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

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Message-ID: <20241025161131.GK2386201@frogsfrogsfrogs>
Date: Fri, 25 Oct 2024 09:11:31 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Ritesh Harjani <ritesh.list@...il.com>
Cc: John Garry <john.g.garry@...cle.com>, linux-ext4@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
	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

On Fri, Oct 25, 2024 at 04:03:02PM +0530, Ritesh Harjani wrote:
> 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. 

Also please fix the weird indenting in the if test:

		if (len < EXT4_SB(inode->i_sb)->fs_awu_min) ||
		    len > EXT4_SB(inode->i_sb)->fs_awu_max)
			return -EINVAL;

--D

> 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
>