linux-kernel - RE: [RFC v2] nvfs: a filesystem for persistent memory

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Date:   Mon, 11 Jan 2021 11:57:08 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mikulas Patocka' <mpatocka@...hat.com>
CC:     'Al Viro' <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "Vishal Verma" <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Ira Weiny" <ira.weiny@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Eric Sandeen <esandeen@...hat.com>,
        Dave Chinner <dchinner@...hat.com>,
        Theodore Ts'o <tytso@....edu>,
        Wang Jianchao <jianchao.wan9@...il.com>,
        "Kani, Toshi" <toshi.kani@....com>,
        "Norton, Scott J" <scott.norton@....com>,
        "Tadakamadla, Rajesh" <rajesh.tadakamadla@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: RE: [RFC v2] nvfs: a filesystem for persistent memory

From: Mikulas Patocka
> Sent: 11 January 2021 11:44
> On Mon, 11 Jan 2021, David Laight wrote:
> 
> > From: Al Viro <viro@....linux.org.uk> On Behalf Of Al Viro
> > > Sent: 10 January 2021 16:20
...
...
> > > 	while (iov_iter_count(to)) {
...
> > > 		size = copy_to_iter(to, ptr, size);
> > > 		if (unlikely(!size)) {
> > > 			r = -EFAULT;
> > > 			goto ret_r;
> > > 		}
> > >
> > > 		pos += size;
> > > 		total += size;
> > > 	} while (iov_iter_count(to));
> >
> > That isn't the best formed loop!
> >
> > 	David
> 
> I removed the second "while" statement and fixed the arguments to
> copy_to_iter - other than that, Al's function works.

The extra while is easy to write and can be difficult to spot.
I've found them looking as the object code before now!

Oh - the error return for copy_to_iter() is wrong.
It should (probably) return 'total' if it is nonzero.

	David

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