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

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Date:   Mon, 12 Dec 2022 00:56:10 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
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 domenica 11 dicembre 2022 23:29:31 CET Al Viro wrote:
> 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?
> 
Yes, I'm sorry for these kinds of silly mistakes because while I was expecting 
to err on much more difficult topics I overlooked what I know pretty well  :-(

Shouldn't it be "return page_address(*page)" because of "page" being a pointer 
to pointer to "struct page"? Am I overlooking something?

However, the greater mistake was about doing the decomposition into three 
patches starting from the old single thing. I think that I had to start from 
scratch. I made the process the other way round. 
>
> >  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...
>
I'll send next version within tomorrow (before or after work time) because 
here it is 00.40 CET.

Thank you very much for your immediate reply.

Fabio