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From: Chris Mason <chris.mason@oracle.com>
To: David Miller <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	btrfs-devel@oss.oracle.com
Subject: Re: [ANNOUNCE] Btrfs v0.12 released
Date: Tue, 12 Feb 2008 08:43:31 -0500	[thread overview]
Message-ID: <200802120843.31561.chris.mason@oracle.com> (raw)
In-Reply-To: <20080211.224338.07019204.davem@davemloft.net>

On Tuesday 12 February 2008, David Miller wrote:
> From: Chris Mason <chris.mason@oracle.com>
> Date: Mon, 11 Feb 2008 08:42:20 -0500
>
> > The kernel is actually worse, because the set/get macros are more
> > complex. Some live in ctree.h like in the progs, but the nasty ones live
> > in struct-funcs.c
>
> This is really problematic, because you've got these things called
> "btrfs_item_ptr()" which really isn't a pointer, it's a relative
> 'unsigned long' offset cast to a pointer.  The source of this
> seems to be btrfs_leaf_data().
>
> And then those things get passed down into the SETGET functions!

Explaining it won't make it pretty, but at least I can tell you what the code 
does.

This is all part of the btrfs code that supports tree block sizes larger than 
a page.  The extent_buffer code (extent_io.c) provides a read/write api into 
an extent_buffer based on offsets from the start of the multi-page buffer.  
That's where the relative unsigned long comes from.

The part where I cast it to pointers is me trying to maintain type checking 
throughout the code.  The pointers themselves are useless, they need to be 
matched with an extent_buffer to actually get to the bytes.

There are a few parts where the SETGET funcs are open coded, mostly in very 
performance critical functions.  Just look for lexxx_to_cpu

>
> Then deeper down we have terribly inconsistent things like
> btrfs_item_nr_offset() and
> btrfs_item_offset_nr().

Btree blocks have the offset of the item header from the start of the block 
and the offset of the item data.  And, I'm very bad at naming.

>
> Sigh... I'll see what I can do.

Thanks

-chris

  reply	other threads:[~2008-02-12 13:44 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-06 17:00 Chris Mason
2008-02-11  1:12 ` David Miller
2008-02-11 13:42   ` Chris Mason
2008-02-12  6:43     ` David Miller
2008-02-12 13:43       ` Chris Mason [this message]
2008-02-12  7:21 ` BTRFS partition usage David Miller
2008-02-12  8:11   ` David Miller
2008-02-12 13:49     ` Chris Mason
2008-02-12 14:00       ` Jan Engelhardt
2008-02-12 14:08         ` Chris Mason
2008-02-12 14:21           ` Jan Engelhardt
2008-02-12 14:35             ` Chris Mason
2008-02-12 15:04               ` Jan Engelhardt
2008-02-12 16:17                 ` Chris Mason
2008-02-12 23:38                 ` David Miller
2008-02-12 23:42                   ` Jan Engelhardt
2008-02-13  1:09                     ` David Miller
2008-02-13  1:22                     ` Rene Herman
2008-02-12 23:35               ` David Miller
2008-02-13  7:02                 ` Christoph Hellwig
2008-02-12 23:34             ` David Miller
2008-02-12 23:33           ` David Miller
2008-02-13  2:10             ` Jeff Garzik
2008-02-14  0:51               ` Szabolcs Szakacsits
2008-02-12 23:26         ` David Miller
2008-02-12 23:39           ` Jan Engelhardt
2008-02-13  1:08             ` David Miller
2008-02-13  1:25           ` Bryan Henderson
2008-02-12 23:28         ` David Miller
2008-02-13  0:45           ` Theodore Tso
2008-02-12 20:50       ` David Miller
2008-02-12  9:23 ` CRC32C big endian bugs David Miller
2008-02-12 21:55 ` BTRFS only works with PAGE_SIZE <= 4K David Miller
2008-02-12 22:03   ` Chris Mason

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