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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 5/6] xen-gntalloc: Userspace grant allocation driver
On 01/27/2011 01:52 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 21, 2011 at 10:59:07AM -0500, Daniel De Graaf wrote:
>> This allows a userspace application to allocate a shared page for
>> implementing inter-domain communication or device drivers. These
>> shared pages can be mapped using the gntdev device or by the kernel
>> in another domain.
>>
>> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
>> ---
>> drivers/xen/Kconfig | 8 +
>> drivers/xen/Makefile | 2 +
>> drivers/xen/gntalloc.c | 477
>> ++++++++++++++++++++++++++++++++++++++++++++++++
>> include/xen/gntalloc.h | 70 +++++++
>> 4 files changed, 557 insertions(+), 0 deletions(-)
>> create mode 100644 drivers/xen/gntalloc.c
>> create mode 100644 include/xen/gntalloc.h
>>
>> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
>> index 07bec09..a3d7afb 100644
>> --- a/drivers/xen/Kconfig
>> +++ b/drivers/xen/Kconfig
>> @@ -80,6 +80,14 @@ config XEN_GNTDEV
>> help
>> Allows userspace processes to use grants.
>>
>> +config XEN_GRANT_DEV_ALLOC
>> + tristate "User-space grant reference allocator driver"
>> + depends on XEN
>> + help
>> + Allows userspace processes to create pages with access granted
>> + to other domains. This can be used to implement frontend drivers
>> + or as part of an inter-domain shared memory channel.
>> +
>> config XEN_PLATFORM_PCI
>> tristate "xen platform pci device driver"
>> depends on XEN_PVHVM && PCI
>> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
>> index 5088cc2..9585a1d 100644
>> --- a/drivers/xen/Makefile
>> +++ b/drivers/xen/Makefile
>> @@ -10,6 +10,7 @@ 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-$(CONFIG_XEN_GRANT_DEV_ALLOC) += xen-gntalloc.o
>> obj-$(CONFIG_XENFS) += xenfs/
>> obj-$(CONFIG_XEN_SYS_HYPERVISOR) += sys-hypervisor.o
>> obj-$(CONFIG_XEN_PLATFORM_PCI) += xen-platform-pci.o
>> @@ -18,5 +19,6 @@ obj-$(CONFIG_XEN_DOM0) += pci.o
>>
>> xen-evtchn-y := evtchn.o
>> xen-gntdev-y := gntdev.o
>> +xen-gntalloc-y := gntalloc.o
>>
>> xen-platform-pci-y := platform-pci.o
>> diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
>> new file mode 100644
>> index 0000000..a230dc4
>> --- /dev/null
>> +++ b/drivers/xen/gntalloc.c
>> @@ -0,0 +1,477 @@
>> +/******************************************************************************
>> + * gntalloc.c
>> + *
>> + * Device for creating grant references (in user-space) that may be shared
>> + * with other domains.
>> + *
>> + * 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
>> + */
>> +
>> +/*
>> + * This driver exists to allow userspace programs in Linux to allocate
>> kernel
>> + * memory that will later be shared with another domain. Without this
>> device,
>> + * Linux userspace programs cannot create grant references.
>> + *
>> + * How this stuff works:
>> + * X -> granting a page to Y
>> + * Y -> mapping the grant from X
>> + *
>> + * 1. X uses the gntalloc device to allocate a page of kernel memory, P.
>> + * 2. X creates an entry in the grant table that says domid(Y) can access
>> P.
>> + * This is done without a hypercall unless the grant table needs
>> expansion.
>> + * 3. X gives the grant reference identifier, GREF, to Y.
>> + * 4. Y maps the page, either directly into kernel memory for use in a
>> backend
>> + * driver, or via a the gntdev device to map into the address space of
>> an
>> + * application running in Y. This is the first point at which Xen does
>> any
>> + * tracking of the page.
>> + * 5. A program in X mmap()s a segment of the gntalloc device that
>> corresponds
>> + * to the shared page, and can now communicate with Y over the shared
>> page.
>> + *
>> + *
>> + * NOTE TO USERSPACE LIBRARIES:
>> + * The grant allocation and mmap()ing are, naturally, two separate
>> operations.
>> + * You set up the sharing by calling the create ioctl() and then the
>> mmap().
>> + * Teardown requires munmap() and either close() or ioctl().
>> + *
>> + * WARNING: Since Xen does not allow a guest to forcibly end the use of a
>> grant
>> + * reference, this device can be used to consume kernel memory by leaving
>> grant
>> + * references mapped by another domain when an application exits. Therefore,
>> + * there is a global limit on the number of pages that can be allocated.
>> When
>> + * all references to the page are unmapped, it will be freed during the next
>> + * grant operation.
>> + */
>> +
>> +#include <linux/atomic.h>
>> +#include <linux/module.h>
>> +#include <linux/miscdevice.h>
>> +#include <linux/kernel.h>
>> +#include <linux/init.h>
>> +#include <linux/slab.h>
>> +#include <linux/fs.h>
>> +#include <linux/device.h>
>> +#include <linux/mm.h>
>> +#include <linux/uaccess.h>
>> +#include <linux/types.h>
>> +#include <linux/list.h>
>> +
>> +#include <xen/xen.h>
>> +#include <xen/page.h>
>> +#include <xen/grant_table.h>
>> +#include <xen/gntalloc.h>
>> +
>> +static int limit = 1024;
>> +module_param(limit, int, 0644);
>> +MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
>> + "the gntalloc device");
>> +
>> +static LIST_HEAD(gref_list);
>> +static DEFINE_SPINLOCK(gref_lock);
>> +static int gref_size;
>> +
>> +/* Metadata on a grant reference. */
>> +struct gntalloc_gref {
>> + struct list_head next_all; /* list entry gref_list */
>
> How about 'next_gref' ?
Seems like a good name. Will change.
>> + struct list_head next_file; /* list entry file->list, if open */
>> + struct page *page; /* The shared page */
>> + uint64_t file_index; /* File offset for mmap() */
>> + unsigned int users; /* Use count - when zero, waiting on Xen */
>> + grant_ref_t gref_id; /* The grant reference number */
>> +};
>> +
>> +struct gntalloc_file_private_data {
>> + struct list_head list;
>> + uint64_t index;
>> +};
>> +
>> +static void __del_gref(struct gntalloc_gref *gref);
>> +
>> +static void do_cleanup(void)
>> +{
>> + struct gntalloc_gref *gref, *n;
>> + list_for_each_entry_safe(gref, n, &gref_list, next_all) {
>> + if (!gref->users)
>> + __del_gref(gref);
>> + }
>> +}
>> +
>> +static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
>> + uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
>> +{
>> + int i, rc, readonly;
>> + LIST_HEAD(queue_all);
>> + LIST_HEAD(queue_file);
>> + struct gntalloc_gref *gref;
>> +
>> + readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
>> + rc = -ENOMEM;
>> + for (i = 0; i < op->count; i++) {
>> + gref = kzalloc(sizeof(*gref), GFP_KERNEL);
>> + if (!gref)
>> + goto undo;
>> + list_add_tail(&gref->next_all, &queue_all);
>> + list_add_tail(&gref->next_file, &queue_file);
>> + gref->users = 1;
>> + gref->file_index = op->index + i * PAGE_SIZE;
>> + gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
>> + if (!gref->page)
>> + goto undo;
>> +
>> + /* Grant foreign access to the page. */
>> + gref->gref_id = gnttab_grant_foreign_access(op->domid,
>> + pfn_to_mfn(page_to_pfn(gref->page)), readonly);
>> + if (gref->gref_id < 0) {
>> + rc = gref->gref_id;
>> + goto undo;
>> + }
>> + gref_ids[i] = gref->gref_id;
>> + }
>> +
>> + /* Add to gref lists. */
>> + spin_lock(&gref_lock);
>> + list_splice_tail(&queue_all, &gref_list);
>> + list_splice_tail(&queue_file, &priv->list);
>> + spin_unlock(&gref_lock);
>> +
>> + return 0;
>> +
>> +undo:
>> + list_for_each_entry(gref, &queue_file, next_file) {
>> + if (gref->page && gref->gref_id >= 0) {
>> + __del_gref(gref);
>> + } else {
>> + if (gref->page)
>> + __free_page(gref->page);
>> + list_del(&gref->next_all);
>
> Ohh, you are actually deleting them from queue_all, ah.
> Can you add a comment about that since the first time I read this
> I thought you were iterating over the queue_file and deleting
> from _that_ list. Tricky..
>
> Can collapse this deleting into __del_gref? Looks like
> you should just preface the gnttab with "if gref->page && gref->gref_id"
> and also the gref_size, and the "if (gref->page)" before deleting?
Yes, this can be collapsed into __del_gref. That will probably clarify
the deletion, but I'll stick a comment about __del_gref removing from
queue_all and not queue_file so it's clearer what will/won't break.
>
>> + kfree(gref);
>> + }
>> + }
>> +
>> + /* It's possible for the target domain to map the just-allocated grant
>> + * references by blindly guessing their IDs; if this is done, then
>> + * __del_gref will leave them in the queue_all list. They need to be
>> + * added to the global list so that we can free them when they are no
>> + * longer referenced.
>> + */
>> + if (unlikely(!list_empty(&queue_all))) {
>> + spin_lock(&gref_lock);
>> + list_splice_tail(&queue_all, &gref_list);
>> + spin_unlock(&gref_lock);
>> + }
>> + return rc;
>> +}
>> +
>> +static void __del_gref(struct gntalloc_gref *gref)
>> +{
>> + if (gnttab_query_foreign_access(gref->gref_id))
>> + return;
>> +
>> + if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
>> + return;
>> +
>> + gref_size--;
>> + list_del(&gref->next_all);
>> +
>> + __free_page(gref->page);
>> + kfree(gref);
>> +}
>> +
>> +/* finds contiguous grant references in a file, returns the first */
>> +static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data
>> *priv,
>> + uint64_t index, uint32_t count)
>> +{
>> + struct gntalloc_gref *rv = NULL, *gref;
>> + list_for_each_entry(gref, &priv->list, next_file) {
>> + if (gref->file_index == index && !rv)
>> + rv = gref;
>> + if (rv) {
>> + if (gref->file_index != index)
>> + return NULL;
>> + index += PAGE_SIZE;
>> + count--;
>> + if (count == 0)
>> + return rv;
>> + }
>> + }
>> + return NULL;
>> +}
>> +
>> +/*
>> + * -------------------------------------
>> + * File operations.
>> + * -------------------------------------
>> + */
>> +static int gntalloc_open(struct inode *inode, struct file *filp)
>> +{
>> + struct gntalloc_file_private_data *priv;
>> +
>> + try_module_get(THIS_MODULE);
>
> No checking if it fails?
Actually, looking at it again, this seems redundant: won't open() itself
prevent rmmod of the module until everything is closed?
Regardless, while the failure seems unlikely it should be checked for.
>> +
>> + priv = kzalloc(sizeof(*priv), GFP_KERNEL);
>> + if (!priv)
>> + goto out_nomem;
>> + INIT_LIST_HEAD(&priv->list);
>> +
>> + filp->private_data = priv;
>> +
>> + pr_debug("%s: priv %p\n", __func__, priv);
>> +
>> + return 0;
>> +
>> +out_nomem:
>
> You should also do:
>
> module_put(THIS_MODULE);
>
Agreed, or just get rid of the module_get.
>> + return -ENOMEM;
>> +}
>> +
>> +static int gntalloc_release(struct inode *inode, struct file *filp)
>> +{
>> + struct gntalloc_file_private_data *priv = filp->private_data;
>> + struct gntalloc_gref *gref;
>> +
>> + pr_debug("%s: priv %p\n", __func__, priv);
>> +
>> + spin_lock(&gref_lock);
>> + while (!list_empty(&priv->list)) {
>> + gref = list_entry(priv->list.next,
>> + struct gntalloc_gref, next_file);
>
>
>> + list_del(&gref->next_file);
>> + gref->users--;
>> + if (gref->users == 0)
>> + __del_gref(gref);
>> + }
>> + kfree(priv);
>> + spin_unlock(&gref_lock);
>> +
>> + module_put(THIS_MODULE);
>> +
>> + return 0;
>> +}
>> +
>> +static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
>> + struct ioctl_gntalloc_alloc_gref __user *arg)
>> +{
>> + int rc = 0;
>> + struct ioctl_gntalloc_alloc_gref op;
>> + uint32_t *gref_ids;
>> +
>> + pr_debug("%s: priv %p\n", __func__, priv);
>> +
>> + if (copy_from_user(&op, arg, sizeof(op))) {
>> + rc = -EFAULT;
>> + goto out;
>> + }
>> +
>> + gref_ids = kzalloc(sizeof(gref_ids[0]) * op.count, GFP_TEMPORARY);
>> + if (!gref_ids) {
>> + rc = -ENOMEM;
>> + goto out;
>> + }
>> +
>> + spin_lock(&gref_lock);
>> + do_cleanup();
>
> Hmm, why the cleanup here? I see it gntalloc_ioctl_dealloc
> which makes sense since the users-- might have been decremented to zero.
> But here?
This is to clean up pages that were at zero (local) users but were still
mapped by remote domains. Since those pages count towards the limit that
we are about to enforce, it is a good idea to remove any pages that have
been unmapped by remote domains since last time we checked.
This would be much cleaner if Xen allowed a domain to force others to
unmap its pages, but that's a significant change to the semantics of
shared memory in the hypervisor.
>> + if (gref_size + op.count > limit) {
>> + spin_unlock(&gref_lock);
>> + rc = -ENOSPC;
>> + goto out_free;
>> + }
>> + gref_size += op.count;
>> + op.index = priv->index;
>> + priv->index += op.count * PAGE_SIZE;
>> + spin_unlock(&gref_lock);
>> +
>> + rc = add_grefs(&op, gref_ids, priv);
>> + if (rc < 0)
>> + goto out_free;
>> +
>> + if (copy_to_user(arg, &op, sizeof(op))) {
>> + rc = -EFAULT;
>> + goto out_free;
>
> Not something that would clean the newly added grant? Say
> the code I suggested below the 'out' label.
>
That races with a concurrent removal operation that has guessed
the offset we just added, and removed the gref. As soon as we unlock
gref_lock at the end of add_grefs, gref is unsafe to dereference.
This could be solved by a per-file lock, or by holding gref_lock
for longer, but the copy_to_user producing -EFAULT seemed unlikely
enough that forcing a close() seemed the better choice - especially
since the userspace application will be segfaulting soon if it is
trying to read the offsets.
>> + }
>> + if (copy_to_user(arg->gref_ids, gref_ids,
>> + sizeof(gref_ids[0]) * op.count)) {
>> + rc = -EFAULT;
>> + goto out_free;
>
> Ditto.
>> + }
>> +
>> +out_free:
>> + kfree(gref_ids);
>> +out:
>> + return rc;
>
> out_del_gref:
> gref->users--;
> __del_gref(gref);
>
> goto out_free;
>> +}
>> +
>> +static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
>> + void __user *arg)
>> +{
>> + int i, rc = 0;
>> + struct ioctl_gntalloc_dealloc_gref op;
>> + struct gntalloc_gref *gref, *n;
>> +
>> + pr_debug("%s: priv %p\n", __func__, priv);
>> +
>> + if (copy_from_user(&op, arg, sizeof(op))) {
>> + rc = -EFAULT;
>> + goto dealloc_grant_out;
>> + }
>> +
>> + spin_lock(&gref_lock);
>> + gref = find_grefs(priv, op.index, op.count);
>> + if (gref) {
>> + for (i = 0; i < op.count; i++) {
>> + n = list_entry(gref->next_file.next,
>> + struct gntalloc_gref, next_file);
>
> Might want to add a comment that you are deleting only from ->next_file
> b/c the do_cleanpup will take of deleting from the other list (that is
> if the users is at zero).
Right.
>> + list_del(&gref->next_file);
>> + gref->users--;
>> + gref = n;
>> + }
>> + } else {
>> + rc = -EINVAL;
>> + }
>> +
>> + do_cleanup();
>> +
>> + spin_unlock(&gref_lock);
>> +dealloc_grant_out:
>> + return rc;
>> +}
>> +
>> +static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
>> + unsigned long arg)
>> +{
>> + struct gntalloc_file_private_data *priv = filp->private_data;
>> +
>> + switch (cmd) {
>> + case IOCTL_GNTALLOC_ALLOC_GREF:
>> + return gntalloc_ioctl_alloc(priv, (void __user *)arg);
>> +
>> + case IOCTL_GNTALLOC_DEALLOC_GREF:
>> + return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
>> +
>> + default:
>> + return -ENOIOCTLCMD;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static void gntalloc_vma_close(struct vm_area_struct *vma)
>> +{
>> + struct gntalloc_gref *gref = vma->vm_private_data;
>> + if (!gref)
>> + return;
>> +
>> + spin_lock(&gref_lock);
>> + gref->users--;
>> + if (gref->users == 0)
>> + __del_gref(gref);
>
> I just want to be convienced here that I am wrong.
>
> If the 'ioctl_deallo' has not been done, what will if unmap this VMA?
> Will it be OK to yank the gref from gref_list while (and kfree it) while
> it is still referenced in the filp->private_data? Or would end up trying
> to derefence the *priv and go BOOM?
The VMA itself is unmapped regardless. The gref structure (and the pages
pointed to by the vma) is deallocated when the last reference goes away.
In your example, it would be on _release() of the file or a later dealloc
ioctl.
The only time __del_gref is called here is when the file has been closed
or the segment has already had ioctl_dealloc run on it.
>> + spin_unlock(&gref_lock);
>> +}
>> +
>> +static struct vm_operations_struct gntalloc_vmops = {
>> + .close = gntalloc_vma_close,
>> +};
>> +
>> +static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
>> +{
>> + struct gntalloc_file_private_data *priv = filp->private_data;
>> + struct gntalloc_gref *gref;
>> + int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
>> + int rv, i;
>> +
>> + pr_debug("%s: priv %p, page %lu+%d\n", __func__,
>> + priv, vma->vm_pgoff, count);
>> +
>> + if (!(vma->vm_flags & VM_SHARED)) {
>> + printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
>> + return -EINVAL;
>> + }
>> +
>> + spin_lock(&gref_lock);
>> + gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
>> + if (gref == NULL) {
>> + rv = -ENOENT;
>> + pr_debug("%s: Could not find grant reference",
>> + __func__);
>> + goto out_unlock;
>> + }
>> +
>> + vma->vm_private_data = gref;
>> +
>> + vma->vm_flags |= VM_RESERVED;
>> + vma->vm_flags |= VM_DONTCOPY;
>> + vma->vm_flags |= VM_IO;
>
> Hmm, I don't think you need the VM_IO.
Agreed, in fact it'll probably trigger warnings now that we force VM_IO
to imply pfn=mfn.
>> + vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP;
>> +
>> + vma->vm_ops = &gntalloc_vmops;
>> +
>> + for (i = 0; i < count; i++) {
>> + gref->users++;
>> + rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
>> + gref->page);
>> + if (rv)
>> + goto out_unlock;
>> +
>> + gref = list_entry(gref->next_file.next,
>> + struct gntalloc_gref, next_file);
>> + }
>> + rv = 0;
>> +
>> +out_unlock:
>> + spin_unlock(&gref_lock);
>> + return rv;
>> +}
>> +
>> +static const struct file_operations gntalloc_fops = {
>> + .owner = THIS_MODULE,
>> + .open = gntalloc_open,
>> + .release = gntalloc_release,
>> + .unlocked_ioctl = gntalloc_ioctl,
>> + .mmap = gntalloc_mmap
>> +};
>> +
>> +/*
>> + * -------------------------------------
>> + * Module creation/destruction.
>> + * -------------------------------------
>> + */
>> +static struct miscdevice gntalloc_miscdev = {
>> + .minor = MISC_DYNAMIC_MINOR,
>> + .name = "xen/gntalloc",
>> + .fops = &gntalloc_fops,
>> +};
>> +
>> +static int __init gntalloc_init(void)
>> +{
>> + int err;
>> +
>> + if (!xen_domain())
>> + return -ENODEV;
>> +
>> + err = misc_register(&gntalloc_miscdev);
>> + if (err != 0) {
>> + printk(KERN_ERR "Could not register misc gntalloc device\n");
>> + return err;
>> + }
>> +
>> + pr_debug("Created grant allocation device at %d,%d\n",
>> + MISC_MAJOR, gntalloc_miscdev.minor);
>> +
>> + return 0;
>> +}
>> +
>> +static void __exit gntalloc_exit(void)
>> +{
>> + misc_deregister(&gntalloc_miscdev);
>> +}
>> +
>> +module_init(gntalloc_init);
>> +module_exit(gntalloc_exit);
>> +
>> +MODULE_LICENSE("GPL");
>> +MODULE_AUTHOR("Carter Weatherly <carter.weatherly@xxxxxxxxxx>, "
>> + "Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>");
>> +MODULE_DESCRIPTION("User-space grant reference allocator driver");
>> diff --git a/include/xen/gntalloc.h b/include/xen/gntalloc.h
>> new file mode 100644
>> index 0000000..e1d6d0f
>> --- /dev/null
>> +++ b/include/xen/gntalloc.h
>> @@ -0,0 +1,70 @@
>> +/******************************************************************************
>> + * gntalloc.h
>> + *
>
> Copyright?
Public domain. The GPL text will need to be removed.
>> + * Interface to /dev/xen/gntalloc.
>> + *
>> + * 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_GNTALLOC_H__
>> +#define __LINUX_PUBLIC_GNTALLOC_H__
>> +
>> +/*
>> + * Allocates a new page and creates a new grant reference.
>> + */
>> +#define IOCTL_GNTALLOC_ALLOC_GREF \
>> +_IOC(_IOC_NONE, 'G', 5, sizeof(struct ioctl_gntalloc_alloc_gref))
>> +struct ioctl_gntalloc_alloc_gref {
>> + /* IN parameters */
>> + /* The ID of the domain to be given access to the grants. */
>> + uint16_t domid;
>> + /* Flags for this mapping */
>> + uint16_t flags;
>> + /* Number of pages to map */
>> + uint32_t count;
>> + /* OUT parameters */
>> + /* The offset to be used on a subsequent call to mmap(). */
>> + uint64_t index;
>> + /* The grant references of the newly created grant, one per page */
>> + /* Variable size, depending on count */
>> + uint32_t gref_ids[1];
>> +};
>> +
>> +#define GNTALLOC_FLAG_WRITABLE 1
>> +
>> +/*
>> + * Deallocates the grant reference, allowing the associated page to be
>> freed if
>> + * no other domains are using it.
>> + */
>> +#define IOCTL_GNTALLOC_DEALLOC_GREF \
>> +_IOC(_IOC_NONE, 'G', 6, sizeof(struct ioctl_gntalloc_dealloc_gref))
>> +struct ioctl_gntalloc_dealloc_gref {
>> + /* IN parameters */
>> + /* The offset returned in the map operation */
>> + uint64_t index;
>> + /* Number of references to unmap */
>> + uint32_t count;
>> +};
>> +#endif /* __LINUX_PUBLIC_GNTALLOC_H__ */
>> --
>> 1.7.3.4
>>
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