linux-kernel - Re: [PATCH 2/6] ext4: Check for atomic writes support in write iter

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Message-ID: <87wmhwmq01.fsf@gmail.com>
Date: Fri, 25 Oct 2024 16:03:02 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: John Garry <john.g.garry@...cle.com>, linux-ext4@...r.kernel.org
Cc: Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>, "Darrick J . Wong" <djwong@...nel.org>, Christoph Hellwig <hch@...radead.org>, Ojaswin Mujoo <ojaswin@...ux.ibm.com>, Dave Chinner <david@...morbit.com>, linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/6] ext4: Check for atomic writes support in write iter

John Garry <john.g.garry@...cle.com> writes:

> On 25/10/2024 04:45, Ritesh Harjani (IBM) wrote:
>> Let's validate using generic_atomic_write_valid() in
>> ext4_file_write_iter() if the write request has IOCB_ATOMIC set.
>> 
>> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
>> ---
>>   fs/ext4/file.c | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>> 
>> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
>> index f14aed14b9cf..b06c5d34bbd2 100644
>> --- a/fs/ext4/file.c
>> +++ b/fs/ext4/file.c
>> @@ -692,6 +692,20 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>>   	if (IS_DAX(inode))
>>   		return ext4_dax_write_iter(iocb, from);
>>   #endif
>> +
>> +	if (iocb->ki_flags & IOCB_ATOMIC) {
>> +		size_t len = iov_iter_count(from);
>> +		int ret;
>> +
>> +		if (!IS_ALIGNED(len, EXT4_SB(inode->i_sb)->fs_awu_min) ||
>> +			len > EXT4_SB(inode->i_sb)->fs_awu_max)
>> +			return -EINVAL;
>
> this looks ok, but the IS_ALIGNED() check looks odd. I am not sure why 
> you don't just check that fs_awu_max >= len >= fs_awu_min
>

I guess this was just a stricter check. But we anyways have power_of_2
and other checks in generic_atomic_write_valid(). So it does not matter. 

I can change this in v2. 

Thanks!

>> +
>> +		ret = generic_atomic_write_valid(iocb, from);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>>   	if (iocb->ki_flags & IOCB_DIRECT)
>>   		return ext4_dio_write_iter(iocb, from);
>>   	else

-ritesh