From: Nick Piggin <npiggin@suse.de>
Subject: Re: [patch 4/5] ext2: convert to use the new truncate convention
Date: Thu, 10 Dec 2009 12:11:03 +1100
Message-ID: <20091210011103.GB9601@nick>
References: <20091208083832.GA19823@wotan.suse.de> <20091208084209.GD19823@wotan.suse.de> <20091209145713.GD7044@quack.suse.cz>
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Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org
To: Jan Kara <jack@suse.cz>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
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In-Reply-To: <20091209145713.GD7044@quack.suse.cz>
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List-Id: linux-ext4.vger.kernel.org

On Wed, Dec 09, 2009 at 03:57:13PM +0100, Jan Kara wrote:
> On Tue 08-12-09 09:42:09, Nick Piggin wrote:
> > I also have commented a possible bug in existing ext2 code, marked with XXX.
> > 
> > Cc: linux-ext4@vger.kernel.org
> > Cc: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Nick Piggin <npiggin@suse.de>
> ...
> > @@ -752,8 +764,8 @@ int __ext2_write_begin(struct file *file
> >  		loff_t pos, unsigned len, unsigned flags,
> >  		struct page **pagep, void **fsdata)
> >  {
> > -	return block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
> > -							ext2_get_block);
> > +	return block_write_begin_newtrunc(file, mapping, pos, len, flags,
> > +					pagep, fsdata, ext2_get_block);
> >  }
>   OK, but you should update the code in dir.c using __ext2_write_begin,
> shouldn't you?

To trim off blocks past i_size on failure? Yes I guess it should.
In fact, the ext2_write_failed call could just go into here I think.
I'll take a look.


> > +static int ext2_write_end(struct file *file, struct address_space *mapping,
> > +			loff_t pos, unsigned len, unsigned copied,
> > +			struct page *page, void *fsdata)
> > +{
> > +	int ret;
> > +
> > +	ret = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
> > +	if (ret < len)
> > +		ext2_write_failed(mapping, pos + len);
> > +	return ret;
> >  }
>   OK, when doing this, please also update ext2_commit_chunk in dir.c...

I think commit_chunk is OK. Because block_write_end does not fail
and the only reason for checking failure here is in case of a short
copy (which won't happen in dir.c code).

 
> > +static void ext2_truncate_blocks(struct inode *inode, loff_t offset)
> > +{
> > +	/*
> > +	 * XXX: it seems like a bug here that we don't allow
> > +	 * IS_APPEND inode to have blocks-past-i_size trimmed off.
> > +	 * review and fix this.
> > +	 *
> > +	 * Also would be nice to be able to handle IO errors and such,
> > +	 * but that's probably too much to ask.
> > +	 */
> > +	if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
> > +	    S_ISLNK(inode->i_mode)))
> > +		return;
> > +	if (ext2_inode_is_fast_symlink(inode))
> > +		return;
> > +	if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
> > +		return;
>   Yes, I'd remove IS_APPEND check from here.

Didn't want to change that in this patch, but I'm happy for someone to
fix it (and in ext3/4 etc).

The checks probably should be done at a different level anyway: by the
time that this code gets called, the pagecache is truncated and i_size
modified anyway so it seems buggy if this made any difference.