[v6,04/14] tools/xenstore: add framework to commit accounting data on success only

Commit Message

Jürgen Groß May 30, 2023, 8:24 a.m. UTC

Instead of modifying accounting data and undo those modifications in
case of an error during further processing, add a framework for
collecting the needed changes and commit them only when the whole
operation has succeeded.

This scheme can reuse large parts of the per transaction accounting.
The changed_domain handling can be reused, but the array size of the
accounting data should be possible to be different for both use cases.

Signed-off-by: Juergen Gross <[e-mail]>
Reviewed-by: Julien Grall <[e-mail]>
---
V3:
- call acc_commit() earlier (Julien Grall)
- add assert() to acc_commit()
- use fixed sized acc array in struct changed_domain (Julien Grall)
V5:
- set conn->in to NULL only locally in acc_commit() (Julien Grall)
- define ACC_CHD_N in enum (Julien Grall)
---
 tools/xenstore/xenstored_core.c   |  7 ++++
 tools/xenstore/xenstored_core.h   |  3 ++
 tools/xenstore/xenstored_domain.c | 54 ++++++++++++++++++++++++++++++-
 tools/xenstore/xenstored_domain.h |  6 +++-
 4 files changed, 68 insertions(+), 2 deletions(-)

Patch

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 3ca68681e3..8392bdec9b 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1023,6 +1023,9 @@  static void send_error(struct connection *conn, int error)
 			break;
 		}
 	}
+
+	acc_drop(conn);
+
 	send_reply(conn, XS_ERROR, xsd_errors[i].errstring,
 			  strlen(xsd_errors[i].errstring) + 1);
 }
@@ -1034,6 +1037,9 @@  void send_reply(struct connection *conn, enum xsd_sockmsg_type type,
 
 	assert(type != XS_WATCH_EVENT);
 
+	/* Commit accounting now, as later errors won't undo any changes. */
+	acc_commit(conn);
+
 	if ( len > XENSTORE_PAYLOAD_MAX ) {
 		send_error(conn, E2BIG);
 		return;
@@ -2195,6 +2201,7 @@  struct connection *new_connection(const struct interface_funcs *funcs)
 	new->is_stalled = false;
 	new->transaction_started = 0;
 	INIT_LIST_HEAD(&new->out_list);
+	INIT_LIST_HEAD(&new->acc_list);
 	INIT_LIST_HEAD(&new->ref_list);
 	INIT_LIST_HEAD(&new->watches);
 	INIT_LIST_HEAD(&new->transaction_list);
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index c59b06551f..1f811f38cb 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -139,6 +139,9 @@  struct connection
 	struct list_head out_list;
 	uint64_t timeout_msec;
 
+	/* Not yet committed accounting data (valid if in != NULL). */
+	struct list_head acc_list;
+
 	/* Referenced requests no longer pending. */
 	struct list_head ref_list;
 
diff --git a/tools/xenstore/xenstored_domain.c b/tools/xenstore/xenstored_domain.c
index 30fb9acec6..e59e40088e 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -100,7 +100,7 @@  struct changed_domain
 	unsigned int domid;
 
 	/* Accounting data. */
-	int acc[ACC_TR_N];
+	int acc[ACC_CHD_N];
 };
 
 static struct hashtable *domhash;
@@ -1070,6 +1070,7 @@  static int domain_acc_add(struct connection *conn, unsigned int domid,
 			  enum accitem what, int add, bool no_dom_alloc)
 {
 	struct domain *d;
+	struct changed_domain *cd;
 	struct list_head *head;
 	int ret;
 
@@ -1090,6 +1091,22 @@  static int domain_acc_add(struct connection *conn, unsigned int domid,
 		}
 	}
 
+	/* Temporary accounting data until final commit? */
+	if (conn && conn->in && what < ACC_REQ_N) {
+		/* Consider transaction local data. */
+		ret = 0;
+		if (conn->transaction && what < ACC_TR_N) {
+			head = transaction_get_changed_domains(
+				conn->transaction);
+			cd = acc_find_changed_domain(head, domid);
+			if (cd)
+				ret = cd->acc[what];
+		}
+		ret += acc_add_changed_dom(conn->in, &conn->acc_list, what,
+					   add, domid);
+		return errno ? -1 : domain_acc_add_valid(d, what, ret);
+	}
+
 	if (conn && conn->transaction && what < ACC_TR_N) {
 		head = transaction_get_changed_domains(conn->transaction);
 		ret = acc_add_changed_dom(conn->transaction, head, what,
@@ -1106,6 +1123,41 @@  static int domain_acc_add(struct connection *conn, unsigned int domid,
 	return d->acc[what];
 }
 
+void acc_drop(struct connection *conn)
+{
+	struct changed_domain *cd;
+
+	while ((cd = list_top(&conn->acc_list, struct changed_domain, list))) {
+		list_del(&cd->list);
+		talloc_free(cd);
+	}
+}
+
+void acc_commit(struct connection *conn)
+{
+	struct changed_domain *cd;
+	enum accitem what;
+	struct buffered_data *in = conn->in;
+
+	/*
+	 * Make sure domain_acc_add() below can't add additional data to
+	 * to be committed accounting records.
+	 */
+	conn->in = NULL;
+
+	while ((cd = list_top(&conn->acc_list, struct changed_domain, list))) {
+		list_del(&cd->list);
+		for (what = 0; what < ACC_REQ_N; what++)
+			if (cd->acc[what])
+				domain_acc_add(conn, cd->domid, what,
+					       cd->acc[what], true);
+
+		talloc_free(cd);
+	}
+
+	conn->in = in;
+}
+
 int domain_nbentry_inc(struct connection *conn, unsigned int domid)
 {
 	return (domain_acc_add(conn, domid, ACC_NODES, 1, false) < 0)
diff --git a/tools/xenstore/xenstored_domain.h b/tools/xenstore/xenstored_domain.h
index 9d05eb01da..e40657216b 100644
--- a/tools/xenstore/xenstored_domain.h
+++ b/tools/xenstore/xenstored_domain.h
@@ -25,8 +25,10 @@ 
  * a per transaction array.
  */
 enum accitem {
-	ACC_NODES,
+	ACC_REQ_N,		/* Number of elements per request. */
+	ACC_NODES = ACC_REQ_N,
 	ACC_TR_N,		/* Number of elements per transaction. */
+	ACC_CHD_N = ACC_TR_N,	/* max(ACC_REQ_N, ACC_TR_N), for changed dom. */
 	ACC_N = ACC_TR_N,	/* Number of elements per domain. */
 };
 
@@ -113,6 +115,8 @@  int domain_get_quota(const void *ctx, struct connection *conn,
  * If "update" is true, "chk_quota" is ignored.
  */
 int acc_fix_domains(struct list_head *head, bool chk_quota, bool update);
+void acc_drop(struct connection *conn);
+void acc_commit(struct connection *conn);
 
 /* Write rate limiting */