linux-kernel - Re: [PATCH v2 3/4] cachestat: implement cachestat syscall

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Message-ID: <Y5crEpr5QWptjK17@bfoster>
Date:   Mon, 12 Dec 2022 08:22:26 -0500
From:   Brian Foster <bfoster@...hat.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Nhat Pham <nphamcs@...il.com>, akpm@...ux-foundation.org,
        hannes@...xchg.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, willy@...radead.org,
        kernel-team@...a.com
Subject: Re: [PATCH v2 3/4] cachestat: implement cachestat syscall

On Sat, Dec 10, 2022 at 11:51:32PM +0000, Al Viro wrote:
> On Mon, Dec 05, 2022 at 09:51:39AM -0800, Nhat Pham wrote:
> 
> > +	if (!access_ok(cstat, sizeof(struct cachestat)))
> > +		return -EFAULT;
> 
> What for?  You are using copy_to_user() later, right?
> 
> > +	f = fdget(fd);
> > +	if (f.file) {
> 
> It would be easier to read if you inverted the condition here.
> 

Seconded.. I mentioned the same the last time I looked at this. On
looking again, perhaps it might even make sense to create a
filemap_cachestat() to split up the syscall bits from the associated map
walking bits..? That subsequently raises the question of whether a new
.c file is really necessary..

Brian