linux-ext4 - [PATCH] ext4: use prandom_u32() instead of get_random

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Message-Id: <1383887736-6272-1-git-send-email-tytso@mit.edu>
Date:	Fri,  8 Nov 2013 00:15:36 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>
Subject: [PATCH] ext4: use prandom_u32() instead of get_random_bytes()

Many of the uses of get_random_bytes() do not actually need
cryptographically secure random numbers.  Replace those uses with a
call to prandom_u32(), which is faster and which doesn't consume
entropy from the /dev/random driver.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 fs/ext4/ialloc.c | 2 +-
 fs/ext4/mmp.c    | 2 +-
 fs/ext4/super.c  | 7 ++-----
 3 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 137193f..0ee59a6 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -432,7 +432,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
 			ext4fs_dirhash(qstr->name, qstr->len, &hinfo);
 			grp = hinfo.hash;
 		} else
-			get_random_bytes(&grp, sizeof(grp));
+			grp = prandom_u32();
 		parent_group = (unsigned)grp % ngroups;
 		for (i = 0; i < ngroups; i++) {
 			g = (parent_group + i) % ngroups;
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 214461e..04434ad 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -259,7 +259,7 @@ static unsigned int mmp_new_seq(void)
 	u32 new_seq;
 
 	do {
-		get_random_bytes(&new_seq, sizeof(u32));
+		new_seq = prandom_u32();
 	} while (new_seq > EXT4_MMP_SEQ_MAX);
 
 	return new_seq;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d3a857b..c977f4e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3068,7 +3068,6 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_li_request *elr;
-	unsigned long rnd;
 
 	elr = kzalloc(sizeof(*elr), GFP_KERNEL);
 	if (!elr)
@@ -3083,10 +3082,8 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
 	 * spread the inode table initialization requests
 	 * better.
 	 */
-	get_random_bytes(&rnd, sizeof(rnd));
-	elr->lr_next_sched = jiffies + (unsigned long)rnd %
-			     (EXT4_DEF_LI_MAX_START_DELAY * HZ);
-
+	elr->lr_next_sched = jiffies + (prandom_u32() %
+				(EXT4_DEF_LI_MAX_START_DELAY * HZ));
 	return elr;
 }
 
-- 
1.7.12.rc0.22.gcdd159b

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