[Libguestfs] [PATCH] library: per-handle locking support
Maros Zatko
mzatko at redhat.com
Thu May 29 10:21:39 UTC 2014
Introduces private pool of muteces (per_handle_locks) guarded by read-write
mutex (locks_lock) using guestfs__per_handle_lock_lock(g) and
guestfs__per_handle_lock_unlock(g), where g is current valid guestfs_h handle.
Above two are used in generator/c.ml at begin and end of each non-deamon call.
New lock can be created using guestfs__per_handle_lock_add(g) and
destroyed with guestfs__per_handle_lock_remove(g). These two are called
automatically too. First one is called by guestfs_create and second by
guestfs_destroy.
---
generator/c.ml | 10 ++++
src/Makefile.am | 1 +
src/handle.c | 4 ++
src/locking.c | 162 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
src/locking.h | 45 ++++++++++++++++
5 files changed, 222 insertions(+)
create mode 100644 src/locking.c
create mode 100644 src/locking.h
diff --git a/generator/c.ml b/generator/c.ml
index ee276dc..e67053e 100644
--- a/generator/c.ml
+++ b/generator/c.ml
@@ -788,6 +788,9 @@ and generate_internal_actions_h () =
pr "#define GUESTFS_INTERNAL_ACTIONS_H_\n";
pr "\n";
+ pr "#include \"locking.h\"\n";
+ pr "\n";
+
List.iter (
fun { c_name = c_name; style = style } ->
generate_prototype ~single_line:true ~newline:true ~handle:"g"
@@ -1569,6 +1572,9 @@ and generate_client_actions hash () =
handle_null_optargs optargs c_name;
+ pr " guestfs___per_handle_lock_lock (g);\n";
+ pr "\n";
+
pr " int trace_flag = g->trace;\n";
pr " struct trace_buffer trace_buffer;\n";
(match ret with
@@ -1617,6 +1623,10 @@ and generate_client_actions hash () =
trace_return name style "r";
);
pr "\n";
+
+ pr " guestfs___per_handle_lock_unlock (g);\n";
+ pr "\n";
+
pr " return r;\n";
pr "}\n";
pr "\n"
diff --git a/src/Makefile.am b/src/Makefile.am
index 3d06203..f1f42d0 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -118,6 +118,7 @@ libguestfs_la_SOURCES = \
libvirt-auth.c \
libvirt-domain.c \
listfs.c \
+ locking.c \
lpj.c \
match.c \
osinfo.c \
diff --git a/src/handle.c b/src/handle.c
index 719bbcd..8397157 100644
--- a/src/handle.c
+++ b/src/handle.c
@@ -84,6 +84,8 @@ guestfs_create_flags (unsigned flags, ...)
g = calloc (1, sizeof (*g));
if (!g) return NULL;
+ guestfs___per_handle_lock_add (g);
+
g->state = CONFIG;
g->conn = NULL;
@@ -305,6 +307,8 @@ guestfs_close (guestfs_h *g)
return;
}
+ guestfs___per_handle_lock_remove (g);
+
/* Remove the handle from the handles list. */
if (g->close_on_exit) {
gl_lock_lock (handles_lock);
diff --git a/src/locking.c b/src/locking.c
new file mode 100644
index 0000000..2a35fce
--- /dev/null
+++ b/src/locking.c
@@ -0,0 +1,162 @@
+/* libguestfs
+ * Copyright (C) 2009-2014 Red Hat Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+#include "glthread/lock.h"
+#include "ignore-value.h"
+
+#include "guestfs.h"
+#include "guestfs-internal.h"
+#include "guestfs-internal-actions.h"
+#include "guestfs_protocol.h"
+
+#include "locking.h"
+
+static gl_lock_t guestfs___lookup_lock_or_abort (guestfs_h *g, int *pos);
+static void guestfs___per_handle_lock_is_not_held (guestfs_h *g);
+static void ___shrink_lock_arrays (void);
+
+
+gl_lock_define (static, *per_handle_locks)
+gl_rwlock_define_initialized (static, locks_lock)
+
+/* items in handles array bijectively corresponds to items in per_handle_locks
+ */
+static guestfs_h ** handles;
+static size_t n_handles;
+
+
+static gl_lock_t
+guestfs___lookup_lock_or_abort (guestfs_h *g, int *pos)
+{
+ // this function should be called with locks_lock already held
+ for (size_t i = 0; i < n_handles; i++) {
+ if (handles[i] == g) {
+ if (pos != NULL) {
+ *pos = i;
+ }
+ return per_handle_locks[i];
+ }
+ }
+ // handle not found. aborting
+ error (g, _("guestfs lock handle not found"));
+ abort ();
+}
+
+static void
+guestfs___per_handle_lock_is_not_held (guestfs_h *g)
+{
+ // this function should be called with locks_lock already held
+
+ int i;
+ gl_lock_t l = guestfs___lookup_lock_or_abort (g, &i);
+
+ gl_lock_lock (l);
+ gl_lock_unlock (l);
+}
+
+void
+guestfs___per_handle_lock_add (guestfs_h *g)
+{
+ gl_rwlock_wrlock (locks_lock);
+
+ n_handles++;
+ per_handle_locks = realloc (per_handle_locks,
+ sizeof (*per_handle_locks) * n_handles);
+ handles = realloc (handles, sizeof (*handles) * n_handles);
+
+ gl_lock_init (per_handle_locks[n_handles - 1]);
+ handles[n_handles - 1] = g;
+
+ gl_rwlock_unlock (locks_lock);
+}
+
+static void
+___shrink_lock_arrays (void)
+{
+ // locks_lock should be held
+
+ int i;
+ guestfs___lookup_lock_or_abort (NULL, &i);
+
+ memmove (handles + i, handles + i + 1, (n_handles - i - 1)
+ * sizeof (*handles));
+ memmove (per_handle_locks + i, per_handle_locks + i + 1,
+ (n_handles - i - 1) * sizeof (*per_handle_locks));
+ if (handles == NULL || per_handle_locks == NULL) {
+ abort ();
+ }
+}
+
+void
+guestfs___per_handle_lock_remove (guestfs_h *g)
+{
+ // locks_lock prevents per_handle_locks manipulation within this module
+ // take write lock, since we're going to update guarded per_handle_locks
+ gl_rwlock_wrlock (locks_lock);
+
+ // ensure we don't get into data race when removing lock
+ guestfs___per_handle_lock_is_not_held (g);
+
+ int i;
+ gl_lock_t l = guestfs___lookup_lock_or_abort (g, &i);
+ gl_lock_destroy (l);
+ handles[i] = NULL;
+ // fill in hole we've created
+ ___shrink_lock_arrays ();
+
+ // and realloc
+ n_handles--;
+ if (n_handles > 0) {
+ per_handle_locks = realloc (per_handle_locks,
+ sizeof (*per_handle_locks) * n_handles);
+ handles = realloc (handles, sizeof (*handles) * n_handles);
+ }
+
+ gl_rwlock_unlock (locks_lock);
+}
+
+void
+guestfs___per_handle_lock_lock (guestfs_h *g)
+{
+ gl_rwlock_rdlock (locks_lock);
+
+ gl_lock_t l = guestfs___lookup_lock_or_abort(g, NULL);
+ gl_lock_lock(l);
+
+ gl_rwlock_unlock (locks_lock);
+}
+
+void
+guestfs___per_handle_lock_unlock (guestfs_h *g)
+{
+ gl_rwlock_rdlock (locks_lock);
+
+ gl_lock_t l = guestfs___lookup_lock_or_abort(g, NULL);
+ gl_lock_unlock(l);
+
+ gl_rwlock_unlock (locks_lock);
+}
+
diff --git a/src/locking.h b/src/locking.h
new file mode 100644
index 0000000..fc7bc46
--- /dev/null
+++ b/src/locking.h
@@ -0,0 +1,45 @@
+/* libguestfs
+ * Copyright (C) 2009-2014 Red Hat Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef _LOCKING_H
+#define _LOCKING_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <config.h>
+
+#include "glthread/lock.h"
+
+#include "guestfs.h"
+#include "guestfs-internal.h"
+
+extern void guestfs___per_handle_lock_add (guestfs_h *g);
+
+extern void guestfs___per_handle_lock_remove (guestfs_h *g);
+
+extern void guestfs___per_handle_lock_lock (guestfs_h *g);
+
+extern void guestfs___per_handle_lock_unlock (guestfs_h *g);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _LOCKING_H */
--
1.9.3
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