[PATCH 4/24] [xen-unstable.hg] make xenstored use grantref rather than map_foreign_range (which only privileged domains can do)

[Alex Zeffertt <alex.zeffertt@eu.citrix.com>]

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This patch modifies the xenstore daemon to use xc_gnttab_map_grant_ref
instead of xc_map_foreign_range where available.

TODO: This will probably break linking on Solaris, since they don't have
stubs for the gntmap functions yet.

A previous version of this patch was sent to xen-devel. See
http://lists.xensource.com/archives/html/xen-devel/2008-07/msg00610.html

Signed-off-by: Diego Ongaro <diego.ongaro@citrix.com>
Signed-off-by: Alex Zeffertt <alex.zeffertt@eu.citrix.com>
---

diff -r 289762278873 tools/xenstore/xenstored_domain.c
--- a/tools/xenstore/xenstored_domain.c	Fri Aug 01 16:50:27 2008 +0100
+++ b/tools/xenstore/xenstored_domain.c	Fri Aug 01 16:50:28 2008 +0100
@@ -31,8 +31,10 @@
 #include "xenstored_watch.h"
 
 #include <xenctrl.h>
+#include <xen/grant_table.h>
 
 static int *xc_handle;
+static int *xcg_handle;
 static evtchn_port_t virq_port;
 
 int xce_handle = -1; 
@@ -173,8 +175,12 @@
 			eprintf("> Unbinding port %i failed!\n", domain->port);
 	}
 
-	if (domain->interface)
-		munmap(domain->interface, getpagesize());
+	if (domain->interface) {
+		if (*xcg_handle >= 0 && domain->domid != 0)
+			xc_gnttab_munmap(*xcg_handle, domain->interface, 1);
+		else
+			munmap(domain->interface, getpagesize());
+	}
 
 	fire_watches(NULL, "@releaseDomain", false);
 
@@ -343,9 +349,17 @@
 	domain = find_domain_by_domid(domid);
 
 	if (domain == NULL) {
-		interface = xc_map_foreign_range(
-			*xc_handle, domid,
-			getpagesize(), PROT_READ|PROT_WRITE, mfn);
+		if (*xcg_handle >= 0) {
+			/* this is the preferred method */
+			interface = xc_gnttab_map_grant_ref(
+				*xcg_handle, domid,
+				GNTTAB_RESERVED_XENSTORE,
+				PROT_READ|PROT_WRITE);
+		} else {
+			interface = xc_map_foreign_range(
+				*xc_handle, domid,
+				getpagesize(), PROT_READ|PROT_WRITE, mfn);
+		}
 		if (!interface) {
 			send_error(conn, errno);
 			return;
@@ -353,7 +367,10 @@
 		/* Hang domain off "in" until we're finished. */
 		domain = new_domain(in, domid, port);
 		if (!domain) {
-			munmap(interface, getpagesize());
+			if (*xcg_handle >= 0)
+				xc_gnttab_munmap(*xcg_handle, interface, 1);
+			else
+				munmap(interface, getpagesize());
 			send_error(conn, errno);
 			return;
 		}
@@ -542,6 +559,12 @@
 	return 0;
 }
 
+static int close_xcg_handle(void *_handle)
+{
+	xc_gnttab_close(*(int *)_handle);
+	return 0;
+}
+
 /* Returns the implicit path of a connection (only domains have this) */
 const char *get_implicit_path(const struct connection *conn)
 {
@@ -584,6 +607,7 @@
 {
 	int rc;
 
+	/* Open the hypervisor interface. */
 	xc_handle = talloc(talloc_autofree_context(), int);
 	if (!xc_handle)
 		barf_perror("Failed to allocate domain handle");
@@ -593,6 +617,17 @@
 		barf_perror("Failed to open connection to hypervisor");
 
 	talloc_set_destructor(xc_handle, close_xc_handle);
+
+	/* Open the gntdev interface. */
+	xcg_handle = talloc(talloc_autofree_context(), int);
+	if (!xcg_handle)
+		barf_perror("Failed to allocate domain gnttab handle");
+
+	*xcg_handle = xc_gnttab_open();
+	if (*xcg_handle < 0)
+		xprintf("WARNING: Failed to open connection to gnttab\n");
+	else
+		talloc_set_destructor(xcg_handle, close_xcg_handle);
 
 	xce_handle = xc_evtchn_open();
 



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