linux-kernel - Re: [PATCH] erofs: update ctx->pos for every emitted dirent

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Date:   Sat, 28 May 2022 20:56:17 +0800
From:   Gao Xiang <xiang@...nel.org>
To:     Hongnan Li <hongnan.li@...ux.alibaba.com>
Cc:     linux-erofs@...ts.ozlabs.org, xiang@...nel.org, chao@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] erofs: update ctx->pos for every emitted dirent

Hi Hongnan,

On Fri, May 27, 2022 at 03:25:36PM +0800, Hongnan Li wrote:
> erofs_readdir update ctx->pos after filling a batch of dentries
> and it may cause dir/files duplication for NFS readdirplus which
> depends on ctx->pos to fill dir correctly. So update ctx->pos for
> every emitted dirent in erofs_fill_dentries to fix it.
> 
> Fixes: 3e917cc305c6 ("erofs: make filesystem exportable")
> Signed-off-by: Hongnan Li <hongnan.li@...ux.alibaba.com>
> ---
>  fs/erofs/dir.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
> index 18e59821c597..3015974fe2ff 100644
> --- a/fs/erofs/dir.c
> +++ b/fs/erofs/dir.c
> @@ -22,11 +22,12 @@ static void debug_one_dentry(unsigned char d_type, const char *de_name,
>  }
>  
>  static int erofs_fill_dentries(struct inode *dir, struct dir_context *ctx,
> -			       void *dentry_blk, unsigned int *ofs,
> +			       void *dentry_blk, void *dentry_begin,
>  			       unsigned int nameoff, unsigned int maxsize)
>  {
> -	struct erofs_dirent *de = dentry_blk + *ofs;
> +	struct erofs_dirent *de = dentry_begin;
>  	const struct erofs_dirent *end = dentry_blk + nameoff;
> +	loff_t begin_pos = ctx->pos;
>  
>  	while (de < end) {
>  		const char *de_name;
> @@ -59,9 +60,9 @@ static int erofs_fill_dentries(struct inode *dir, struct dir_context *ctx,
>  			/* stopped by some reason */
>  			return 1;
>  		++de;
> -		*ofs += sizeof(struct erofs_dirent);
> +		ctx->pos += sizeof(struct erofs_dirent);
>  	}
> -	*ofs = maxsize;
> +	ctx->pos = begin_pos + maxsize;
>  	return 0;
>  }
>  
> @@ -110,11 +111,9 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
>  				goto skip_this;
>  		}
>  
> -		err = erofs_fill_dentries(dir, ctx, de, &ofs,
> +		err = erofs_fill_dentries(dir, ctx, de, de + ofs,
>  					  nameoff, maxsize);

This will break the calculation, since de is a pointer of erofs_dirent
rather than byte-based.

Thanks,
Gao Xiang