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Date: Mon, 11 Nov 2019 00:38:15 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Jan Stancek <jstancek@...hat.com>
Cc: "Darrick J. Wong" <darrick.wong@...cle.com>,
Naresh Kamboju <naresh.kamboju@...aro.org>,
LTP List <ltp@...ts.linux.it>,
Linux-Next Mailing List <linux-next@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, chrubis <chrubis@...e.cz>,
open list <linux-kernel@...r.kernel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Mark Brown <broonie@...nel.org>, Arnd Bergmann <arnd@...db.de>,
lkft-triage@...ts.linaro.org,
Christoph Hellwig <hch@...radead.org>,
linux-ext4 <linux-ext4@...r.kernel.org>,
Theodore Ts'o <tytso@....edu>
Subject: Re: LTP: diotest4.c:476: read to read-only space. returns 0: Success
On Mon, Nov 11, 2019 at 03:19:40AM -0500, Jan Stancek wrote:
> > > loff_t length,
> > > if (pad)
> > > iomap_dio_zero(dio, iomap, pos, fs_block_size -
> > > pad);
> > > }
> > > - return copied ? copied : ret;
> > > + return copied ? (loff_t) copied : ret;
> >
> > I'm a little confused on this proposed fix -- why does casting size_t
> > (aka unsigned long) to loff_t (long long) on a 32-bit system change the
> > test outcome?
>
> Ternary operator has a return type and an attempt is made to convert
> each of operands to the type of the other. So, in this case "ret"
> appears to be converted to type of "copied" first. Both have size of
> 4 bytes on 32-bit x86:
Sounds like we should use a good old if here to avoid that whole problem
spacE:
if (copied)
return copied;
return ret;
> size_t copied = 0;
> int ret = -14;
> long long actor_ret = copied ? copied : ret;
>
> On x86_64: actor_ret == -14;
> On x86 : actor_ret == 4294967282
>
> > Does this same diotest4 failure happen with XFS? I ask
> > because XFS has been using iomap for directio for ages.
>
> Yes, it fails on XFS too.
Is this a new test? If not why was this never reported? Sounds like
we should add this test case to xfstests.
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