DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=message-id:date:from:user-agent:mime-version:to:cc:subject
         :references:in-reply-to:content-type:content-transfer-encoding;
        b=Se9dQTKeGruktbAxVc16QES4zIWKoaJTcNuHZtDxlfcBLuixMtJhWV9lQV67xD/Uu+
         7dy4b9FjadgZOFbPxJk+1TmjJDEAC79o3ZPU+/2A/5x9Tq/gGmxHbvWDlO5hilNy3oG0
         Jjsa1Yh2VAi3mQ7vTGvHkxCZP8RzAQ7RpizP8=
Message-ID: <493590DA.1090504@gmail.com>
Date: Tue, 02 Dec 2008 20:47:38 +0100
From: Roel Kluin <roel.kluin@gmail.com>
User-Agent: Thunderbird 2.0.0.14 (X11/20080421)
MIME-Version: 1.0
To: Bill Davidsen <davidsen@tmr.com>
CC: Theodore Tso <tytso@mit.edu>, adilger@sun.com, linux-ext4@vger.kernel.org,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] ext3, ext4: do_split() fix loop, with obvious	unsigned
 wrap
References: <49343AD9.4020606@gmail.com> <20081202132441.GC16172@mit.edu> <49356B96.7070900@tmr.com>
In-Reply-To: <49356B96.7070900@tmr.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2179
Lines: 79

Bill Davidsen wrote:

> the value inside the loop is
> correct (or at least is the same as the original patch).

I agree, this can be shown with:

#include <stdio.h>

int main()
{
	unsigned int i, count = 10;

	printf ("The original loop:\n");
        for (i = count-1; i >= 0; i--) {
		printf ("%u, ", i);
		if (i == -1) {
			printf ("which is wrong.\n");
			break;
		}
	}

        printf ("As suggested by Bill:\n");
	for (i = count; i--; )
		printf ("%u, ", i);
	printf ("...After the loop i=%u\n");

	printf ("Your suggestion:\n");
	i = count;
	while (i--)
		printf ("%u, ", i);
	printf ("...After the loop i=%u\n");

	return 0;
}
> Theodore Tso wrote:
>> probably
>> the best way of handling this is to recast it not as a for loop, but
>> as a while loop.

Ok, with me. As also shown this will give the same results:
-----------8<--------------->8-------------
Fix loop, with obvious unsigned wrap

Signed-off-by: Roel Kluin <roel.kluin@gmail.com> 
---
diff --git a/fs/ext3/namei.c b/fs/ext3/namei.c
index 3e5edc9..0e574d4 100644
--- a/fs/ext3/namei.c
+++ b/fs/ext3/namei.c
@@ -1188,7 +1188,8 @@ static struct ext3_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
 	/* Split the existing block in the middle, size-wise */
 	size = 0;
 	move = 0;
-	for (i = count-1; i >= 0; i--) {
+	i = count;
+	while (i--) {
 		/* is more than half of this entry in 2nd half of the block? */
 		if (size + map[i].size/2 > blocksize/2)
 			break;
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 63adcb7..b8903d4 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1198,7 +1198,8 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
 	/* Split the existing block in the middle, size-wise */
 	size = 0;
 	move = 0;
-	for (i = count-1; i >= 0; i--) {
+	i = count;
+	while (i--) {
 		/* is more than half of this entry in 2nd half of the block? */
 		if (size + map[i].size/2 > blocksize/2)
 			break;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/