linux-ext4 - Re: [PATCH] ext3: truncate block allocated on a failed ext3_write

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Message-ID: <20080829095115.GD6447@skywalker>
Date:	Fri, 29 Aug 2008 15:21:15 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Dmitri Monakhov <dmonakhov@...nvz.org>
Cc:	cmm@...ibm.com, tytso@....edu, sandeen@...hat.com,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext3: truncate block allocated on a failed
	ext3_write_begin

On Fri, Aug 29, 2008 at 12:33:24PM +0400, Dmitri Monakhov wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:
> 
> > For blocksize < pagesize we need to remove blocks that
> > got allocte in block_wirte_begin if we fail with ENOSPC
> > for later blocks. block_write_begin internally does
> > this if it allocated page locally. This make sure
> > we don't have blocks outisde inode.i_size during
> > ENOSPC
> BTW why this check was moved from generic_XXX_write to fs speciffic code?


Not quite sure what you mean by that ? block_write_begin generic
code already does the vmtruncate if it had allocated page locally.
ext3/4 allocate/grab_cache_page  in write_begin and pass the page
pointer to block_write_begin. That implies block_write_begin
won't do the truncate. So we have to do it in filesystem write_begin.
also we have to do it after unlocking the page.


> >
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> > ---
> >  fs/ext3/inode.c |    7 +++++++
> >  1 files changed, 7 insertions(+), 0 deletions(-)
> >
> > diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
> > index ebfec4d..f8424ad 100644
> > --- a/fs/ext3/inode.c
> > +++ b/fs/ext3/inode.c
> > @@ -1186,6 +1186,13 @@ static int ext3_write_begin(struct file *file, struct address_space *mapping,
> >  		ext3_journal_stop(handle);
> >  		unlock_page(page);
> >  		page_cache_release(page);
> > +		/*
> > +		 * block_write_begin may have instantiated a few blocks
> > +		 * outside i_size.  Trim these off again. Don't need
> > +		 * i_size_read because we hold i_mutex.
> > +		 */
> > +		if (pos + len > inode->i_size)
> > +			vmtruncate(inode, inode->i_size);
> >  	}
> >  	if (ret == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))
> >  		goto retry;
> > -- 
> > 1.6.0.1.90.g27a6e
> >
> > --
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