linux-kernel - Re: [PATCH] 9p: Use hashtable.h for hash

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Message-ID: <Z98q_K71xueitBeB@codewreck.org>
Date: Sun, 23 Mar 2025 06:26:20 +0900
From: asmadeus@...ewreck.org
To: Sasha Levin <sashal@...nel.org>
Cc: ericvh@...nel.org, lucho@...kov.net, linux_oss@...debyte.com,
	v9fs@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 9p: Use hashtable.h for hash_errmap

Sasha Levin wrote on Thu, Mar 20, 2025 at 10:52:00AM -0400:
> Convert hash_errmap in error.c to use the generic hashtable
> implementation from hashtable.h instead of the manual hlist_head array
> implementation.
> 
> This simplifies the code and makes it more maintainable by using the
> standard hashtable API and removes the need for manual hash table
> management.

I'm not entierly convinced this is simpler from my little island (that's
one more API to learn about vs code that doesn't look all that
different), but I guess I can see the point from an overall perspective.

I see no problem with this, I'll pick it up for -next
Note this code is not used for 9p2000l iirc so I currently don't have
any test for it :/
(but it's simple enough that I'm willing to take the risk)

Thanks,
Dominique
> 
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  net/9p/error.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/net/9p/error.c b/net/9p/error.c
> index 8da744494b683..8ba8afc91482d 100644
> --- a/net/9p/error.c
> +++ b/net/9p/error.c
> @@ -16,6 +16,7 @@
>  #include <linux/list.h>
>  #include <linux/jhash.h>
>  #include <linux/errno.h>
> +#include <linux/hashtable.h>
>  #include <net/9p/9p.h>
>  
>  /**
> @@ -33,8 +34,8 @@ struct errormap {
>  	struct hlist_node list;
>  };
>  
> -#define ERRHASHSZ		32
> -static struct hlist_head hash_errmap[ERRHASHSZ];
> +#define ERRHASH_BITS 5
> +static DEFINE_HASHTABLE(hash_errmap, ERRHASH_BITS);
>  
>  /* FixMe - reduce to a reasonable size */
>  static struct errormap errmap[] = {
> @@ -176,18 +177,14 @@ static struct errormap errmap[] = {
>  int p9_error_init(void)
>  {
>  	struct errormap *c;
> -	int bucket;
> -
> -	/* initialize hash table */
> -	for (bucket = 0; bucket < ERRHASHSZ; bucket++)
> -		INIT_HLIST_HEAD(&hash_errmap[bucket]);
> +	u32 hash;
>  
>  	/* load initial error map into hash table */
>  	for (c = errmap; c->name; c++) {
>  		c->namelen = strlen(c->name);
> -		bucket = jhash(c->name, c->namelen, 0) % ERRHASHSZ;
> +		hash = jhash(c->name, c->namelen, 0);
>  		INIT_HLIST_NODE(&c->list);
> -		hlist_add_head(&c->list, &hash_errmap[bucket]);
> +		hash_add(hash_errmap, &c->list, hash);
>  	}
>  
>  	return 1;
> @@ -205,12 +202,12 @@ int p9_errstr2errno(char *errstr, int len)
>  {
>  	int errno;
>  	struct errormap *c;
> -	int bucket;
> +	u32 hash;
>  
>  	errno = 0;
>  	c = NULL;
> -	bucket = jhash(errstr, len, 0) % ERRHASHSZ;
> -	hlist_for_each_entry(c, &hash_errmap[bucket], list) {
> +	hash = jhash(errstr, len, 0);
> +	hash_for_each_possible(hash_errmap, c, list, hash) {
>  		if (c->namelen == len && !memcmp(c->name, errstr, len)) {
>  			errno = c->val;
>  			break;

-- 
Dominique Martinet | Asmadeus