linux-ext4 - Re: [PATCH v4 5/8] ext4: move inode extension/truncate code out from ->iomap

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Message-ID: <20191008112512.GH5078@quack2.suse.cz>
Date:   Tue, 8 Oct 2019 13:25:12 +0200
From:   Jan Kara <jack@...e.cz>
To:     Matthew Bobrowski <mbobrowski@...browski.org>
Cc:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v4 5/8] ext4: move inode extension/truncate code out from
 ->iomap_end() callback

On Thu 03-10-19 21:34:18, Matthew Bobrowski wrote:
> In preparation for implementing the iomap direct I/O write path
> modifications, the inode extension/truncate code needs to be moved out
> from ext4_iomap_end(). For direct I/O, if the current code remained
> within ext4_iomap_end() it would behave incorrectly. Updating the
> inode size prior to converting unwritten extents to written extents
> will potentially allow a racing direct I/O read operation to find
> unwritten extents before they've been correctly converted.
> 
> The inode extension/truncate code has been moved out into a new helper
> ext4_handle_inode_extension(). This function has been designed so that
> it can be used by both DAX and direct I/O paths.
> 
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>

Looks good to me. Fell free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

Just small nits below:

> +static int ext4_handle_inode_extension(struct inode *inode, loff_t offset,
> +				       ssize_t written, size_t count)
> +{
> +	int ret = 0;

I think both the function and callsites may be slightly simpler if you let
the function return 'written' or error (not 0 or error). But I'll leave
that decision upto you.

> +	handle_t *handle;
> +	bool truncate = false;
> +	u8 blkbits = inode->i_blkbits;
> +	ext4_lblk_t written_blk, end_blk;
> +
> +	/*
> +         * Note that EXT4_I(inode)->i_disksize can get extended up to
> +         * inode->i_size while the IO was running due to writeback of
> +         * delalloc blocks. But the code in ext4_iomap_alloc() is careful
> +         * to use zeroed / unwritten extents if this is possible and thus
> +         * we won't leave uninitialized blocks in a file even if we didn't
> +         * succeed in writing as much as we planned.
> +         */

Whitespace damaged here...

								Honza

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