libxc: add xc_gnttab_map_grant_ref_notify

Normally, when a userspace process mapping a grant crashes, the domain
providing the reference receives no indication that its peer has
crashed, possibly leading to unexpected freezes or timeouts. This
function provides a notification of the unmap by signalling an event
channel and/or clearing a specific byte in the page.

This also unifies the 3 very similar grant-mapping osdep interfaces into
a single function instead of introducing yet another minor variation.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

1 files changed, 32 insertions, 1 deletions

diff --git a/tools/include/xen-sys/Linux/gntdev.h b/tools/include/xen-sys/Linux/gntdev.h
index 8bd1467893..caf6fb47ba 100644
--- a/tools/include/xen-sys/Linux/gntdev.h
+++ b/tools/include/xen-sys/Linux/gntdev.h
@@ -66,7 +66,7 @@ struct ioctl_gntdev_map_grant_ref {
  * 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))       
+_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. */
@@ -116,4 +116,35 @@ struct ioctl_gntdev_set_max_grants {
 	uint32_t count;
 };
 
+/*
+ * Sets up an unmap notification within the page, so that the other side can do
+ * cleanup if this side crashes. Required to implement cross-domain robust
+ * mutexes or close notification on communication channels.
+ *
+ * Each mapped page only supports one notification; multiple calls referring to
+ * the same page overwrite the previous notification. You must clear the
+ * notification prior to the IOCTL_GNTALLOC_DEALLOC_GREF if you do not want it
+ * to occur.
+ */
+#define IOCTL_GNTDEV_SET_UNMAP_NOTIFY \
+_IOC(_IOC_NONE, 'G', 7, sizeof(struct ioctl_gntdev_unmap_notify))
+struct ioctl_gntdev_unmap_notify {
+	/* IN parameters */
+	/* Offset in the file descriptor for a byte within the page. This offset
+	 * is the result of the IOCTL_GNTDEV_MAP_GRANT_REF and is the same as
+	 * is used with mmap(). If using UNMAP_NOTIFY_CLEAR_BYTE, this is the byte
+	 * within the page to be cleared.
+	 */
+	uint64_t index;
+	/* Action(s) to take on unmap */
+	uint32_t action;
+	/* Event channel to notify */
+	uint32_t event_channel_port;
+};
+
+/* Clear (set to zero) the byte specified by index */
+#define UNMAP_NOTIFY_CLEAR_BYTE 0x1
+/* Send an interrupt on the indicated event channel */
+#define UNMAP_NOTIFY_SEND_EVENT 0x2
+
 #endif /* __LINUX_PUBLIC_GNTDEV_H__ */