linux-kernel - Re: [PATCH 1/2] ocfs2: Use flexible array in 'struct ocfs2_recovery

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Date:   Mon, 17 Jul 2023 10:15:28 +0800
From:   Joseph Qi <jiangqi903@...il.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Mark Fasheh <mark@...heh.com>,
        Joel Becker <jlbec@...lplan.org>,
        akpm <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        ocfs2-devel@...ts.linux.dev,
        Joseph Qi <joseph.qi@...ux.alibaba.com>
Subject: Re: [PATCH 1/2] ocfs2: Use flexible array in 'struct
 ocfs2_recovery_map'



On 7/17/23 2:48 AM, Christophe JAILLET wrote:
> Turn 'rm_entries' in 'struct ocfs2_recovery_map' into a flexible array.
> 
> The advantages are:
>    - save the size of a pointer when the new undo structure is allocated
>    - avoid some always ugly pointer arithmetic to get the address of
>     'rm_entries'
>    - avoid an indirection when the array is accessed
> 
> While at it, use struct_size() to compute the size of the new undo
> structure.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>

Looks fine.
Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>


> ---
>  fs/ocfs2/journal.c | 5 +----
>  fs/ocfs2/journal.h | 2 +-
>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
> index 25d8072ccfce..2f7e70109020 100644
> --- a/fs/ocfs2/journal.c
> +++ b/fs/ocfs2/journal.c
> @@ -178,16 +178,13 @@ int ocfs2_recovery_init(struct ocfs2_super *osb)
>  	osb->recovery_thread_task = NULL;
>  	init_waitqueue_head(&osb->recovery_event);
>  
> -	rm = kzalloc(sizeof(struct ocfs2_recovery_map) +
> -		     osb->max_slots * sizeof(unsigned int),
> +	rm = kzalloc(struct_size(rm, rm_entries, osb->max_slots),
>  		     GFP_KERNEL);
>  	if (!rm) {
>  		mlog_errno(-ENOMEM);
>  		return -ENOMEM;
>  	}
>  
> -	rm->rm_entries = (unsigned int *)((char *)rm +
> -					  sizeof(struct ocfs2_recovery_map));
>  	osb->recovery_map = rm;
>  
>  	return 0;
> diff --git a/fs/ocfs2/journal.h b/fs/ocfs2/journal.h
> index 41c382f68529..41c9fe7e62f9 100644
> --- a/fs/ocfs2/journal.h
> +++ b/fs/ocfs2/journal.h
> @@ -29,7 +29,7 @@ struct ocfs2_dinode;
>  
>  struct ocfs2_recovery_map {
>  	unsigned int rm_used;
> -	unsigned int *rm_entries;
> +	unsigned int rm_entries[];
>  };
>  
>