linux-kernel - Re: [PATCH v12 1/2] fs: New zonefs file system

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Date:   Fri, 7 Feb 2020 11:29:48 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Damien Le Moal <damien.lemoal@....com>
Cc:     linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Johannes Thumshirn <jth@...nel.org>,
        Naohiro Aota <naohiro.aota@....com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH v12 1/2] fs: New zonefs file system

On Thu, Feb 06, 2020 at 02:26:30PM +0900, Damien Le Moal wrote:
> zonefs is a very simple file system exposing each zone of a zoned block
> device as a file. Unlike a regular file system with zoned block device
> support (e.g. f2fs), zonefs does not hide the sequential write
> constraint of zoned block devices to the user. Files representing
> sequential write zones of the device must be written sequentially
> starting from the end of the file (append only writes).

....
> +	if (flags & IOMAP_WRITE)
> +		length = zi->i_max_size - offset;
> +	else
> +		length = min(length, isize - offset);
> +	mutex_unlock(&zi->i_truncate_mutex);
> +
> +	iomap->offset = offset & (~sbi->s_blocksize_mask);
> +	iomap->length = ((offset + length + sbi->s_blocksize_mask) &
> +			 (~sbi->s_blocksize_mask)) - iomap->offset;

	iomap->length = __ALIGN_MASK(offset + length, sbi->s_blocksize_mask) -
			iomap->offset;

or it could just use ALIGN(..., sb->s_blocksize) and not need
pre-calculation of the mask value...


> +static ssize_t zonefs_file_dio_write(struct kiocb *iocb, struct iov_iter *from)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(inode->i_sb);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	size_t count;
> +	ssize_t ret;
> +
> +	/*
> +	 * For async direct IOs to sequential zone files, ignore IOCB_NOWAIT
> +	 * as this can cause write reordering (e.g. the first aio gets EAGAIN
> +	 * on the inode lock but the second goes through but is now unaligned).
> +	 */
> +	if (zi->i_ztype == ZONEFS_ZTYPE_SEQ && !is_sync_kiocb(iocb)
> +	    && (iocb->ki_flags & IOCB_NOWAIT))
> +		iocb->ki_flags &= ~IOCB_NOWAIT;

Hmmm. I'm wondering if it would be better to return -EOPNOTSUPP here
so that the application knows it can't do non-blocking write AIO to
this file.

Everything else looks OK to me.

Cheers,

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