From: Andreas Dilger <adilger@dilger.ca>
To: Matthew Wilcox <willy@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
"Darrick J . Wong" <darrick.wong@oracle.com>,
linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 9/9] iomap: Change calling convention for zeroing
Date: Mon, 24 Aug 2020 21:35:59 -0600 [thread overview]
Message-ID: <E47B2C68-43F2-496F-AA91-A83EB3D91F28@dilger.ca> (raw)
In-Reply-To: <20200825032603.GL17456@casper.infradead.org>
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On Aug 24, 2020, at 9:26 PM, Matthew Wilcox <willy@infradead.org> wrote:
>
> On Tue, Aug 25, 2020 at 10:27:35AM +1000, Dave Chinner wrote:
>>> do {
>>> - unsigned offset, bytes;
>>> -
>>> - offset = offset_in_page(pos);
>>> - bytes = min_t(loff_t, PAGE_SIZE - offset, count);
>>> + loff_t bytes;
>>>
>>> if (IS_DAX(inode))
>>> - status = dax_iomap_zero(pos, offset, bytes, iomap);
>>> + bytes = dax_iomap_zero(pos, length, iomap);
>>
>> Hmmm. everything is loff_t here, but the callers are defining length
>> as u64, not loff_t. Is there a potential sign conversion problem
>> here? (sure 64 bit is way beyond anything we'll pass here, but...)
>
> I've gone back and forth on the correct type for 'length' a few times.
> size_t is too small (not for zeroing, but for seek()). An unsigned type
> seems right -- a length can't be negative, and we don't want to give
> the impression that it can. But the return value from these functions
> definitely needs to be signed so we can represent an error. So a u64
> length with an loff_t return type feels like the best solution. And
> the upper layers have to promise not to pass in a length that's more
> than 2^63-1.
The problem with allowing a u64 as the length is that it leads to the
possibility of an argument value that cannot be returned. Checking
length < 0 is not worse than checking length > 0x7ffffffffffffff,
and has the benefit of consistency with the other argument types and
signs...
Cheers, Andreas
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next prev parent reply other threads:[~2020-08-25 3:36 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-24 14:55 [PATCH 0/9] THP iomap patches for 5.10 Matthew Wilcox (Oracle)
2020-08-24 14:55 ` [PATCH 1/9] iomap: Fix misplaced page flushing Matthew Wilcox (Oracle)
2020-08-24 23:51 ` Dave Chinner
2020-08-25 20:47 ` Darrick J. Wong
2020-08-27 8:24 ` Christoph Hellwig
2020-08-24 14:55 ` [PATCH 2/9] fs: Introduce i_blocks_per_page Matthew Wilcox (Oracle)
2020-08-24 23:55 ` Dave Chinner
2020-08-25 20:49 ` Darrick J. Wong
2020-08-25 22:21 ` Dave Chinner
2020-08-24 14:55 ` [PATCH 3/9] iomap: Use kzalloc to allocate iomap_page Matthew Wilcox (Oracle)
2020-08-24 23:56 ` Dave Chinner
2020-08-25 20:49 ` Darrick J. Wong
2020-08-24 14:55 ` [PATCH 4/9] iomap: Use bitmap ops to set uptodate bits Matthew Wilcox (Oracle)
2020-08-24 23:56 ` Dave Chinner
2020-08-25 20:50 ` Darrick J. Wong
2020-08-24 14:55 ` [PATCH 5/9] iomap: Support arbitrarily many blocks per page Matthew Wilcox (Oracle)
2020-08-24 23:59 ` Dave Chinner
2020-08-25 0:22 ` Matthew Wilcox
2020-08-25 21:02 ` Darrick J. Wong
2020-08-26 2:26 ` Matthew Wilcox
2020-08-26 3:32 ` Darrick J. Wong
2020-08-27 8:26 ` Christoph Hellwig
2020-08-24 14:55 ` [PATCH 6/9] iomap: Convert read_count to byte count Matthew Wilcox (Oracle)
2020-08-25 0:09 ` Dave Chinner
2020-08-25 22:14 ` Darrick J. Wong
2020-08-27 8:35 ` Christoph Hellwig
2020-08-24 14:55 ` [PATCH 7/9] iomap: Convert write_count " Matthew Wilcox (Oracle)
2020-08-27 8:36 ` Christoph Hellwig
2020-08-24 14:55 ` [PATCH 8/9] iomap: Convert iomap_write_end types Matthew Wilcox (Oracle)
2020-08-25 0:12 ` Dave Chinner
2020-08-25 1:06 ` Matthew Wilcox
2020-08-25 1:33 ` Dave Chinner
2020-08-27 8:41 ` Christoph Hellwig
2020-08-24 14:55 ` [PATCH 9/9] iomap: Change calling convention for zeroing Matthew Wilcox (Oracle)
2020-08-25 0:27 ` Dave Chinner
2020-08-25 3:26 ` Matthew Wilcox
2020-08-25 3:35 ` Andreas Dilger [this message]
2020-08-25 4:27 ` Dave Chinner
2020-08-25 12:40 ` Matthew Wilcox
2020-08-25 22:05 ` Dave Chinner
2020-08-25 22:23 ` Darrick J. Wong
2020-08-27 8:39 ` Christoph Hellwig
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