err))
> +		return err;
> +
> +	for (i = 0; i < map->count; i++) {
> +		if (map->map_ops[i].status)
> +			err = -EINVAL;

You WARN_ON earlier, but not here
> +		map->unmap_ops[i].handle = map->map_ops[i].handle;
> +	}

or here .. would it make sense to do it?

> +	return err;
> +}
> +
> +static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
> +{
> +	int i, err = 0;
> +
> +	if (debug)
> +		printk("%s: map %d+%d [%d+%d]\n", __FUNCTION__,
> +		       map->index, map->count, offset, pages);

ditto.
> +	err = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
> +					map->unmap_ops + offset, pages);
> +	if (WARN_ON(err))
> +		return err;
> +
> +	for (i = 0; i < pages; i++) {
> +		if (map->unmap_ops[offset+i].status)
> +			err = -EINVAL;
> +		map->unmap_ops[offset+i].handle = 0;
> +	}
> +	return err;
> +}
> +
> +/* ------------------------------------------------------------------ */
> +
> +static void gntdev_vma_close(struct vm_area_struct *vma)
> +{
> +	struct grant_map *map = vma->vm_private_data;
> +
> +	if (debug)
> +		printk("%s\n", __FUNCTION__);
> +	map->is_mapped = 0;
> +	map->vma = NULL;
> +	vma->vm_private_data = NULL;
> +}
> +
> +static int gntdev_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> +	if (debug)
> +		printk("%s: vaddr %p, pgoff %ld (shouldn't happen)\n",
> +		       __FUNCTION__, vmf->virtual_address, vmf->pgoff);
> +	vmf->flags = VM_FAULT_ERROR;
> +	return 0;
> +}
> +
> +static struct vm_operations_struct gntdev_vmops = {
> +	.close = gntdev_vma_close,
> +	.fault = gntdev_vma_fault,
> +};
> +
> +/* ------------------------------------------------------------------ */
> +
> +static void mn_invl_range_start(struct mmu_notifier *mn,
> +				struct mm_struct *mm,
> +				unsigned long start, unsigned long end)
> +{
> +	struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
> +	struct grant_map *map;
> +	unsigned long mstart, mend;
> +	int err;
> +
> +	spin_lock(&priv->lock);
> +	list_for_each_entry(map, &priv->maps, next) {
> +		if (!map->vma)
> +			continue;
> +		if (!map->is_mapped)
> +			continue;
> +		if (map->vma->vm_start >= end)
> +			continue;
> +		if (map->vma->vm_end <= start)
> +			continue;
> +		mstart = max(start, map->vma->vm_start);
> +		mend   = min(end,   map->vma->vm_end);
> +		if (debug)
> +			printk("%s: map %d+%d (%lx %lx), range %lx %lx, mrange %lx %lx\n",
> +			       __FUNCTION__, map->index, map->count,
> +			       map->vma->vm_start, map->vma->vm_end,
> +			       start, end, mstart, mend);
> +		err = unmap_grant_pages(map,
> +					(mstart - map->vma->vm_start) >> PAGE_SHIFT,
> +					(mend - mstart) >> PAGE_SHIFT);
> +		WARN_ON(err);

Ah you WARN here.. so two WARN_ON in case the hypervisor call fails.
Maybe you just remove the WARN_ON in the unmap_grant_pages and let this
WARN_ON do the job?

> +	}
> +	spin_unlock(&priv->lock);
> +}
> +
> +static void mn_invl_page(struct mmu_notifier *mn,
> +			 struct mm_struct *mm,
> +			 unsigned long address)
> +{
> +	mn_invl_range_start(mn, mm, address, address + PAGE_SIZE);
> +}
> +
> +static void mn_release(struct mmu_notifier *mn,
> +		       struct mm_struct *mm)
> +{
> +	struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
> +	struct grant_map *map;
> +	int err;
> +
> +	spin_lock(&priv->lock);
> +	list_for_each_entry(map, &priv->maps, next) {
> +		if (!map->vma)
> +			continue;
> +		if (debug)
> +			printk("%s: map %d+%d (%lx %lx)\n",
> +			       __FUNCTION__, map->index, map->count,
> +			       map->vma->vm_start, map->vma->vm_end);
> +		err = unmap_grant_pages(map, 0, map->count);

Ok, so offset set to zero (might want a put /* offset */ comment in there.

> +		WARN_ON(err);
> +	}
> +	spin_unlock(&priv->lock);
> +}
> +
> +struct mmu_notifier_ops gntdev_mmu_ops = {
> +	.release                = mn_release,
> +	.invalidate_page        = mn_invl_page,
> +	.invalidate_range_start = mn_invl_range_start,
> +};
> +
> +/* ------------------------------------------------------------------ */
> +
> +static int gntdev_open(struct inode *inode, struct file *flip)
> +{
> +	struct gntdev_priv *priv;
> +
> +	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&priv->maps);
> +	spin_lock_init(&priv->lock);
> +	priv->limit = limit;
> +
> +	priv->mm = get_task_mm(current);
> +	if (!priv->mm) {
> +		kfree(priv);
> +		return -ENOMEM;
> +	}
> +	priv->mn.ops = &gntdev_mmu_ops;
> +	mmu_notifier_register(&priv->mn, priv->mm);

You might want to check that this does not fail.

> +	mmput(priv->mm);
> +
> +	flip->private_data = priv;
> +	if (debug)
> +		printk("%s: priv %p\n", __FUNCTION__, priv);
> +
> +	return 0;
> +}
> +
> +static int gntdev_release(struct inode *inode, struct file *flip)
> +{
> +	struct gntdev_priv *priv = flip->private_data;
> +	struct grant_map *map;
> +	int err;
> +
> +	if (debug)
> +		printk("%s: priv %p\n", __FUNCTION__, priv);
> +
> +	spin_lock(&priv->lock);
> +	while (!list_empty(&priv->maps)) {
> +		map = list_entry(priv->maps.next, struct grant_map, next);
> +		err = gntdev_del_map(map);
> +		if (WARN_ON(err))

Hmm, so if we fail (b/c we get -EBUSY) we free it? Would it be possible
to race with whoever is responsible for releasing this VMA  (mn_release)
clearning this map while the holder of this map is trying to dereference
the map->unmap_ops ?

Oh wait, you and mn_release are both using  a spinlock.. so, under what
conditions would this actually happend?

> +			gntdev_free_map(map);
> +
> +	}
> +	spin_unlock(&priv->lock);
> +
> +	mmu_notifier_unregister(&priv->mn, priv->mm);
> +	kfree(priv);
> +	return 0;
> +}
> +
> +static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,

The decleration is for 'long' but you return int. Looking at the
other ioctl (kvm ones) they all seem to return 'int' so this
decleration looks wrong.

> +				       struct ioctl_gntdev_map_grant_ref __user *u)
> +{
> +	struct ioctl_gntdev_map_grant_ref op;
> +	struct grant_map *map;
> +	int err;
> +
> +	if (copy_from_user(&op, u, sizeof(op)) != 0)
> +		return -EFAULT;
> +	if (debug)
> +		printk("%s: priv %p, add %d\n", __FUNCTION__, priv,
> +		       op.count);
> +	if (unlikely(op.count <= 0))
> +		return -EINVAL;
> +	if (unlikely(op.count > priv->limit))
> +		return -EINVAL;
> +
> +	err = -ENOMEM;
> +	map = gntdev_alloc_map(priv, op.count);
> +	if (!map)
> +		return err;
> +	if (copy_from_user(map->grants, &u->refs,
> +			   sizeof(map->grants[0]) * op.count) != 0) {
> +		gntdev_free_map(map);
> +		return err;
> +	}
> +
> +	spin_lock(&priv->lock);
> +	gntdev_add_map(priv, map);
> +	op.index = map->index << PAGE_SHIFT;
> +	spin_unlock(&priv->lock);
> +
> +	if (copy_to_user(u, &op, sizeof(op)) != 0) {
> +		spin_lock(&priv->lock);
> +		gntdev_del_map(map);
> +		spin_unlock(&priv->lock);
> +		gntdev_free_map(map);
> +		return err;
> +	}
> +	return 0;
> +}
> +
> +static long gntdev_ioctl_unmap_grant_ref(struct gntdev_priv *priv,

Same thing. Perhaps 'int' would be better suited.
> +					 struct ioctl_gntdev_unmap_grant_ref __user *u)
> +{
> +	struct ioctl_gntdev_unmap_grant_ref op;
> +	struct grant_map *map;
> +	int err = -EINVAL;

Not -ENOENT? If you can't find the map .. well, the arguments are valid.
It is just that the map is not found. Or are the tools hard-coded to look
for -EINVAL?

> +
> +	if (copy_from_user(&op, u, sizeof(op)) != 0)
> +		return -EFAULT;
> +	if (debug)
> +		printk("%s: priv %p, del %d+%d\n", __FUNCTION__, priv,
> +		       (int)op.index, (int)op.count);
> +
> +	spin_lock(&priv->lock);
> +	map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
> +	if (map)
> +		err = gntdev_del_map(map);
> +	spin_unlock(&priv->lock);
> +	if (!err)
> +		gntdev_free_map(map);
> +	return err;
> +}
> +
> +static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
> +					      struct ioctl_gntdev_get_offset_for_vaddr __user *u)
> +{
> +	struct ioctl_gntdev_get_offset_for_vaddr op;
> +	struct grant_map *map;
> +
> +	if (copy_from_user(&op, u, sizeof(op)) != 0)
> +		return -EFAULT;
> +	if (debug)
> +		printk("%s: priv %p, offset for vaddr %lx\n", __FUNCTION__, priv,
> +		       (unsigned long)op.vaddr);
> +
> +	spin_lock(&priv->lock);
> +	map = gntdev_find_map_vaddr(priv, op.vaddr);
> +	if (map == NULL ||
> +	    map->vma->vm_start != op.vaddr) {
> +		spin_unlock(&priv->lock);
> +		return -EINVAL;
> +	}
> +	op.offset = map->index << PAGE_SHIFT;
> +	op.count = map->count;
> +	spin_unlock(&priv->lock);
> +
> +	if (copy_to_user(u, &op, sizeof(op)) != 0)
> +		return -EFAULT;
> +	return 0;
> +}
> +
> +static long gntdev_ioctl_set_max_grants(struct gntdev_priv *priv,
> +					struct ioctl_gntdev_set_max_grants __user *u)
> +{
> +	struct ioctl_gntdev_set_max_grants op;
> +
> +	if (copy_from_user(&op, u, sizeof(op)) != 0)
> +		return -EFAULT;
> +	if (debug)
> +		printk("%s: priv %p, limit %d\n", __FUNCTION__, priv, op.count);
> +	if (op.count > limit)
> +		return -EINVAL;

Not -E2BIG?

> +
> +	spin_lock(&priv->lock);
> +	priv->limit = op.count;
> +	spin_unlock(&priv->lock);
> +	return 0;
> +}
> +
> +static long gntdev_ioctl(struct file *flip,
> +			 unsigned int cmd, unsigned long arg)
> +{
> +	struct gntdev_priv *priv = flip->private_data;
> +	void __user *ptr = (void __user *)arg;
> +
> +	switch (cmd) {
> +	case IOCTL_GNTDEV_MAP_GRANT_REF:
> +		return gntdev_ioctl_map_grant_ref(priv, ptr);
> +
> +	case IOCTL_GNTDEV_UNMAP_GRANT_REF:
> +		return gntdev_ioctl_unmap_grant_ref(priv, ptr);
> +
> +	case IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR:
> +		return gntdev_ioctl_get_offset_for_vaddr(priv, ptr);
> +
> +	case IOCTL_GNTDEV_SET_MAX_GRANTS:
> +		return gntdev_ioctl_set_max_grants(priv, ptr);
> +
> +	default:
> +		if (debug)
> +			printk("%s: priv %p, unknown cmd %x\n",
> +			       __FUNCTION__, priv, cmd);
> +		return -ENOIOCTLCMD;
> +	}
> +
> +	return 0;
> +}
> +
> +static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
> +{
> +	struct gntdev_priv *priv = flip->private_data;
> +	int index = vma->vm_pgoff;
> +	int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> +	struct grant_map *map;
> +	int err = -EINVAL;
> +
> +	if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
> +		return -EINVAL;
> +
> +	if (debug)
> +		printk("%s: map %d+%d at %lx (pgoff %lx)\n", __FUNCTION__,
> +		       index, count, vma->vm_start, vma->vm_pgoff);
> +
> +	spin_lock(&priv->lock);
> +	map = gntdev_find_map_index(priv, index, count);
> +	if (!map)
> +		goto unlock_out;
> +	if (map->vma)
> +		goto unlock_out;
> +	if (priv->mm != vma->vm_mm) {
> +		printk("%s: Huh? Other mm?\n", __FUNCTION__);
> +		goto unlock_out;
> +	}
> +
> +	vma->vm_ops = &gntdev_vmops;
> +
> +	vma->vm_flags |= VM_RESERVED;
> +	vma->vm_flags |= VM_DONTCOPY;
> +	vma->vm_flags |= VM_DONTEXPAND;

You can squish those.
> +
> +	vma->vm_private_data = map;
> +	map->vma = vma;
> +
> +	map->flags = GNTMAP_host_map | GNTMAP_application_map | GNTMAP_contains_pte;
> +	if (!(vma->vm_flags & VM_WRITE))
> +		map->flags |= GNTMAP_readonly;
> +
> +	err = apply_to_page_range(vma->vm_mm, vma->vm_start,
> +				  vma->vm_end - vma->vm_start,
> +				  find_grant_ptes, map);
> +	if (err) {
> +		goto unlock_out;
> +		if (debug)
> +			printk("%s: find_grant_ptes() failure.\n", __FUNCTION__);

Heh.. . You do a 'goto' and then 'if debug..' Swap them around.

> +	}
> +
> +	err = map_grant_pages(map);
> +	if (err) {
> +		goto unlock_out;
> +		if (debug)
> +			printk("%s: map_grant_pages() failure.\n", __FUNCTION__);

Ditto.
> +	}
> +	map->is_mapped = 1;
> +
> +unlock_out:
> +	spin_unlock(&priv->lock);
> +	return err;
> +}
> +
> +static const struct file_operations gntdev_fops = {
> +	.owner = THIS_MODULE,
> +	.open = gntdev_open,
> +	.release = gntdev_release,
> +	.mmap = gntdev_mmap,
> +	.unlocked_ioctl = gntdev_ioctl
> +};
> +
> +static struct miscdevice gntdev_miscdev = {
> +	.minor        = MISC_DYNAMIC_MINOR,
> +	.name         = "xen/gntdev",
> +	.fops         = &gntdev_fops,
> +};
> +
> +/* ------------------------------------------------------------------ */
> +
> +static int __init gntdev_init(void)
> +{
> +	int err;
> +
> +	if (!xen_domain())
> +		return -ENODEV;
> +
> +	err = misc_register(&gntdev_miscdev);
> +	if (err != 0) {
> +		printk(KERN_ERR "Could not register gntdev device\n");
> +		return err;
> +	}
> +	return 0;
> +}
> +
> +static void __exit gntdev_exit(void)
> +{
> +	misc_deregister(&gntdev_miscdev);
> +}
> +
> +module_init(gntdev_init);
> +module_exit(gntdev_exit);
> +
> +/* ------------------------------------------------------------------ */
> diff --git a/include/xen/gntdev.h b/include/xen/gntdev.h
> new file mode 100644
> index 0000000..8bd1467
> --- /dev/null
> +++ b/include/xen/gntdev.h
> @@ -0,0 +1,119 @@
> +/******************************************************************************
> + * gntdev.h
> + * 
> + * Interface to /dev/xen/gntdev.
> + * 
> + * Copyright (c) 2007, D G Murray
> + * 
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version 2
> + * as published by the Free Software Foundation; or, when distributed
> + * separately from the Linux kernel or incorporated into other
> + * software packages, subject to the following license:
> + * 
> + * Permission is hereby granted, free of charge, to any person obtaining a copy
> + * of this source file (the "Software"), to deal in the Software without
> + * restriction, including without limitation the rights to use, copy, modify,
> + * merge, publish, distribute, sublicense, and/or sell copies of the Software,
> + * and to permit persons to whom the Software is furnished to do so, subject to
> + * the following conditions:
> + * 
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + * 
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
> + * IN THE SOFTWARE.
> + */
> +
> +#ifndef __LINUX_PUBLIC_GNTDEV_H__
> +#define __LINUX_PUBLIC_GNTDEV_H__
> +
> +struct ioctl_gntdev_grant_ref {
> +	/* The domain ID of the grant to be mapped. */
> +	uint32_t domid;
> +	/* The grant reference of the grant to be mapped. */
> +	uint32_t ref;
> +};
> +
> +/*
> + * Inserts the grant references into the mapping table of an instance
> + * of gntdev. N.B. This does not perform the mapping, which is deferred
> + * until mmap() is called with @index as the offset.
> + */
> +#define IOCTL_GNTDEV_MAP_GRANT_REF \
> +_IOC(_IOC_NONE, 'G', 0, sizeof(struct ioctl_gntdev_map_grant_ref))
> +struct ioctl_gntdev_map_grant_ref {
> +	/* IN parameters */
> +	/* The number of grants to be mapped. */
> +	uint32_t count;
> +	uint32_t pad;
> +	/* OUT parameters */
> +	/* The offset to be used on a subsequent call to mmap(). */
> +	uint64_t index;
> +	/* Variable IN parameter. */
> +	/* Array of grant references, of size @count. */
> +	struct ioctl_gntdev_grant_ref refs[1];
> +};
> +
> +/*
> + * Removes the grant references from the mapping table of an instance of
> + * of gntdev. N.B. munmap() must be called on the relevant virtual address(es)
> + * before this ioctl is called, or an error will result.
> + */
> +#define IOCTL_GNTDEV_UNMAP_GRANT_REF \
> +_IOC(_IOC_NONE, 'G', 1, sizeof(struct ioctl_gntdev_unmap_grant_ref))       
> +struct ioctl_gntdev_unmap_grant_ref {
> +	/* IN parameters */
> +	/* The offset was returned by the corresponding map operation. */
> +	uint64_t index;
> +	/* The number of pages to be unmapped. */
> +	uint32_t count;
> +	uint32_t pad;
> +};
> +
> +/*
> + * Returns the offset in the driver's address space that corresponds
> + * to @vaddr. This can be used to perform a munmap(), followed by an
> + * UNMAP_GRANT_REF ioctl, where no state about the offset is retained by
> + * the caller. The number of pages that were allocated at the same time as
> + * @vaddr is returned in @count.
> + *
> + * N.B. Where more than one page has been mapped into a contiguous range, the
> + *      supplied @vaddr must correspond to the start of the range; otherwise
> + *      an error will result. It is only possible to munmap() the entire
> + *      contiguously-allocated range at once, and not any subrange thereof.
> + */
> +#define IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR \
> +_IOC(_IOC_NONE, 'G', 2, sizeof(struct ioctl_gntdev_get_offset_for_vaddr))
> +struct ioctl_gntdev_get_offset_for_vaddr {
> +	/* IN parameters */
> +	/* The virtual address of the first mapped page in a range. */
> +	uint64_t vaddr;
> +	/* OUT parameters */
> +	/* The offset that was used in the initial mmap() operation. */
> +	uint64_t offset;
> +	/* The number of pages mapped in the VM area that begins at @vaddr. */
> +	uint32_t count;
> +	uint32_t pad;
> +};
> +
> +/*
> + * Sets the maximum number of grants that may mapped at once by this gntdev
> + * instance.
> + *
> + * N.B. This must be called before any other ioctl is performed on the device.
> + */
> +#define IOCTL_GNTDEV_SET_MAX_GRANTS \
> +_IOC(_IOC_NONE, 'G', 3, sizeof(struct ioctl_gntdev_set_max_grants))
> +struct ioctl_gntdev_set_max_grants {
> +	/* IN parameter */
> +	/* The maximum number of grants that may be mapped at once. */
> +	uint32_t count;
> +};
> +
> +#endif /* __LINUX_PUBLIC_GNTDEV_H__ */
> -- 
> 1.5.6.5
> 
> 
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