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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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  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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