linux-kernel - Re: [PATCH v4 03/11] fs: Initial atomic write support

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Message-ID: <ZdPZvqLgwWSP1ppv@dread.disaster.area>
Date: Tue, 20 Feb 2024 09:44:14 +1100
From: Dave Chinner <david@...morbit.com>
To: John Garry <john.g.garry@...cle.com>
Cc: axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
	jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
	viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com,
	jack@...e.cz, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
	linux-scsi@...r.kernel.org, ojaswin@...ux.ibm.com,
	linux-aio@...ck.org, linux-btrfs@...r.kernel.org,
	io-uring@...r.kernel.org, nilay@...ux.ibm.com,
	ritesh.list@...il.com,
	Prasad Singamsetty <prasad.singamsetty@...cle.com>
Subject: Re: [PATCH v4 03/11] fs: Initial atomic write support

On Mon, Feb 19, 2024 at 01:01:01PM +0000, John Garry wrote:
> @@ -3523,4 +3535,26 @@ extern int vfs_fadvise(struct file *file, loff_t offset, loff_t len,
>  extern int generic_fadvise(struct file *file, loff_t offset, loff_t len,
>  			   int advice);
>  
> +static inline bool atomic_write_valid(loff_t pos, struct iov_iter *iter,
> +			   unsigned int unit_min, unsigned int unit_max)
> +{
> +	size_t len = iov_iter_count(iter);
> +
> +	if (!iter_is_ubuf(iter))
> +		return false;
> +
> +	if (len == unit_min || len == unit_max) {
> +		/* ok if exactly min or max */
> +	} else if (len < unit_min || len > unit_max) {
> +		return false;
> +	} else if (!is_power_of_2(len)) {
> +		return false;
> +	}

This doesn't need if else if else if and it doesn't need to check
for exact unit min/max matches. The exact matches require the
length to be a power of 2, so the checks are simply:

	if (len < unit_min || len > unit_max)
		return false;
	if (!is_power_of_2(len))
		return false;

> +	if (pos & (len - 1))
> +		return false;

This has typing issues - 64 bit value, 32 bit mask. probably should
use:

	if (!IS_ALIGNED(pos, len))
		return false;

-Dave.

-- 
Dave Chinner
david@...morbit.com