[PATCH] implement posix_fadvise64()

An implementation of posix_fadvise64().  It adds 368 bytes to my vmlinux and
is worth it.

I didn't bother doing posix_fadvise(), as userspace can implement that by
calling fadvise64().

The main reason for wanting this syscall is to provide userspace with the
ability to explicitly shoot down pagecache when streaming large files.  This
is what O_STEAMING does, only posix_fadvise() is standards-based, and harder
to use.

posix_fadvise() also subsumes sys_readahead().

POSIX_FADV_WILLNEED will generally provide asynchronous readahead semantics
for small amounts of I/O.  As long as things like indirect blocks are aready
in core.

POSIX_FADV_RANDOM gives unprivileged applications a way of disabling
readahead on a per-fd basis, which may provide some benefit for super-seeky
access patterns such as databases.



The POSIX_FADV_* values are already implemented in glibc, and this patch
ensures that they are in sync.

A test app (fadvise.c) is available in ext3 CVS.  See

	http://www.zip.com.au/~akpm/linux/ext3/

for CVS details.

Ulrich has reviewed this patch (thanks).

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/fadvise.h b/include/linux/fadvise.h
new file mode 100644
index 000000000000..6fc656dfb93d
--- /dev/null
+++ b/include/linux/fadvise.h
@@ -0,0 +1,11 @@
+#ifndef FADVISE_H_INCLUDED
+#define FADVISE_H_INCLUDED
+
+#define POSIX_FADV_NORMAL	0 /* No further special treatment.  */
+#define POSIX_FADV_RANDOM	1 /* Expect random page references.  */
+#define POSIX_FADV_SEQUENTIAL	2 /* Expect sequential page references.  */
+#define POSIX_FADV_WILLNEED	3 /* Will need these pages.  */
+#define POSIX_FADV_DONTNEED	4 /* Don't need these pages.  */
+#define POSIX_FADV_NOREUSE	5 /* Data will be accessed once.  */
+
+#endif	/* FADVISE_H_INCLUDED */