[lttng-dev] [PATCH lttng-modules] RFC: fix global_dirty_limit for kernel v4.2 and up

[Michael Jeanson]

global_dirty_limit was moved into wb_domain

See upstream commit :

  commit dcc25ae76eb7b8ff883eaaab57e30e8f2f085be3
  Author: Tejun Heo <tj at kernel.org>
  Date:   Fri May 22 18:23:22 2015 -0400

    writeback: move global_dirty_limit into wb_domain

    This patch is a part of the series to define wb_domain which
    represents a domain that wb's (bdi_writeback's) belong to and are
    measured against each other in.  This will enable IO backpressure
    propagation for cgroup writeback.

    global_dirty_limit exists to regulate the global dirty threshold which
    is a property of the wb_domain.  This patch moves hard_dirty_limit,
    dirty_lock, and update_time into wb_domain.

    This is pure reorganization and doesn't introduce any behavioral
    changes.

Signed-off-by: Michael Jeanson <mjeanson at efficios.com>
---
 wrapper/writeback.h | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/wrapper/writeback.h b/wrapper/writeback.h
index cdcbd58..22b2c16 100644
--- a/wrapper/writeback.h
+++ b/wrapper/writeback.h
@@ -25,11 +25,33 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#ifdef CONFIG_KALLSYMS_ALL
+#include <lttng-kernel-version.h>
 
+#ifdef CONFIG_KALLSYMS_ALL
 #include <linux/kallsyms.h>
 #include <wrapper/kallsyms.h>
 
+
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,2,0)
+
+static struct wb_domain *global_wb_domain_sym;
+
+static inline
+unsigned long wrapper_global_dirty_limit(void)
+{
+	if (!global_wb_domain_sym)
+		global_wb_domain_sym =
+			(void *) kallsyms_lookup_dataptr("global_wb_domain");
+	if (global_wb_domain_sym) {
+		return global_wb_domain_sym->dirty_limit;
+	} else {
+		printk_once(KERN_WARNING "LTTng: global_wb_domain symbol lookup failed.\n");
+		return 0;
+	}
+}
+#else
+
 static unsigned long *global_dirty_limit_sym;
 
 static inline
@@ -45,8 +67,9 @@ unsigned long wrapper_global_dirty_limit(void)
 		return 0;
 	}
 }
+#endif
 
-#else
+#else /* CONFIG_KALLSYMS_ALL */
 
 #include <linux/writeback.h>
 
-- 
2.7.4