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From: Christoph Hellwig <hch@infradead.org>
To: Nick Piggin <npiggin@suse.de>
Cc: Linux Filesystems <linux-fsdevel@vger.kernel.org>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [patch 2/3] fs: introduce perform_write aop
Date: Fri, 9 Mar 2007 10:39:13 +0000	[thread overview]
Message-ID: <20070309103913.GA4503@infradead.org> (raw)
In-Reply-To: <20070208105458.26443.41479.sendpatchset@linux.site>

Hi Nick,

sorry for my later reply, this has been on my to answer list for the last
month and I only managed to get back to it now.

On Thu, Feb 08, 2007 at 02:07:36PM +0100, Nick Piggin wrote:
> Add a new "perform_write" aop, which replaces prepare_write and commit_write
> as a single call to copy a given amount of userdata at the given offset. This
> is more flexible, because the implementation can determine how to best handle
> errors, or multi-page ranges (eg. it may use a gang lookup), and only requires
> one call into the fs.

I really like this idea, especially for avoiding to call into the allocator
for every block.  Have you contacted the reiser4 folks whether this would
superceed their batch_write op completely?

> One problem with this interface is that it cannot be used to write into the
> filesystem by any means other than already-initialised buffers via iovecs. So
> prepare/commit have to stay around for non-user data... 

Actually I think that's a a good thing to a certain extent.  It reminds
us that all other users are horrible abuse of the interface.  I'd even
go so far as to make batch_write a callback that the filesystem passes
to generic_file_aio_write to make clear it's not a generic thing but
a helper.  (It's not a generic thing because it's the upper layer writing
into the pagecache, not a pagecache to fs below operation).

The still leaves open on how to get rid of ->prepare_write and ->commit_write
compltely, and for that we'll probably need ->kernel_read and ->kernel_write
file operations.  But that's a step you shouldn't consider yet when doing
this work.

> Another thing is that it seems to be less able to be implemented in generic,
> reusable code. It should be possible to introduce a new 2-op interface (or
> maybe just a new error handler op) which can be used correctly in generic code.

We should be able to find a nice abstraction for this, see my next mails.

> +	/*
> +	 * perform_write replaces prepare and commit_write callbacks.
> +	 */

This is a rather useless comment :)  Better remove it and add a proper
descriptions to Documentation/filesystems/vfs.txt and
Documentation/filesystems/Locking


  reply	other threads:[~2007-03-09 10:39 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-08 13:07 [rfc][patch 0/3] a faster buffered write deadlock fix? Nick Piggin
2007-02-08 13:07 ` [patch 1/3] fs: add an iovec iterator Nick Piggin
2007-02-08 19:49   ` Christoph Hellwig
2007-02-09  1:46     ` Nick Piggin
2007-02-09  2:03       ` Nate Diller
2007-02-09  3:31         ` Nick Piggin
2007-02-09 17:28           ` Zach Brown
2007-03-09 10:40         ` Christoph Hellwig
2007-02-08 23:04   ` Mark Fasheh
2007-02-08 13:07 ` [patch 2/3] fs: introduce perform_write aop Nick Piggin
2007-03-09 10:39   ` Christoph Hellwig [this message]
2007-03-09 12:52     ` Nick Piggin
2007-03-09 22:01       ` Anton Altaparmakov
2007-03-09 23:33     ` Mark Fasheh
2007-03-10  9:25       ` Christoph Hellwig
2007-03-12  2:13         ` Mark Fasheh
2007-03-14 13:30         ` Nick Piggin
2007-03-14 15:17           ` Christoph Hellwig
2007-02-08 13:07 ` [patch 3/3] ext2: use " Nick Piggin
2007-02-08 14:47   ` Dmitriy Monakhov
2007-02-09 19:14   ` Andrew Morton
2007-02-09 19:45     ` Andrew Morton
2007-02-10  1:34       ` Nick Piggin
2007-02-10  1:50         ` Andrew Morton
2007-02-09  0:38 ` [rfc][patch 0/3] a faster buffered write deadlock fix? Mark Fasheh
2007-02-09  2:04   ` Nick Piggin
2007-02-09  8:41 ` Andrew Morton
2007-02-09  9:54   ` Nick Piggin
2007-02-09 10:09     ` Andrew Morton
2007-02-09 10:32       ` Nick Piggin
2007-02-09 10:52         ` Andrew Morton
2007-02-09 11:31           ` Nick Piggin
2007-02-09 11:46             ` Andrew Morton
2007-02-09 12:11               ` Nick Piggin

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