linux-kernel - [PATCH 1/4] prandom.h: add *_state variant of prandom_u32

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Message-Id: <20201025214842.5924-2-linux@rasmusvillemoes.dk>
Date:   Sun, 25 Oct 2020 22:48:39 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Shuah Khan <shuah@...nel.org>, Kees Cook <keescook@...omium.org>
Cc:     Petr Mladek <pmladek@...e.com>, Willy Tarreau <w@....eu>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arpitha Raghunandan <98.arpi@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH 1/4] prandom.h: add *_state variant of prandom_u32_max

It is useful for test modules that make use of random numbers to allow
the exact same series of test cases to be repeated (e.g., after fixing
a bug in the code being tested). For that, the test module needs to
obtain its random numbers from a private state that can be seeded by a
known seed, e.g. given as a module parameter (and using a random seed
when that parameter is not given).

There's a few test modules I'm going to modify to follow that
scheme. As preparation, add a _state variant of the existing
prandom_u32_max(), and for convenience, also add a variant that
produces a value in a given range.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 include/linux/prandom.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/include/linux/prandom.h b/include/linux/prandom.h
index aa16e6468f91e79e1f31..58ffcd56c705be34fb98 100644
--- a/include/linux/prandom.h
+++ b/include/linux/prandom.h
@@ -46,6 +46,35 @@ static inline u32 prandom_u32_max(u32 ep_ro)
 	return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
 }
 
+/**
+ * prandom_u32_max_state - get pseudo-random number in internal [0, hi)
+ *
+ * Like prandom_u32_max, but use the given state structure.
+ * @state: pointer to state structure
+ * @hi: (exclusive) upper bound
+ *
+ * Exception: If @hi == 0, this returns 0.
+ */
+static inline u32 prandom_u32_max_state(struct rnd_state *state, u32 hi)
+{
+	return ((u64)prandom_u32_state(state) * hi) >> 32;
+}
+
+/**
+ * prandom_u32_range_state - get pseudo-random number in internal [lo, hi)
+ *
+ * @state: pointer to state structure
+ * @lo: (inclusive) lower bound
+ * @hi: (exclusive) upper bound
+ *
+ * Exception: If @lo == @hi, this returns @lo. Results are unspecified
+ * for @lo > @hi.
+ */
+static inline u32 prandom_u32_range_state(struct rnd_state *state, u32 lo, u32 hi)
+{
+	return lo + prandom_u32_max_state(state, hi - lo);
+}
+
 /*
  * Handle minimum values for seeds
  */
-- 
2.23.0