linux-kernel - Re: [PATCH v3] fs: Invalidate the cache for a parent block-device if fsync() is called for a partition

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Message-Id: <20120131105824.c48351b6.akpm@linux-foundation.org>
Date:	Tue, 31 Jan 2012 10:58:24 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Niels de Vos <ndevos@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	"Bryn M. Reeves" <bmr@...hat.com>
Subject: Re: [PATCH v3] fs: Invalidate the cache for a parent block-device
 if fsync() is called for a partition

On Tue, 31 Jan 2012 16:00:44 +0000
Niels de Vos <ndevos@...hat.com> wrote:

> On 01/26/2012 09:45 PM, Christoph Hellwig wrote:
> > On Thu, Jan 26, 2012 at 01:40:51PM -0800, Andrew Morton wrote:
> >> The Right Thing To Do here is to make the kernel behave logically and
> >> predictably, then modify the userspace tools.  But if we're modifying
> >> the userspace tools then we would just change userspace to issue a
> >> BLKFLSBUF to /dev/sda and leave the kernel alone.
> > 
> > The right fix is to make partition and whole disk access coherent,
> > which is fairly simply:
> > 
> >  - create the block device inode/mapping per gendisk, and only reference
> >    count it per block_device
> >  - make sure blkdev_get_block(s) applies the correct offset if used on
> >    partitions
> > 
> 
> This surely looks like a better way to fix this issue. I am not sure yet
> how much work that would involve and if I am the right person to fix
> this. If nobody beats me to it, I might send a patch for review some
> (undefined) time later.

One concern I have with the proposal is that it would forever rule out
support of >16T devices on 32-bit machines.

At present with 64-bit sector_t and 32-bit pgoff_t, I think we'd have a
reasonable chance of supporting, say, four 8T partitions on a 32T
device.  But if we were to switch the kernel from using four 4T
address_spaces (sda1-4) over to using a single 32T address_space (sda)
then we can rule it all out.

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