git » libjio » commit 8b08cec

Use posix_fadvise() in jtrans_add()

author Alberto Bertogli
2009-03-29 04:09:14 UTC
committer Alberto Bertogli
2009-03-29 04:14:26 UTC
parent 70ee2209c331e69bda9a6a7d02a138aac56d0797
Use posix_fadvise() in jtrans_add()

When adding an operation to a transaction, it's highly likely that the
affected region will be read when committing.

This patch lets the kernel know that using posix_fadvise(), so it can take
actions based on that.

Because posix_fadvise() was included in SUSv3 and so far we've relied just
on SUSv2, we introduce a new header, compat.h, to provide a stub for that
function so the library can be built in systems that do not implement it.

Signed-off-by: Alberto Bertogli <albertito@blitiri.com.ar>
libjio/Makefile +1 -1
libjio/compat.h +19 -0
libjio/trans.c +5 -0 
diff --git a/libjio/Makefile b/libjio/Makefile
index be29891..c3ab13e 100644
--- a/libjio/Makefile
+++ b/libjio/Makefile
@@ -3,7 +3,7 @@ CFLAGS = -std=c99 -pedantic -Wall -O3
 
 MANDATORY_CFLAGS := \
 	-D_LARGEFILE_SOURCE=1 $(shell getconf LFS_CFLAGS 2>/dev/null) \
-	-D_XOPEN_SOURCE=500
+	-D_XOPEN_SOURCE=600
 
 MANDATORY_LDFLAGS := $(shell getconf LFS_LIBS 2>/dev/null)
 
diff --git a/libjio/compat.h b/libjio/compat.h
new file mode 100644
index 0000000..ecc742a
--- /dev/null
+++ b/libjio/compat.h
@@ -0,0 +1,19 @@
+
+/* Header to provide fallbacks for compatibility purposes. */
+
+#ifndef _COMPAT_H
+#define _COMPAT_H
+
+/* posix_fadvise() was introduced in SUSv3. Because it's the only SUSv3
+ * function we rely on so far (everything else is SUSv2), we define a void
+ * fallback for systems that do not implement it.
+ *
+ * The check is based on POSIX_FADV_WILLNEED being defined, which is not very
+ * nice, but it's simple, it works and should be reliable. */
+#include <fcntl.h>
+#ifndef POSIX_FADV_WILLNEED
+#define posix_fadvise(fd, offset, len, advise)
+#endif
+
+#endif
+
diff --git a/libjio/trans.c b/libjio/trans.c
index dc38814..6fb6885 100644
--- a/libjio/trans.c
+++ b/libjio/trans.c
@@ -21,6 +21,7 @@
 
 #include "libjio.h"
 #include "common.h"
+#include "compat.h"
 
 
 /*
@@ -203,6 +204,10 @@ int jtrans_add(struct jtrans *ts, const void *buf, size_t count, off_t offset)
 	jop->pdata = NULL;
 	jop->locked = 0;
 
+	/* it's highly likely that jtrans_commit() will want to read the
+	 * current data, so we tell the kernel about that */
+	posix_fadvise(ts->fs->fd, offset, count, POSIX_FADV_WILLNEED);
+
 	return 1;
 }