linux-kernel - Re: [PATCH 2/3] fs/ufs: Change the signature of ufs_get

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Date:   Sun, 11 Dec 2022 22:29:31 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Evgeniy Dushistov <dushistov@...l.ru>,
        Ira Weiny <ira.weiny@...el.com>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] fs/ufs: Change the signature of ufs_get_page()

On Sun, Dec 11, 2022 at 10:31:10PM +0100, Fabio M. De Francesco wrote:
> -static struct page *ufs_get_page(struct inode *dir, unsigned long n)
> +static void *ufs_get_page(struct inode *dir, unsigned long n, struct page **page)
>  {
>  	struct address_space *mapping = dir->i_mapping;
> -	struct page *page = read_mapping_page(mapping, n, NULL);
> -	if (!IS_ERR(page)) {
> -		kmap(page);
> -		if (unlikely(!PageChecked(page))) {
> -			if (!ufs_check_page(page))
> +	*page = read_mapping_page(mapping, n, NULL);
> +	if (!IS_ERR(*page)) {
> +		kmap(*page);
> +		if (unlikely(!PageChecked(*page))) {
> +			if (!ufs_check_page(*page))
>  				goto fail;
>  		}
>  	}
>  	return page;

	return page_address(page), surely?
>  
>  fail:
> -	ufs_put_page(page);
> +	ufs_put_page(*page);
>  	return ERR_PTR(-EIO);
>  }
>  
> @@ -227,15 +227,12 @@ ufs_next_entry(struct super_block *sb, struct ufs_dir_entry *p)
>  
>  struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p)
>  {
> -	struct page *page = ufs_get_page(dir, 0);
> -	struct ufs_dir_entry *de = NULL;
> +	struct ufs_dir_entry *de = ufs_get_page(dir, 0, p);

... considering e.g. this.  The caller expects the pointer to beginning of
page, not pointer to struct page itself.  Other callers are also like that...