linux-kernel - Re: [PATCH] ocfs2/dlm: use struct

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Date:   Thu, 6 Jun 2019 06:40:00 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>
Cc:     ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ocfs2/dlm: use struct_size() helper



On 19/6/6 04:49, Gustavo A. R. Silva wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
> 
> struct dlm_migratable_lockres 
> {
> i	...
>         struct dlm_migratable_lock ml[0];  // 16 bytes each, begins at byte 112
> };
> 
> Make use of the struct_size() helper instead of an open-coded version
> in order to avoid any potential type mistakes.
> 
> So, replace the following form:
> 
> sizeof(struct dlm_migratable_lockres) + (mres->num_locks * sizeof(struct dlm_migratable_lock))
> 
> with:
> 
> struct_size(mres, ml, mres->num_locks)
> 
> Notice that, in this case, variable sz is not necessary, hence it
> is removed.
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
> ---
>  fs/ocfs2/dlm/dlmrecovery.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> index e22d6a115220..064ce5bbc3f6 100644
> --- a/fs/ocfs2/dlm/dlmrecovery.c
> +++ b/fs/ocfs2/dlm/dlmrecovery.c
> @@ -1109,7 +1109,7 @@ static int dlm_send_mig_lockres_msg(struct dlm_ctxt *dlm,
>  {
>  	u64 mig_cookie = be64_to_cpu(mres->mig_cookie);
>  	int mres_total_locks = be32_to_cpu(mres->total_locks);
> -	int sz, ret = 0, status = 0;
> +	int ret = 0, status = 0;
>  	u8 orig_flags = mres->flags,
>  	   orig_master = mres->master;
>  
> @@ -1117,9 +1117,6 @@ static int dlm_send_mig_lockres_msg(struct dlm_ctxt *dlm,
>  	if (!mres->num_locks)
>  		return 0;
>  
> -	sz = sizeof(struct dlm_migratable_lockres) +
> -		(mres->num_locks * sizeof(struct dlm_migratable_lock));
> -
>  	/* add an all-done flag if we reached the last lock */
>  	orig_flags = mres->flags;
>  	BUG_ON(total_locks > mres_total_locks);
> @@ -1133,7 +1130,8 @@ static int dlm_send_mig_lockres_msg(struct dlm_ctxt *dlm,
>  
>  	/* send it */
>  	ret = o2net_send_message(DLM_MIG_LOCKRES_MSG, dlm->key, mres,
> -				 sz, send_to, &status);
> +				 struct_size(mres, ml, mres->num_locks),
> +				 send_to, &status);
>  	if (ret < 0) {
>  		/* XXX: negative status is not handled.
>  		 * this will end up killing this node. */
>