linux-kernel - Re: [PATCH v2 09/10] ext4: factor out the common checking part of all fallocate operations

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Message-ID: <20240923083122.amqnlzxj53beqtwj@quack3>
Date: Mon, 23 Sep 2024 10:31:22 +0200
From: Jan Kara <jack@...e.cz>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, tytso@....edu,
	adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 09/10] ext4: factor out the common checking part of
 all fallocate operations

On Wed 04-09-24 14:29:24, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> Now the beginning of all the five functions in ext4_fallocate() (punch
> hole, zero range, insert range, collapse range and normal fallocate) are
> almost the same, they need to hold i_rwsem and check the validity of
> input parameters, so move the holding of i_rwsem to ext4_fallocate()
> and factor out a common helper to check the input parameters can make
> the code more clear.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
...
> +static int ext4_fallocate_check(struct inode *inode, int mode,
> +				loff_t offset, loff_t len)
> +{
> +	/* Currently except punch_hole, just for extent based files. */
> +	if (!(mode & FALLOC_FL_PUNCH_HOLE) &&
> +	    !ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
> +		return -EOPNOTSUPP;
> +
> +	/*
> +	 * Insert range and collapse range works only on fs cluster size
> +	 * aligned regions.
> +	 */
> +	if (mode & (FALLOC_FL_INSERT_RANGE | FALLOC_FL_COLLAPSE_RANGE) &&
> +	    !IS_ALIGNED(offset | len, EXT4_CLUSTER_SIZE(inode->i_sb)))
> +		return -EINVAL;
> +
> +	if (mode & FALLOC_FL_INSERT_RANGE) {
> +		/* Collapse range, offset must be less than i_size */
> +		if (offset >= inode->i_size)
> +			return -EINVAL;
> +		/* Check whether the maximum file size would be exceeded */
> +		if (len > inode->i_sb->s_maxbytes - inode->i_size)
> +			return -EFBIG;
> +	} else if (mode & FALLOC_FL_COLLAPSE_RANGE) {
> +		/*
> +		 * Insert range, there is no need to overlap collapse
> +		 * range with EOF, in which case it is effectively a
> +		 * truncate operation.
> +		 */
> +		if (offset + len >= inode->i_size)
> +			return -EINVAL;
> +	}
> +
> +	return 0;
> +}

I don't think this helps. If the code is really shared, then the
factorization is good but here you have to do various checks what operation
we perform and in that case I don't think it really helps readability to
factor out checks into a common function.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR