linux-ext4 - Re: [PATCH v7 08/11] ext4: move inode extension/truncate code out from ->iomap

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Date:   Wed, 6 Nov 2019 08:10:59 +1100
From:   Matthew Bobrowski <mbobrowski@...browski.org>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        riteshh@...ux.ibm.com
Subject: Re: [PATCH v7 08/11] ext4: move inode extension/truncate code out
 from ->iomap_end() callback

On Tue, Nov 05, 2019 at 07:49:50AM -0800, Darrick J. Wong wrote:
> On Tue, Nov 05, 2019 at 11:01:51PM +1100, Matthew Bobrowski wrote:
> > In preparation for implementing the iomap direct I/O modifications,
> > the inode extension/truncate code needs to be moved out from the
> > ext4_iomap_end() callback. For direct I/O, if the current code
> > remained, it would behave incorrrectly. Updating the inode size prior
> > to converting unwritten extents would potentially allow a racing
> > direct I/O read to find unwritten extents before being converted
> > correctly.
> > 
> > The inode extension/truncate code now resides within a new helper
> > ext4_handle_inode_extension(). This function has been designed so that
> > it can accommodate for both DAX and direct I/O extension/truncate
> > operations.
> > 
> > Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
> > Reviewed-by: Jan Kara <jack@...e.cz>
> > Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> > ---
> >  fs/ext4/file.c  | 89 ++++++++++++++++++++++++++++++++++++++++++++++++-
> >  fs/ext4/inode.c | 48 +-------------------------
> >  2 files changed, 89 insertions(+), 48 deletions(-)
> > 
> > diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> > index 440f4c6ba4ee..ec54fec96a81 100644
> > --- a/fs/ext4/file.c
> > +++ b/fs/ext4/file.c
> > @@ -33,6 +33,7 @@
> >  #include "ext4_jbd2.h"
> >  #include "xattr.h"
> >  #include "acl.h"
> > +#include "truncate.h"
> >  
> >  static bool ext4_dio_supported(struct inode *inode)
> >  {
> > @@ -234,12 +235,95 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
> >  	return iov_iter_count(from);
> >  }
> >  
> > +static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset,
> > +					   ssize_t written, size_t count)
> > +{
> > +	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 I/O 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; thus we won't leave
> > +	 * uninitialized blocks in a file even if we didn't succeed in writing
> > +	 * as much as we intended.
> > +	 */
> > +	WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize);
> > +	if (offset + count <= EXT4_I(inode)->i_disksize) {
> > +		/*
> > +		 * We need to ensure that the inode is removed from the orphan
> > +		 * list if it has been added prematurely, due to writeback of
> > +		 * delalloc blocks.
> > +		 */
> > +		if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) {
> > +			handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
> > +
> > +			if (IS_ERR(handle)) {
> > +				ext4_orphan_del(NULL, inode);
> > +				return PTR_ERR(handle);
> > +			}
> > +
> > +			ext4_orphan_del(handle, inode);
> > +			ext4_journal_stop(handle);
> 
> I keep seeing this chunk (and the ext4_orphan_add chunk) bouncing around
> through this patchset, which causes me to wonder -- would it be useful
> to refactor these into small helpers?  Or is it really just the same two
> orphan_add/del chunks bouncing around multiple places?

No, you're right. This and the other pattern is sprayed throughout the
patchset, but also possibly throughout some of the other chunks of
EXT4 code (I think), which I haven't touched here. So, my thought
process was to actually introduce a small separate cleanup patchset
that does exactly that i.e. moves out these duplicate chunks
orphan_add/orphan_del into small helpers.

/M