linux-ext4 - Re: [PATCH v9 3/9] fscrypt: add functions for direct I/O support

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Date:   Fri, 23 Jul 2021 13:42:54 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Satya Tangirala <satyat@...gle.com>
Cc:     "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-kernel@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org,
        linux-block@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v9 3/9] fscrypt: add functions for direct I/O support

On Fri, Jun 04, 2021 at 09:09:02PM +0000, Satya Tangirala wrote:
> +bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
> +{
> +	const struct inode *inode = file_inode(iocb->ki_filp);
> +	const unsigned int blocksize = i_blocksize(inode);
> +
> +	/* If the file is unencrypted, no veto from us. */
> +	if (!fscrypt_needs_contents_encryption(inode))
> +		return true;
> +
> +	/* We only support direct I/O with inline crypto, not fs-layer crypto */
> +	if (!fscrypt_inode_uses_inline_crypto(inode))
> +		return false;
> +
> +	/*
> +	 * Since the granularity of encryption is filesystem blocks, the I/O
> +	 * must be block aligned -- not just disk sector aligned.
> +	 */
> +	if (!IS_ALIGNED(iocb->ki_pos | iov_iter_count(iter), blocksize))
> +		return false;

The above comment should make it clear that "block aligned" here intentionally
applies to just the position and total length, not to the individual data
buffers, for which only disk sector alignment is required.

- Eric