New XS_SET_TARGET

Stubdomains (and probably other domain disagregation elements too)
need to be able to tinker with another domain.  This adds
XS_SET_TARGET so that XenStore allows domains to have permissions on
files on which the "target" has permissions.  This also adds
xs_set_target, called by the domain builder when the 'target' option
is used in the configuration.

Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>

6 files changed, 90 insertions, 2 deletions

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index acf6dd3918..7f20e30ca0 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -119,6 +119,7 @@ static char *sockmsg_string(enum xsd_sockmsg_type type)
 	case XS_ERROR: return "ERROR";
 	case XS_IS_DOMAIN_INTRODUCED: return "XS_IS_DOMAIN_INTRODUCED";
 	case XS_RESUME: return "RESUME";
+	case XS_SET_TARGET: return "SET_TARGET";
 	default:
 		return "**UNKNOWN**";
 	}
@@ -283,6 +284,8 @@ static int destroy_conn(void *_conn)
 				break;
 		close(conn->fd);
 	}
+        if (conn->target)
+                talloc_unlink(conn, conn->target);
 	list_del(&conn->list);
 	trace_destroy(conn, "connection");
 	return 0;
@@ -472,11 +475,13 @@ static enum xs_perm_type perm_for_conn(struct connection *conn,
 		mask &= ~XS_PERM_WRITE;
 
 	/* Owners and tools get it all... */
-	if (!conn->id || perms[0].id == conn->id)
+	if (!conn->id || perms[0].id == conn->id
+                || (conn->target && perms[0].id == conn->target->id))
 		return (XS_PERM_READ|XS_PERM_WRITE|XS_PERM_OWNER) & mask;
 
 	for (i = 1; i < num; i++)
-		if (perms[i].id == conn->id)
+		if (perms[i].id == conn->id
+                        || (conn->target && perms[i].id == conn->target->id))
 			return perms[i].perms & mask;
 
 	return perms[0].perms & mask;
@@ -1245,6 +1250,10 @@ static void process_message(struct connection *conn, struct buffered_data *in)
 		do_resume(conn, onearg(in));
 		break;
 
+	case XS_SET_TARGET:
+		do_set_target(conn, in);
+		break;
+
 	default:
 		eprintf("Client unknown operation %i", in->hdr.msg.type);
 		send_error(conn, ENOSYS);
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index d46d77f026..975a97226f 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -84,6 +84,9 @@ struct connection
 	/* The domain I'm associated with, if any. */
 	struct domain *domain;
 
+        /* The target of the domain I'm associated with. */
+        struct connection *target;
+
 	/* My watches. */
 	struct list_head watches;
 
diff --git a/tools/xenstore/xenstored_domain.c b/tools/xenstore/xenstored_domain.c
index ed422a52aa..2cc9881eb4 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -381,6 +381,51 @@ void do_introduce(struct connection *conn, struct buffered_data *in)
 	send_ack(conn, XS_INTRODUCE);
 }
 
+void do_set_target(struct connection *conn, struct buffered_data *in)
+{
+	char *vec[2];
+	unsigned int domid, tdomid;
+        struct domain *domain, *tdomain;
+	if (get_strings(in, vec, ARRAY_SIZE(vec)) < ARRAY_SIZE(vec)) {
+		send_error(conn, EINVAL);
+		return;
+	}
+
+	if (conn->id != 0 || !conn->can_write) {
+		send_error(conn, EACCES);
+		return;
+	}
+
+	domid = atoi(vec[0]);
+	tdomid = atoi(vec[1]);
+
+        domain = find_domain_by_domid(domid);
+	if (!domain) {
+		send_error(conn, ENOENT);
+		return;
+	}
+        if (!domain->conn) {
+		send_error(conn, EINVAL);
+		return;
+	}
+
+        tdomain = find_domain_by_domid(tdomid);
+	if (!tdomain) {
+		send_error(conn, ENOENT);
+		return;
+	}
+
+        if (!tdomain->conn) {
+		send_error(conn, EINVAL);
+		return;
+	}
+
+        talloc_reference(domain->conn, tdomain->conn);
+        domain->conn->target = tdomain->conn;
+
+	send_ack(conn, XS_SET_TARGET);
+}
+
 /* domid */
 void do_release(struct connection *conn, const char *domid_str)
 {
diff --git a/tools/xenstore/xenstored_domain.h b/tools/xenstore/xenstored_domain.h
index 69fdb77c1a..f42a9f50ad 100644
--- a/tools/xenstore/xenstored_domain.h
+++ b/tools/xenstore/xenstored_domain.h
@@ -34,6 +34,9 @@ void do_release(struct connection *conn, const char *domid_str);
 /* domid */
 void do_resume(struct connection *conn, const char *domid_str);
 
+/* domid, target */
+void do_set_target(struct connection *conn, struct buffered_data *in);
+
 /* domid */
 void do_get_domain_path(struct connection *conn, const char *domid_str);
 
diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index a815257798..dbbf8ef394 100644
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -708,6 +708,25 @@ bool xs_introduce_domain(struct xs_handle *h,
 				ARRAY_SIZE(iov), NULL));
 }
 
+bool xs_set_target(struct xs_handle *h,
+			 unsigned int domid, unsigned int target)
+{
+	char domid_str[MAX_STRLEN(domid)];
+	char target_str[MAX_STRLEN(target)];
+	struct iovec iov[2];
+
+	snprintf(domid_str, sizeof(domid_str), "%u", domid);
+	snprintf(target_str, sizeof(target_str), "%u", target);
+
+	iov[0].iov_base = domid_str;
+	iov[0].iov_len = strlen(domid_str) + 1;
+	iov[1].iov_base = target_str;
+	iov[1].iov_len = strlen(target_str) + 1;
+
+	return xs_bool(xs_talkv(h, XBT_NULL, XS_SET_TARGET, iov,
+				ARRAY_SIZE(iov), NULL));
+}
+
 static void * single_with_domid(struct xs_handle *h,
 				enum xsd_sockmsg_type type,
 				unsigned int domid)
diff --git a/tools/xenstore/xs.h b/tools/xenstore/xs.h
index c855614675..dd8cbf8c95 100644
--- a/tools/xenstore/xs.h
+++ b/tools/xenstore/xs.h
@@ -132,6 +132,15 @@ bool xs_introduce_domain(struct xs_handle *h,
 			 unsigned int domid,
 			 unsigned long mfn,
                          unsigned int eventchn); 
+
+/* Set the target of a domain
+ * This tells the store daemon that a domain is targetting another one, so
+ * it should let it tinker with it.
+ */
+bool xs_set_target(struct xs_handle *h,
+		   unsigned int domid,
+		   unsigned int target);
+
 /* Resume a domain.
  * Clear the shutdown flag for this domain in the store.
  */