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From: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"pali@kernel.org" <pali@kernel.org>,
	"dsterba@suse.cz" <dsterba@suse.cz>,
	"aaptel@suse.com" <aaptel@suse.com>,
	"rdunlap@infradead.org" <rdunlap@infradead.org>,
	"joe@perches.com" <joe@perches.com>,
	"mark@harmstone.com" <mark@harmstone.com>,
	"nborisov@suse.com" <nborisov@suse.com>,
	"linux-ntfs-dev@lists.sourceforge.net" 
	<linux-ntfs-dev@lists.sourceforge.net>,
	"anton@tuxera.com" <anton@tuxera.com>
Subject: RE: [PATCH v10 02/10] fs/ntfs3: Add initialization of super block
Date: Fri, 30 Oct 2020 15:54:19 +0000
Message-ID: <afb07a383dc747398f65ac541206b562@paragon-software.com> (raw)
In-Reply-To: <20201023182503.GE20115@casper.infradead.org>

From: Matthew Wilcox <willy@infradead.org>
Sent: Friday, October 23, 2020 9:25 PM
> To: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
> Cc: linux-fsdevel@vger.kernel.org; viro@zeniv.linux.org.uk; linux-kernel@vger.kernel.org; pali@kernel.org; dsterba@suse.cz;
> aaptel@suse.com; rdunlap@infradead.org; joe@perches.com; mark@harmstone.com; nborisov@suse.com; linux-ntfs-
> dev@lists.sourceforge.net; anton@tuxera.com
> Subject: Re: [PATCH v10 02/10] fs/ntfs3: Add initialization of super block
> 
> On Fri, Oct 23, 2020 at 06:44:23PM +0300, Konstantin Komarov wrote:
> > +
> > +/*ntfs_readpage*/
> > +/*ntfs_readpages*/
> > +/*ntfs_writepage*/
> > +/*ntfs_writepages*/
> > +/*ntfs_block_truncate_page*/
> 
> What are these for?
> 
> > +int ntfs_readpage(struct file *file, struct page *page)
> > +{
> > +	int err;
> > +	struct address_space *mapping = page->mapping;
> > +	struct inode *inode = mapping->host;
> > +	struct ntfs_inode *ni = ntfs_i(inode);
> > +	u64 vbo = (u64)page->index << PAGE_SHIFT;
> > +	u64 valid;
> > +	struct ATTRIB *attr;
> > +	const char *data;
> > +	u32 data_size;
> > +
> [...]
> > +
> > +	if (is_compressed(ni)) {
> > +		if (PageUptodate(page)) {
> > +			unlock_page(page);
> > +			return 0;
> > +		}
> 
> You can skip this -- the readpage op won't be called for pages which
> are Uptodate.
> 
> > +	/* normal + sparse files */
> > +	err = mpage_readpage(page, ntfs_get_block);
> > +	if (err)
> > +		goto out;
> 
> It would be nice to use iomap instead of mpage, but that's a big ask.
> 
> > +	valid = ni->i_valid;
> > +	if (vbo < valid && valid < vbo + PAGE_SIZE) {
> > +		if (PageLocked(page))
> > +			wait_on_page_bit(page, PG_locked);
> > +		if (PageError(page)) {
> > +			ntfs_inode_warn(inode, "file garbage at 0x%llx", valid);
> > +			goto out;
> > +		}
> > +		zero_user_segment(page, valid & (PAGE_SIZE - 1), PAGE_SIZE);
> 
> Nono, you can't zero data after the page has been unlocked.  You can
> handle this case in ntfs_get_block().  If the block is entirely beyond
> i_size, returning a hole will cause mpage_readpage() to zero it.  If it
> straddles i_size, you can either ensure that the on-media block contains
> zeroes after the EOF, or if you can't depend on that, you can read it
> in synchronously in your get_block() and then zero the tail and set the
> buffer Uptodate.  Not the most appetising solution, but what you have here
> is racy with the user writing to it after reading.

Hello Matthew! Thanks a lot for this feedback. Fixed in v11, please check out.

Cheers!

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-23 15:44 [PATCH v10 00/10] NTFS read-write driver GPL implementation by Paragon Software Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 01/10] fs/ntfs3: Add headers and misc files Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 02/10] fs/ntfs3: Add initialization of super block Konstantin Komarov
2020-10-23 18:25   ` Matthew Wilcox
2020-10-30 15:54     ` Konstantin Komarov [this message]
2020-10-23 15:44 ` [PATCH v10 03/10] fs/ntfs3: Add bitmap Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 04/10] fs/ntfs3: Add file operations and implementation Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 05/10] fs/ntfs3: Add attrib operations Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 06/10] fs/ntfs3: Add compression Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 07/10] fs/ntfs3: Add NTFS journal Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 08/10] fs/ntfs3: Add Kconfig, Makefile and doc Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 09/10] fs/ntfs3: Add NTFS3 in fs/Kconfig and fs/Makefile Konstantin Komarov
2020-10-23 15:44 ` [PATCH v10 10/10] fs/ntfs3: Add MAINTAINERS Konstantin Komarov

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