linux-kernel - Re: [PATCH v2] f2fs: fix up f2fs_get_parent issue to retrieve correct parent inode number

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Date:	Fri, 14 Dec 2012 13:55:21 +0900
From:	Jaegeuk Kim <jaegeuk.kim@...sung.com>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH v2] f2fs: fix up f2fs_get_parent issue to retrieve correct
 parent inode number

Hi,

> diff --git a/fs/f2fs/hash.c b/fs/f2fs/hash.c
> index a60f042..5e48bac 100644
> --- a/fs/f2fs/hash.c
> +++ b/fs/f2fs/hash.c
> @@ -76,6 +76,10 @@ f2fs_hash_t f2fs_dentry_hash(const char *name, int len)
>  	const char *p;
>  	__u32 in[8], buf[4];
>  
> +	if ((len <= 2) && (name[0] == '.') &&
> +		(name[1] == '.' || name[1] == '\0'))
> +		return 0;

If len == 1, we should avoid referencing name[1].
Likewise VFS does, I rewrote that like below.

	if (name[0] == '.') {
		switch (len) {
		case 1:
			return 0;
		case 2:
			if (name[1] == '.')
				return 0;
		}
	}

So, how about this patch?

From 391d584afadfb177584a3a3e4a7ec97e1a674457 Mon Sep 17 00:00:00 2001
From: Namjae Jeon <namjae.jeon@...sung.com>
Date: Thu, 13 Dec 2012 23:44:11 +0900
Subject: [PATCH] f2fs: fix up f2fs_get_parent issue to retrieve correct
parent
 inode number

Test Case:
[NFS Client]
ls -lR .

[NFS Server]
while [ 1 ]
do
echo 3 > /proc/sys/vm/drop_caches
done

Error on NFS Client: "No such file or directory"

When cache is dropped at the server, it results in lookup failure at the
NFS client due to non-connection with the parent. The default path is it
initiates a lookup by calculating the hash value for the name, even
though
the hash values stored on the disk for "." and ".." is maintained as
zero,
which results in failure from find_in_block due to not matching HASH
values.
Fix up, by using the correct hashing values for these entries.

Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@...sung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@...sung.com>
---
 fs/f2fs/dir.c  |  4 ++--
 fs/f2fs/hash.c | 10 ++++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index b4e24f3..e1f66df 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -540,13 +540,13 @@ int f2fs_make_empty(struct inode *inode, struct
inode *parent)
 
 	de = &dentry_blk->dentry[0];
 	de->name_len = cpu_to_le16(1);
-	de->hash_code = 0;
+	de->hash_code = f2fs_dentry_hash(".", 1);
 	de->ino = cpu_to_le32(inode->i_ino);
 	memcpy(dentry_blk->filename[0], ".", 1);
 	set_de_type(de, inode);
 
 	de = &dentry_blk->dentry[1];
-	de->hash_code = 0;
+	de->hash_code = f2fs_dentry_hash("..", 2);
 	de->name_len = cpu_to_le16(2);
 	de->ino = cpu_to_le32(parent->i_ino);
 	memcpy(dentry_blk->filename[1], "..", 2);
diff --git a/fs/f2fs/hash.c b/fs/f2fs/hash.c
index a60f042..9d7a7c6 100644
--- a/fs/f2fs/hash.c
+++ b/fs/f2fs/hash.c
@@ -76,6 +76,16 @@ f2fs_hash_t f2fs_dentry_hash(const char *name, int
len)
 	const char *p;
 	__u32 in[8], buf[4];
 
+	if (name[0] == '.') {
+		switch (len) {
+		case 1:
+			return 0;
+		case 2:
+			if (name[1] == '.')
+				return 0;
+		}
+	}
+
 	/* Initialize the default seed for the hash checksum functions */
 	buf[0] = 0x67452301;
 	buf[1] = 0xefcdab89;
-- 
1.8.0.1.250.gb7973fb

-- 
Jaegeuk Kim
Samsung

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