linux-kernel - Re: [PATCH v2] erofs: fix file-backed mounts over FUSE

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Message-ID: <20241114161823.GN3387508@ZenIV>
Date: Thu, 14 Nov 2024 16:18:23 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: linux-erofs@...ts.ozlabs.org, LKML <linux-kernel@...r.kernel.org>,
	syzbot+0b1279812c46e48bb0c1@...kaller.appspotmail.com
Subject: Re: [PATCH v2] erofs: fix file-backed mounts over FUSE

On Thu, Nov 14, 2024 at 05:01:09PM +0800, Gao Xiang wrote:
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -38,7 +38,9 @@ void *erofs_bread(struct erofs_buf *buf, erofs_off_t offset,
>  	}
>  	if (!folio || !folio_contains(folio, index)) {
>  		erofs_put_metabuf(buf);
> -		folio = read_mapping_folio(buf->mapping, index, NULL);
> +		folio = buf->file ? read_mapping_folio(buf->file->f_mapping,
> +					index, buf->file) :
> +			read_mapping_folio(buf->mapping, index, NULL);
>  		if (IS_ERR(folio))
>  			return folio;
>  	}
> @@ -61,8 +63,8 @@ void erofs_init_metabuf(struct erofs_buf *buf, struct super_block *sb)
>  {
>  	struct erofs_sb_info *sbi = EROFS_SB(sb);
>  
> -	if (erofs_is_fileio_mode(sbi))
> -		buf->mapping = file_inode(sbi->fdev)->i_mapping;
> +	if (erofs_is_fileio_mode(sbi))	/* some fs like FUSE needs it */
> +		buf->file = sbi->fdev;

Would be easier to set *both* ->mapping and ->file at that point, so that
erofs_bread() would just have read_mapping_folio(buf->mapping, index, buf->file),
unconditionally...