linux-kernel - [PATCH] random: Add comment to random

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Date:	Mon, 23 Jul 2012 09:47:57 -0700
From:	Tony Luck <tony.luck@...el.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	w@....eu, ewust@...ch.edu, zakir@...ch.edu, greg@...ah.com,
	mpm@...enic.com, nadiah@...ucsd.edu, jhalderm@...ch.edu,
	tglx@...utronix.de, davem@...emloft.net,
	Theodore Ts'o <tytso@....edu>
Subject: [PATCH] random: Add comment to random_initialize()

Many platforms have per-machine instance data (serial numbers,
asset tags, etc.) squirreled away in areas that are accessed
during early system bringup. Mixing this data into the random
pools has a very high value in providing better random data,
so we should allow (and even encourage) architecture code to
call add_device_randomness() from the setup_arch() paths.

However, this limits our options for internal structure of
the random driver since random_initialize() is not called
until long after setup_arch().

Add a big fat comment to rand_initialize() spelling out
this requirement.

Suggested-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Tony Luck <tony.luck@...el.com>
---

Theodore Ts'o wrote:
> I agree.  Want to send a revised patch with the comment, and I'll drop
> it into the random.git tree?

Additional patch rather than revised (since I'm touching different
subsystems: dmi and random).

 drivers/char/random.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 9793b40..1a2dfa8 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1087,6 +1087,16 @@ static void init_std_data(struct entropy_store *r)
 	mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
 }
 
+/*
+ * Note that setup_arch() may call add_device_randomness()
+ * long before we get here. This allows seeding of the pools
+ * with some platform dependent data very early in the boot
+ * process. But it limits our options here. We must use
+ * statically allocated structures that already have all
+ * initializations complete at compile time. We should also
+ * take care not to overwrite the precious per platform data
+ * we were given.
+ */
 static int rand_initialize(void)
 {
 	init_std_data(&input_pool);
-- 
1.7.10.2.552.gaa3bb87

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