linux-kernel - Re: [V9fs-developer] [PATCH 2/6] 9p: Replace the fidlist with an IDR

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Date:   Wed, 11 Jul 2018 14:40:38 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     v9fs-developer@...ts.sourceforge.net,
        Latchesar Ionkov <lucho@...kov.net>,
        Eric Van Hensbergen <ericvh@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Ron Minnich <rminnich@...dia.gov>
Subject: Re: [V9fs-developer] [PATCH 2/6] 9p: Replace the fidlist with an IDR

Matthew Wilcox wrote on Thu, Jun 28, 2018:
> diff --git a/net/9p/client.c b/net/9p/client.c
> index f8d58b0852fe..bbab82f22c20 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -908,30 +908,27 @@ static struct p9_fid *p9_fid_create(struct p9_client *clnt)
>  {
>  	int ret;
>  	struct p9_fid *fid;
> -	unsigned long flags;
>  
>  	p9_debug(P9_DEBUG_FID, "clnt %p\n", clnt);
>  	fid = kmalloc(sizeof(struct p9_fid), GFP_KERNEL);
>  	if (!fid)
>  		return NULL;
>  
> -	ret = p9_idpool_get(clnt->fidpool);
> -	if (ret < 0)
> -		goto error;
> -	fid->fid = ret;
> -
>  	memset(&fid->qid, 0, sizeof(struct p9_qid));
>  	fid->mode = -1;
>  	fid->uid = current_fsuid();
>  	fid->clnt = clnt;
>  	fid->rdir = NULL;
> -	spin_lock_irqsave(&clnt->lock, flags);
> -	list_add(&fid->flist, &clnt->fidlist);
> -	spin_unlock_irqrestore(&clnt->lock, flags);
>  
> -	return fid;
> +	idr_preload(GFP_KERNEL);
> +	spin_lock_irq(&clnt->lock);
> +	ret = idr_alloc_u32(&clnt->fids, fid, &fid->fid, UINT_MAX, GFP_NOWAIT);

There's also a P9_NOFID that we shouldn't use, so the max here should be
P9_NOFID - 1

That aside this introduces a change of behaviour that fid used to be
alloc'd linearily from 0 which no longer holds true, that breaks one
serveur (nfs-ganesha just returns ERANGE) but others seem to handle this
just fine so they'll just need to fix that server.
max aside this looks good.

-- 
Dominique Martinet