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Date: Thu, 13 Jun 2024 08:35:53 +0100
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Subject: Re: [PATCH v4 01/22] fs: Add generic_atomic_write_valid_size()
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: axboe@kernel.dk, tytso@mit.edu, dchinner@redhat.com,
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References: <20240607143919.2622319-1-john.g.garry@oracle.com>
 <20240607143919.2622319-2-john.g.garry@oracle.com>
 <20240612211040.GJ2764752@frogsfrogsfrogs>
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From: John Garry <john.g.garry@oracle.com>
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On 12/06/2024 22:10, Darrick J. Wong wrote:
> On Fri, Jun 07, 2024 at 02:38:58PM +0000, John Garry wrote:
>> Add a generic helper for FSes to validate that an atomic write is
>> appropriately sized (along with the other checks).
>>
>> Signed-off-by: John Garry <john.g.garry@oracle.com>
>> ---
>>   include/linux/fs.h | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 069cbab62700..e13d34f8c24e 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -3645,4 +3645,16 @@ bool generic_atomic_write_valid(loff_t pos, struct iov_iter *iter)
>>   	return true;
>>   }
>>   
>> +static inline
>> +bool generic_atomic_write_valid_size(loff_t pos, struct iov_iter *iter,
>> +				unsigned int unit_min, unsigned int unit_max)
>> +{
>> +	size_t len = iov_iter_count(iter);
>> +
>> +	if (len < unit_min || len > unit_max)
>> +		return false;
>> +
>> +	return generic_atomic_write_valid(pos, iter);
>> +}
> 
> Now that I look back at "fs: Initial atomic write support" I wonder why
> not pass the iocb and the iov_iter instead of pos and the iov_iter?

The original user of generic_atomic_write_valid() 
[blkdev_dio_unaligned() or blkdev_dio_invalid() with the rename] used 
these same args, so I just went with that.

> And can these be collapsed into a single generic_atomic_write_checks()
> function?

bdev file operations would then need to use 
generic_atomic_write_valid_size(), and there is no unit_min and unit_max 
size there, apart from bdev awu min and max. And if I checked them, we 
would be duplicating checks (of awu min and max) in the block layer.

Cheers,
John