kernel: rounddown helper function

The roundup() helper function will round a given value up to a multiple of
another given value.  aka  roundup(11, 7) would give 14 = 7 * 2.  This new
function does the opposite.  It will round a given number down to the
nearest multiple of the second number: rounddown(11, 7) would give 7.

I need this in some future SELinux code and can carry the macro myself, but
figured I would put it in the core kernel so others might find and use it
if need be.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 2b0a35e6bc69..6d6eea7f7b1e 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -59,6 +59,12 @@ extern const char linux_proc_banner[];
 #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
 #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
 #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))
+#define rounddown(x, y) (                               \
+{                                                       \
+        typeof(x) __x = (x);                            \
+        __x - (__x % (y));                              \
+}                                                       \
+)
 #define DIV_ROUND_CLOSEST(x, divisor)(                  \
 {                                                       \
         typeof(divisor) __divisor = divisor;            \