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

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Date:	Wed, 12 Dec 2012 09:33:41 +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] f2fs: fix up f2fs_get_parent issue to retrieve correct
 parent inode number

2012-12-12 (수), 00:10 +0900, Namjae Jeon:
> From: Namjae Jeon <namjae.jeon@...sung.com>
> 
> 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 and
> then initiating lookup request.
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
> Signed-off-by: Amit Sahrawat <a.sahrawat@...sung.com>
> ---
>  fs/f2fs/dir.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index b4e24f3..6cf39db 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -184,7 +184,7 @@ struct f2fs_dir_entry *f2fs_find_entry(struct inode *dir,
>  	int namelen = child->len;
>  	unsigned long npages = dir_blocks(dir);
>  	struct f2fs_dir_entry *de = NULL;
> -	f2fs_hash_t name_hash;
> +	f2fs_hash_t name_hash = 0;
>  	unsigned int max_depth;
>  	unsigned int level;
>  
> @@ -193,7 +193,8 @@ struct f2fs_dir_entry *f2fs_find_entry(struct inode *dir,
>  
>  	*res_page = NULL;
>  
> -	name_hash = f2fs_dentry_hash(name, namelen);
> +	if (strcmp(name, ".") && (strcmp(name, "..")))
> +		name_hash = f2fs_dentry_hash(name, namelen);

Got it.
For code consistency, could you rewrite the patch like below?
Thanks,

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..30ca4a2 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];
 
+	/* dot and dotdot dentries should have zero-value hash code */
+	if (!memcmp(name, ".", 1) || !memcmp(name, "..", 2))
+		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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