netdev - Re: [PATCH 2/5] dccp: Auto-load (when supported) CCID plugins for negotiation

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Date:	Mon, 15 Dec 2008 11:48:22 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Gerrit Renker <gerrit@....abdn.ac.uk>
Cc:	davem@...emloft.net, dccp@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/5] dccp: Auto-load (when supported) CCID plugins for
	negotiation

Em Sat, Dec 13, 2008 at 02:41:22PM +0100, Gerrit Renker escreveu:
> This adds auto-loading of CCIDs (when module loading is enabled)
> for the purpose of feature negotiation.
> 
> The problem with loading the CCIDs at the end of feature negotiation is
> that this would happen in software interrupt context. Besides, if the host
> advertises CCIDs during negotiation, it should have them ready to use, in
> case an agreeing peer wants to use it for the connection.
> 
> Signed-off-by: Gerrit Renker <gerrit@....abdn.ac.uk>
> Signed-off-by: Ian McDonald <ian.mcdonald@...di.co.nz>
> ---
>  net/dccp/ccid.h |    1 +
>  net/dccp/ccid.c |   39 +++++++++++++++++++++++++++++----------
>  net/dccp/feat.c |    5 +++++
>  3 files changed, 35 insertions(+), 10 deletions(-)
> 
> --- a/net/dccp/ccid.h
> +++ b/net/dccp/ccid.h
> @@ -108,6 +108,7 @@ extern int  ccid_get_builtin_ccids(u8 **ccid_array, u8 *array_len);
>  extern int  ccid_getsockopt_builtin_ccids(struct sock *sk, int len,
>  					  char __user *, int __user *);
>  
> +extern int    ccid_request_modules(u8 const *ccid_array, u8 array_len);
>  extern struct ccid *ccid_new(unsigned char id, struct sock *sk, int rx,
>  			     gfp_t gfp);
>  
> --- a/net/dccp/ccid.c
> +++ b/net/dccp/ccid.c
> @@ -196,22 +196,41 @@ int ccid_unregister(struct ccid_operations *ccid_ops)
>  
>  EXPORT_SYMBOL_GPL(ccid_unregister);
>  
> +/**
> + * ccid_request_module  -  Pre-load CCID module for later use
> + * This should be called only from process context (e.g. during connection
> + * setup) and is necessary for later calls to ccid_new (typically in software
> + * interrupt), so that it has the modules available when they are needed.
> + */
> +static int ccid_request_module(u8 id)
> +{
> +	if (!in_atomic()) {

Shouldn't the above be in a BUG_ON? It looks strange to simply refuse to
do that and return OK. 

> +		ccids_read_lock();
> +		if (ccids[id] == NULL) {
> +			ccids_read_unlock();
> +			return request_module("net-dccp-ccid-%d", id);
> +		}
> +		ccids_read_unlock();
> +	}
> +	return 0;
> +}
> +
> +int ccid_request_modules(u8 const *ccid_array, u8 array_len)
> +{
> +#ifdef CONFIG_MODULES
> +	while (array_len--)
> +		if (ccid_request_module(ccid_array[array_len]))
> +			return -1;
> +#endif
> +	return 0;
> +}
> +
>  struct ccid *ccid_new(unsigned char id, struct sock *sk, int rx, gfp_t gfp)
>  {
>  	struct ccid_operations *ccid_ops;
>  	struct ccid *ccid = NULL;
>  
>  	ccids_read_lock();
> -#ifdef CONFIG_MODULES
> -	if (ccids[id] == NULL) {
> -		/* We only try to load if in process context */
> -		ccids_read_unlock();
> -		if (gfp & GFP_ATOMIC)
> -			goto out;
> -		request_module("net-dccp-ccid-%d", id);
> -		ccids_read_lock();
> -	}
> -#endif
>  	ccid_ops = ccids[id];
>  	if (ccid_ops == NULL)
>  		goto out_unlock;
> --- a/net/dccp/feat.c
> +++ b/net/dccp/feat.c
> @@ -1163,6 +1163,11 @@ int dccp_feat_init(struct sock *sk)
>  	    ccid_get_builtin_ccids(&rx.val, &rx.len))
>  		return -ENOBUFS;
>  
> +	/* Pre-load all CCID modules that are going to be advertised */
> +	rc = -EUNATCH;
> +	if (ccid_request_modules(tx.val, tx.len))
> +		goto free_ccid_lists;
> +
>  	if (!dccp_feat_prefer(sysctl_dccp_feat_tx_ccid, tx.val, tx.len) ||
>  	    !dccp_feat_prefer(sysctl_dccp_feat_rx_ccid, rx.val, rx.len))
>  		goto free_ccid_lists;
> --
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