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authorJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-04-11 10:41:07 +0300
committerJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-04-13 08:17:18 +0300
commite09b41010ba33a20a87472ee821fa407a5b8da36 (patch)
treed10dc367189862e7ca5c592f033dc3726e1df4e3 /kernel/include/xen
parentf93b97fd65072de626c074dbe099a1fff05ce060 (diff)
These changes are the raw update to linux-4.4.6-rt14. Kernel sources
are taken from kernel.org, and rt patch from the rt wiki download page. During the rebasing, the following patch collided: Force tick interrupt and get rid of softirq magic(I70131fb85). Collisions have been removed because its logic was found on the source already. Change-Id: I7f57a4081d9deaa0d9ccfc41a6c8daccdee3b769 Signed-off-by: José Pekkarinen <jose.pekkarinen@nokia.com>
Diffstat (limited to 'kernel/include/xen')
-rw-r--r--kernel/include/xen/balloon.h12
-rw-r--r--kernel/include/xen/events.h1
-rw-r--r--kernel/include/xen/grant_table.h57
-rw-r--r--kernel/include/xen/interface/io/netif.h8
-rw-r--r--kernel/include/xen/interface/io/ring.h14
-rw-r--r--kernel/include/xen/interface/platform.h18
-rw-r--r--kernel/include/xen/interface/sched.h8
-rw-r--r--kernel/include/xen/interface/xen.h37
-rw-r--r--kernel/include/xen/interface/xenpmu.h94
-rw-r--r--kernel/include/xen/page.h33
-rw-r--r--kernel/include/xen/xen-ops.h10
-rw-r--r--kernel/include/xen/xenbus.h4
12 files changed, 259 insertions, 37 deletions
diff --git a/kernel/include/xen/balloon.h b/kernel/include/xen/balloon.h
index a4c1c6a93..d1767dfb0 100644
--- a/kernel/include/xen/balloon.h
+++ b/kernel/include/xen/balloon.h
@@ -8,30 +8,24 @@ struct balloon_stats {
/* We aim for 'current allocation' == 'target allocation'. */
unsigned long current_pages;
unsigned long target_pages;
+ unsigned long target_unpopulated;
/* Number of pages in high- and low-memory balloons. */
unsigned long balloon_low;
unsigned long balloon_high;
+ unsigned long total_pages;
unsigned long schedule_delay;
unsigned long max_schedule_delay;
unsigned long retry_count;
unsigned long max_retry_count;
-#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
- unsigned long hotplug_pages;
- unsigned long balloon_hotplug;
-#endif
};
extern struct balloon_stats balloon_stats;
void balloon_set_new_target(unsigned long target);
-int alloc_xenballooned_pages(int nr_pages, struct page **pages,
- bool highmem);
+int alloc_xenballooned_pages(int nr_pages, struct page **pages);
void free_xenballooned_pages(int nr_pages, struct page **pages);
-struct page *get_balloon_scratch_page(void);
-void put_balloon_scratch_page(void);
-
struct device;
#ifdef CONFIG_XEN_SELFBALLOONING
extern int register_xen_selfballooning(struct device *dev);
diff --git a/kernel/include/xen/events.h b/kernel/include/xen/events.h
index 7d95fdf9c..88da2abaf 100644
--- a/kernel/include/xen/events.h
+++ b/kernel/include/xen/events.h
@@ -92,7 +92,6 @@ void xen_hvm_callback_vector(void);
#ifdef CONFIG_TRACING
#define trace_xen_hvm_callback_vector xen_hvm_callback_vector
#endif
-extern int xen_have_vector_callback;
int xen_set_callback_via(uint64_t via);
void xen_evtchn_do_upcall(struct pt_regs *regs);
void xen_hvm_evtchn_do_upcall(void);
diff --git a/kernel/include/xen/grant_table.h b/kernel/include/xen/grant_table.h
index 4478f4b4a..34b1379f9 100644
--- a/kernel/include/xen/grant_table.h
+++ b/kernel/include/xen/grant_table.h
@@ -45,8 +45,10 @@
#include <asm/xen/hypervisor.h>
#include <xen/features.h>
+#include <xen/page.h>
#include <linux/mm_types.h>
#include <linux/page-flags.h>
+#include <linux/kernel.h>
#define GNTTAB_RESERVED_XENSTORE 1
@@ -129,6 +131,15 @@ void gnttab_cancel_free_callback(struct gnttab_free_callback *callback);
void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
unsigned long frame, int readonly);
+/* Give access to the first 4K of the page */
+static inline void gnttab_page_grant_foreign_access_ref_one(
+ grant_ref_t ref, domid_t domid,
+ struct page *page, int readonly)
+{
+ gnttab_grant_foreign_access_ref(ref, domid, xen_page_to_gfn(page),
+ readonly);
+}
+
void gnttab_grant_foreign_transfer_ref(grant_ref_t, domid_t domid,
unsigned long pfn);
@@ -224,4 +235,50 @@ static inline struct xen_page_foreign *xen_page_foreign(struct page *page)
#endif
}
+/* Split Linux page in chunk of the size of the grant and call fn
+ *
+ * Parameters of fn:
+ * gfn: guest frame number
+ * offset: offset in the grant
+ * len: length of the data in the grant.
+ * data: internal information
+ */
+typedef void (*xen_grant_fn_t)(unsigned long gfn, unsigned int offset,
+ unsigned int len, void *data);
+
+void gnttab_foreach_grant_in_range(struct page *page,
+ unsigned int offset,
+ unsigned int len,
+ xen_grant_fn_t fn,
+ void *data);
+
+/* Helper to get to call fn only on the first "grant chunk" */
+static inline void gnttab_for_one_grant(struct page *page, unsigned int offset,
+ unsigned len, xen_grant_fn_t fn,
+ void *data)
+{
+ /* The first request is limited to the size of one grant */
+ len = min_t(unsigned int, XEN_PAGE_SIZE - (offset & ~XEN_PAGE_MASK),
+ len);
+
+ gnttab_foreach_grant_in_range(page, offset, len, fn, data);
+}
+
+/* Get @nr_grefs grants from an array of page and call fn for each grant */
+void gnttab_foreach_grant(struct page **pages,
+ unsigned int nr_grefs,
+ xen_grant_fn_t fn,
+ void *data);
+
+/* Get the number of grant in a specified region
+ *
+ * start: Offset from the beginning of the first page
+ * len: total length of data (can cross multiple page)
+ */
+static inline unsigned int gnttab_count_grant(unsigned int start,
+ unsigned int len)
+{
+ return XEN_PFN_UP(xen_offset_in_page(start) + len);
+}
+
#endif /* __ASM_GNTTAB_H__ */
diff --git a/kernel/include/xen/interface/io/netif.h b/kernel/include/xen/interface/io/netif.h
index 70054cc07..252ffd480 100644
--- a/kernel/include/xen/interface/io/netif.h
+++ b/kernel/include/xen/interface/io/netif.h
@@ -156,7 +156,9 @@ struct xen_netif_tx_request {
/* Types of xen_netif_extra_info descriptors. */
#define XEN_NETIF_EXTRA_TYPE_NONE (0) /* Never used - invalid */
#define XEN_NETIF_EXTRA_TYPE_GSO (1) /* u.gso */
-#define XEN_NETIF_EXTRA_TYPE_MAX (2)
+#define XEN_NETIF_EXTRA_TYPE_MCAST_ADD (2) /* u.mcast */
+#define XEN_NETIF_EXTRA_TYPE_MCAST_DEL (3) /* u.mcast */
+#define XEN_NETIF_EXTRA_TYPE_MAX (4)
/* xen_netif_extra_info flags. */
#define _XEN_NETIF_EXTRA_FLAG_MORE (0)
@@ -201,6 +203,10 @@ struct xen_netif_extra_info {
uint16_t features; /* XEN_NETIF_GSO_FEAT_* */
} gso;
+ struct {
+ uint8_t addr[6]; /* Address to add/remove. */
+ } mcast;
+
uint16_t pad[3];
} u;
};
diff --git a/kernel/include/xen/interface/io/ring.h b/kernel/include/xen/interface/io/ring.h
index 7d28aff60..7dc685b40 100644
--- a/kernel/include/xen/interface/io/ring.h
+++ b/kernel/include/xen/interface/io/ring.h
@@ -181,6 +181,20 @@ struct __name##_back_ring { \
#define RING_GET_REQUEST(_r, _idx) \
(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
+/*
+ * Get a local copy of a request.
+ *
+ * Use this in preference to RING_GET_REQUEST() so all processing is
+ * done on a local copy that cannot be modified by the other end.
+ *
+ * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
+ * to be ineffective where _req is a struct which consists of only bitfields.
+ */
+#define RING_COPY_REQUEST(_r, _idx, _req) do { \
+ /* Use volatile to force the copy into _req. */ \
+ *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \
+} while (0)
+
#define RING_GET_RESPONSE(_r, _idx) \
(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
diff --git a/kernel/include/xen/interface/platform.h b/kernel/include/xen/interface/platform.h
index 5cc49ea8d..8e0358713 100644
--- a/kernel/include/xen/interface/platform.h
+++ b/kernel/include/xen/interface/platform.h
@@ -474,6 +474,23 @@ struct xenpf_core_parking {
};
DEFINE_GUEST_HANDLE_STRUCT(xenpf_core_parking);
+#define XENPF_get_symbol 63
+struct xenpf_symdata {
+ /* IN/OUT variables */
+ uint32_t namelen; /* size of 'name' buffer */
+
+ /* IN/OUT variables */
+ uint32_t symnum; /* IN: Symbol to read */
+ /* OUT: Next available symbol. If same as IN */
+ /* then we reached the end */
+
+ /* OUT variables */
+ GUEST_HANDLE(char) name;
+ uint64_t address;
+ char type;
+};
+DEFINE_GUEST_HANDLE_STRUCT(xenpf_symdata);
+
struct xen_platform_op {
uint32_t cmd;
uint32_t interface_version; /* XENPF_INTERFACE_VERSION */
@@ -495,6 +512,7 @@ struct xen_platform_op {
struct xenpf_cpu_hotadd cpu_add;
struct xenpf_mem_hotadd mem_add;
struct xenpf_core_parking core_parking;
+ struct xenpf_symdata symdata;
uint8_t pad[128];
} u;
};
diff --git a/kernel/include/xen/interface/sched.h b/kernel/include/xen/interface/sched.h
index 9ce083960..f18490985 100644
--- a/kernel/include/xen/interface/sched.h
+++ b/kernel/include/xen/interface/sched.h
@@ -107,5 +107,13 @@ struct sched_watchdog {
#define SHUTDOWN_suspend 2 /* Clean up, save suspend info, kill. */
#define SHUTDOWN_crash 3 /* Tell controller we've crashed. */
#define SHUTDOWN_watchdog 4 /* Restart because watchdog time expired. */
+/*
+ * Domain asked to perform 'soft reset' for it. The expected behavior is to
+ * reset internal Xen state for the domain returning it to the point where it
+ * was created but leaving the domain's memory contents and vCPU contexts
+ * intact. This will allow the domain to start over and set up all Xen specific
+ * interfaces again.
+ */
+#define SHUTDOWN_soft_reset 5
#endif /* __XEN_PUBLIC_SCHED_H__ */
diff --git a/kernel/include/xen/interface/xen.h b/kernel/include/xen/interface/xen.h
index a48378958..167071c29 100644
--- a/kernel/include/xen/interface/xen.h
+++ b/kernel/include/xen/interface/xen.h
@@ -80,6 +80,7 @@
#define __HYPERVISOR_kexec_op 37
#define __HYPERVISOR_tmem_op 38
#define __HYPERVISOR_xc_reserved_op 39 /* reserved for XenClient */
+#define __HYPERVISOR_xenpmu_op 40
/* Architecture-specific hypercall definitions. */
#define __HYPERVISOR_arch_0 48
@@ -112,6 +113,7 @@
#define VIRQ_MEM_EVENT 10 /* G. (DOM0) A memory event has occured */
#define VIRQ_XC_RESERVED 11 /* G. Reserved for XenClient */
#define VIRQ_ENOMEM 12 /* G. (DOM0) Low on heap memory */
+#define VIRQ_XENPMU 13 /* PMC interrupt */
/* Architecture-specific VIRQ definitions. */
#define VIRQ_ARCH_0 16
@@ -585,26 +587,29 @@ struct shared_info {
};
/*
- * Start-of-day memory layout for the initial domain (DOM0):
+ * Start-of-day memory layout
+ *
* 1. The domain is started within contiguous virtual-memory region.
* 2. The contiguous region begins and ends on an aligned 4MB boundary.
- * 3. The region start corresponds to the load address of the OS image.
- * If the load address is not 4MB aligned then the address is rounded down.
- * 4. This the order of bootstrap elements in the initial virtual region:
+ * 3. This the order of bootstrap elements in the initial virtual region:
* a. relocated kernel image
* b. initial ram disk [mod_start, mod_len]
+ * (may be omitted)
* c. list of allocated page frames [mfn_list, nr_pages]
+ * (unless relocated due to XEN_ELFNOTE_INIT_P2M)
* d. start_info_t structure [register ESI (x86)]
- * e. bootstrap page tables [pt_base, CR3 (x86)]
- * f. bootstrap stack [register ESP (x86)]
- * 5. Bootstrap elements are packed together, but each is 4kB-aligned.
- * 6. The initial ram disk may be omitted.
- * 7. The list of page frames forms a contiguous 'pseudo-physical' memory
+ * in case of dom0 this page contains the console info, too
+ * e. unless dom0: xenstore ring page
+ * f. unless dom0: console ring page
+ * g. bootstrap page tables [pt_base, CR3 (x86)]
+ * h. bootstrap stack [register ESP (x86)]
+ * 4. Bootstrap elements are packed together, but each is 4kB-aligned.
+ * 5. The list of page frames forms a contiguous 'pseudo-physical' memory
* layout for the domain. In particular, the bootstrap virtual-memory
* region is a 1:1 mapping to the first section of the pseudo-physical map.
- * 8. All bootstrap elements are mapped read-writable for the guest OS. The
+ * 6. All bootstrap elements are mapped read-writable for the guest OS. The
* only exception is the bootstrap page table, which is mapped read-only.
- * 9. There is guaranteed to be at least 512kB padding after the final
+ * 7. There is guaranteed to be at least 512kB padding after the final
* bootstrap element. If necessary, the bootstrap virtual region is
* extended by an extra 4MB to ensure this.
*/
@@ -641,10 +646,12 @@ struct start_info {
};
/* These flags are passed in the 'flags' field of start_info_t. */
-#define SIF_PRIVILEGED (1<<0) /* Is the domain privileged? */
-#define SIF_INITDOMAIN (1<<1) /* Is this the initial control domain? */
-#define SIF_MULTIBOOT_MOD (1<<2) /* Is mod_start a multiboot module? */
-#define SIF_MOD_START_PFN (1<<3) /* Is mod_start a PFN? */
+#define SIF_PRIVILEGED (1<<0) /* Is the domain privileged? */
+#define SIF_INITDOMAIN (1<<1) /* Is this the initial control domain? */
+#define SIF_MULTIBOOT_MOD (1<<2) /* Is mod_start a multiboot module? */
+#define SIF_MOD_START_PFN (1<<3) /* Is mod_start a PFN? */
+#define SIF_VIRT_P2M_4TOOLS (1<<4) /* Do Xen tools understand a virt. mapped */
+ /* P->M making the 3 level tree obsolete? */
#define SIF_PM_MASK (0xFF<<8) /* reserve 1 byte for xen-pm options */
/*
diff --git a/kernel/include/xen/interface/xenpmu.h b/kernel/include/xen/interface/xenpmu.h
new file mode 100644
index 000000000..139efc91b
--- /dev/null
+++ b/kernel/include/xen/interface/xenpmu.h
@@ -0,0 +1,94 @@
+#ifndef __XEN_PUBLIC_XENPMU_H__
+#define __XEN_PUBLIC_XENPMU_H__
+
+#include "xen.h"
+
+#define XENPMU_VER_MAJ 0
+#define XENPMU_VER_MIN 1
+
+/*
+ * ` enum neg_errnoval
+ * ` HYPERVISOR_xenpmu_op(enum xenpmu_op cmd, struct xenpmu_params *args);
+ *
+ * @cmd == XENPMU_* (PMU operation)
+ * @args == struct xenpmu_params
+ */
+/* ` enum xenpmu_op { */
+#define XENPMU_mode_get 0 /* Also used for getting PMU version */
+#define XENPMU_mode_set 1
+#define XENPMU_feature_get 2
+#define XENPMU_feature_set 3
+#define XENPMU_init 4
+#define XENPMU_finish 5
+#define XENPMU_lvtpc_set 6
+#define XENPMU_flush 7
+
+/* ` } */
+
+/* Parameters structure for HYPERVISOR_xenpmu_op call */
+struct xen_pmu_params {
+ /* IN/OUT parameters */
+ struct {
+ uint32_t maj;
+ uint32_t min;
+ } version;
+ uint64_t val;
+
+ /* IN parameters */
+ uint32_t vcpu;
+ uint32_t pad;
+};
+
+/* PMU modes:
+ * - XENPMU_MODE_OFF: No PMU virtualization
+ * - XENPMU_MODE_SELF: Guests can profile themselves
+ * - XENPMU_MODE_HV: Guests can profile themselves, dom0 profiles
+ * itself and Xen
+ * - XENPMU_MODE_ALL: Only dom0 has access to VPMU and it profiles
+ * everyone: itself, the hypervisor and the guests.
+ */
+#define XENPMU_MODE_OFF 0
+#define XENPMU_MODE_SELF (1<<0)
+#define XENPMU_MODE_HV (1<<1)
+#define XENPMU_MODE_ALL (1<<2)
+
+/*
+ * PMU features:
+ * - XENPMU_FEATURE_INTEL_BTS: Intel BTS support (ignored on AMD)
+ */
+#define XENPMU_FEATURE_INTEL_BTS 1
+
+/*
+ * Shared PMU data between hypervisor and PV(H) domains.
+ *
+ * The hypervisor fills out this structure during PMU interrupt and sends an
+ * interrupt to appropriate VCPU.
+ * Architecture-independent fields of xen_pmu_data are WO for the hypervisor
+ * and RO for the guest but some fields in xen_pmu_arch can be writable
+ * by both the hypervisor and the guest (see arch-$arch/pmu.h).
+ */
+struct xen_pmu_data {
+ /* Interrupted VCPU */
+ uint32_t vcpu_id;
+
+ /*
+ * Physical processor on which the interrupt occurred. On non-privileged
+ * guests set to vcpu_id;
+ */
+ uint32_t pcpu_id;
+
+ /*
+ * Domain that was interrupted. On non-privileged guests set to
+ * DOMID_SELF.
+ * On privileged guests can be DOMID_SELF, DOMID_XEN, or, when in
+ * XENPMU_MODE_ALL mode, domain ID of another domain.
+ */
+ domid_t domain_id;
+
+ uint8_t pad[6];
+
+ /* Architecture-specific information */
+ struct xen_pmu_arch pmu;
+};
+
+#endif /* __XEN_PUBLIC_XENPMU_H__ */
diff --git a/kernel/include/xen/page.h b/kernel/include/xen/page.h
index c5ed20bb3..96294ac93 100644
--- a/kernel/include/xen/page.h
+++ b/kernel/include/xen/page.h
@@ -1,16 +1,41 @@
#ifndef _XEN_PAGE_H
#define _XEN_PAGE_H
+#include <asm/page.h>
+
+/* The hypercall interface supports only 4KB page */
+#define XEN_PAGE_SHIFT 12
+#define XEN_PAGE_SIZE (_AC(1, UL) << XEN_PAGE_SHIFT)
+#define XEN_PAGE_MASK (~(XEN_PAGE_SIZE-1))
+#define xen_offset_in_page(p) ((unsigned long)(p) & ~XEN_PAGE_MASK)
+
+/*
+ * We assume that PAGE_SIZE is a multiple of XEN_PAGE_SIZE
+ * XXX: Add a BUILD_BUG_ON?
+ */
+
+#define xen_pfn_to_page(xen_pfn) \
+ ((pfn_to_page(((unsigned long)(xen_pfn) << XEN_PAGE_SHIFT) >> PAGE_SHIFT)))
+#define page_to_xen_pfn(page) \
+ (((page_to_pfn(page)) << PAGE_SHIFT) >> XEN_PAGE_SHIFT)
+
+#define XEN_PFN_PER_PAGE (PAGE_SIZE / XEN_PAGE_SIZE)
+
+#define XEN_PFN_DOWN(x) ((x) >> XEN_PAGE_SHIFT)
+#define XEN_PFN_UP(x) (((x) + XEN_PAGE_SIZE-1) >> XEN_PAGE_SHIFT)
+#define XEN_PFN_PHYS(x) ((phys_addr_t)(x) << XEN_PAGE_SHIFT)
+
#include <asm/xen/page.h>
-static inline unsigned long page_to_mfn(struct page *page)
+/* Return the GFN associated to the first 4KB of the page */
+static inline unsigned long xen_page_to_gfn(struct page *page)
{
- return pfn_to_mfn(page_to_pfn(page));
+ return pfn_to_gfn(page_to_xen_pfn(page));
}
struct xen_memory_region {
- phys_addr_t start;
- phys_addr_t size;
+ unsigned long start_pfn;
+ unsigned long n_pfns;
};
#define XEN_EXTRA_MEM_MAX_REGIONS 128 /* == E820MAX */
diff --git a/kernel/include/xen/xen-ops.h b/kernel/include/xen/xen-ops.h
index 0ce4f3201..e4e214a5a 100644
--- a/kernel/include/xen/xen-ops.h
+++ b/kernel/include/xen/xen-ops.h
@@ -30,7 +30,7 @@ void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order);
struct vm_area_struct;
/*
- * xen_remap_domain_mfn_array() - map an array of foreign frames
+ * xen_remap_domain_gfn_array() - map an array of foreign frames
* @vma: VMA to map the pages into
* @addr: Address at which to map the pages
* @gfn: Array of GFNs to map
@@ -46,14 +46,14 @@ struct vm_area_struct;
* Returns the number of successfully mapped frames, or a -ve error
* code.
*/
-int xen_remap_domain_mfn_array(struct vm_area_struct *vma,
+int xen_remap_domain_gfn_array(struct vm_area_struct *vma,
unsigned long addr,
xen_pfn_t *gfn, int nr,
int *err_ptr, pgprot_t prot,
unsigned domid,
struct page **pages);
-/* xen_remap_domain_mfn_range() - map a range of foreign frames
+/* xen_remap_domain_gfn_range() - map a range of foreign frames
* @vma: VMA to map the pages into
* @addr: Address at which to map the pages
* @gfn: First GFN to map.
@@ -65,12 +65,12 @@ int xen_remap_domain_mfn_array(struct vm_area_struct *vma,
* Returns the number of successfully mapped frames, or a -ve error
* code.
*/
-int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
+int xen_remap_domain_gfn_range(struct vm_area_struct *vma,
unsigned long addr,
xen_pfn_t gfn, int nr,
pgprot_t prot, unsigned domid,
struct page **pages);
-int xen_unmap_domain_mfn_range(struct vm_area_struct *vma,
+int xen_unmap_domain_gfn_range(struct vm_area_struct *vma,
int numpgs, struct page **pages);
int xen_xlate_remap_gfn_array(struct vm_area_struct *vma,
unsigned long addr,
diff --git a/kernel/include/xen/xenbus.h b/kernel/include/xen/xenbus.h
index 289c0b5f0..32b944b7c 100644
--- a/kernel/include/xen/xenbus.h
+++ b/kernel/include/xen/xenbus.h
@@ -46,8 +46,8 @@
#include <xen/interface/io/xenbus.h>
#include <xen/interface/io/xs_wire.h>
-#define XENBUS_MAX_RING_PAGE_ORDER 4
-#define XENBUS_MAX_RING_PAGES (1U << XENBUS_MAX_RING_PAGE_ORDER)
+#define XENBUS_MAX_RING_GRANT_ORDER 4
+#define XENBUS_MAX_RING_GRANTS (1U << XENBUS_MAX_RING_GRANT_ORDER)
#define INVALID_GRANT_HANDLE (~0U)
/* Register callback to watch this node. */