linux-kernel - Re: [PATCH v2 1/2] befs: remove unused BEFS_BT

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Date:	Sat, 6 Aug 2016 19:34:01 +0100
From:	Salah Triki <salah.triki@...il.com>
To:	Luis de Bethencourt <luisbg@....samsung.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, salah.triki@...il.com
Subject: Re: [PATCH v2 1/2] befs: remove unused BEFS_BT_MATCH

On Fri, Aug 05, 2016 at 01:41:20PM +0100, Luis de Bethencourt wrote:
> befs_btree_find(), the only caller of befs_find_key(), only cares about if
> the return from that function is BEFS_BT_MATCH or not. It never uses the
> partial match given with BEFS_BT_MATCH. Removing that return and don't set
> the value that will go unused.
> 
> Signed-off-by: Luis de Bethencourt <luisbg@....samsung.com>
> ---
> v2: fix overflow != not found
>     keep a value for the while(!leafnode()) loop to find a leaf node and exit
> 
> 
> Hi,
> 
> This is a correction. Now I understand the difference between returning
> NOT_FOUND when the key is in a full node and we have to look in the overflow.
> Compared to NOT_FOUND when the key doesn't exist.
> 
> For the former, we can set the key value to 0 and that means check the overflow.
> 
> For the latter, we need to return an existing value, even if not correct, so
> the while loop [while (!befs_leafnode(this_node))] can find a leaf, exit and
> then see it is not the correct node in the call of befs_find_next() right after
> the loop body.
> 
> This makes the code more readable than a mysterious "partial match" that
> actually means no match.
> 
> There is still an issue with the comparison of the strings in the binary
> search. About to start looking into that but wanted to send this corrected
> patch first before any of you reviewed the faulty first version.
> 
> Thanks,
> Luis
> 
>  fs/befs/befs.h  |  1 -
>  fs/befs/btree.c | 38 ++++++++++++++++----------------------
>  2 files changed, 16 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/befs/befs.h b/fs/befs/befs.h
> index c5c6cd1..faf3fac 100644
> --- a/fs/befs/befs.h
> +++ b/fs/befs/befs.h
> @@ -79,7 +79,6 @@ enum befs_err {
>  	BEFS_BT_END,
>  	BEFS_BT_EMPTY,
>  	BEFS_BT_MATCH,
> -	BEFS_BT_PARMATCH,
>  	BEFS_BT_NOT_FOUND
>  };
>  
> diff --git a/fs/befs/btree.c b/fs/befs/btree.c
> index 3f1a391..bc7efb0 100644
> --- a/fs/befs/btree.c
> +++ b/fs/befs/btree.c
> @@ -281,9 +281,9 @@ befs_btree_find(struct super_block *sb, const befs_data_stream *ds,
>  
>  	while (!befs_leafnode(this_node)) {
>  		res = befs_find_key(sb, this_node, key, &node_off);
> -		if (res == BEFS_BT_NOT_FOUND)
> +		/* if no key set, try the overflow node */
> +		if (node_off == 0)
>  			node_off = this_node->head.overflow;
> -		/* if no match, go to overflow node */
>  		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
>  			befs_error(sb, "befs_btree_find() failed to read "
>  				   "node at %llu", node_off);
> @@ -291,8 +291,7 @@ befs_btree_find(struct super_block *sb, const befs_data_stream *ds,
>  		}
>  	}
>  
> -	/* at the correct leaf node now */
> -
> +	/* at a leaf node now, check if it is correct */
>  	res = befs_find_key(sb, this_node, key, value);
>  
>  	brelse(this_node->bh);
> @@ -321,18 +320,13 @@ befs_btree_find(struct super_block *sb, const befs_data_stream *ds,
>   * @sb: Filesystem superblock
>   * @node: Node to find the key within
>   * @findkey: Keystring to search for
> - * @value: If key is found, the value stored with the key is put here
> - *
> - * finds exact match if one exists, and returns BEFS_BT_MATCH
> - * If no exact match, finds first key in node that is greater
> - * (alphabetically) than the search key and returns BEFS_BT_PARMATCH
> - * (for partial match, I guess). Can you think of something better to
> - * call it?
> + * @value: If key is found, the value stored with the key is put here.
> + *		If not, the value is returned as 0.
>   *
> - * If no key was a match or greater than the search key, return
> - * BEFS_BT_NOT_FOUND.
> + * Finds exact match if one exists, and returns BEFS_BT_MATCH.
> + * If there is no exact match, it returns BEFS_BT_NOT_FOUND.
>   *
> - * Use binary search instead of a linear.
> + * Uses binary search instead of a linear.
>   */
>  static int
>  befs_find_key(struct super_block *sb, struct befs_btree_node *node,
> @@ -355,8 +349,8 @@ befs_find_key(struct super_block *sb, struct befs_btree_node *node,
>  
>  	eq = befs_compare_strings(thiskey, keylen, findkey, findkey_len);
>  	if (eq < 0) {
> -		befs_error(sb, "<--- %s %s not found", __func__, findkey);
> -		befs_debug(sb, "<--- %s ERROR", __func__);
> +		*value = 0;
> +		befs_debug(sb, "<--- node can't contain %s", findkey);
>  		return BEFS_BT_NOT_FOUND;
>  	}
>  
> @@ -385,12 +379,12 @@ befs_find_key(struct super_block *sb, struct befs_btree_node *node,
>  		else
>  			first = mid + 1;
>  	}
> -	if (eq < 0)
> -		*value = fs64_to_cpu(sb, valarray[mid + 1]);
> -	else
> -		*value = fs64_to_cpu(sb, valarray[mid]);
> -	befs_debug(sb, "<--- %s found %s at %d", __func__, thiskey, mid);
> -	return BEFS_BT_PARMATCH;
> +
> +	/* return an existing value so caller can arrive to a leaf node */
> +	*value = fs64_to_cpu(sb, valarray[mid]);
> +	befs_error(sb, "<--- %s %s not found", __func__, findkey);
> +	befs_debug(sb, "<--- %s ERROR", __func__);
> +	return BEFS_BT_NOT_FOUND;
>  }
>  
>  /**
> -- 
> 2.5.1
> 

Hi,

> For the former, we can set the key value to 0 and that means check the overflow.

Making befs_find_tree return BEFS_BT_OVERFLOW is more readable than checking the key value.

Nacked.

Thanx,
Salah