linux-kernel - Re: [PATCH 3/3] x86: OLPC: speed up device tree creation during boot (v2)

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Date:	Thu, 23 Dec 2010 12:57:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andres Salomon <dilinger@...ued.net>,
	Milton Miller <miltonm@....com>,
	Grant Likely <grant.likely@...retlab.ca>,
	devicetree-discuss@...ts.ozlabs.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] x86: OLPC: speed up device tree creation during boot
 (v2)


* Ingo Molnar <mingo@...e.hu> wrote:

> > However, I have to vehemently object to putting them in a wider scope
> > than is otherwise necessary.  I agree that static variables should be
> > used sparsely if at all (there really are vary few uses of them that are
> > valid), but putting them in a larger scope screams "I'm used in more
> > than one function", and that is *not* a good thing.
> 
> That's why we sometimes use the (imperfect) compromise to put them in front of 
> that function, not at the top of the file.
> 
> Look at the general balance of hardship: very little harm is done (it's not a big 
> deal if a variable is only used in a single function) but having it with local 
> variables can be _really_ harmful - for example i overlooked them when i reviewed 
> this patch. I dont like important details obscured - i like them to be apparent. 
> Again, this is something that some people can parse immediately on the visual 
> level - me and many others cannot.

As an addendum, beyond my own bad experience with them, see below a recent upstream 
fix that shows the kinds of problems that overlooked function scope statics can 
cause.

	Ingo

------------->
>From 3cb50ddf97a0a1ca4c68bc12fa1e727a6b45fbf2 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@...IV.linux.org.uk>
Date: Mon, 20 Dec 2010 15:53:18 +0000
Subject: [PATCH] Fix btrfs b0rkage

Buggered-in: 76dda93c6ae2 ("Btrfs: add snapshot/subvolume destroy
ioctl")

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Acked-by: Chris Mason <chris.mason@...cle.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
---
 fs/btrfs/export.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index 6f04444..659f532 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -166,7 +166,7 @@ static struct dentry *btrfs_fh_to_dentry(struct super_block *sb, struct fid *fh,
 static struct dentry *btrfs_get_parent(struct dentry *child)
 {
 	struct inode *dir = child->d_inode;
-	static struct dentry *dentry;
+	struct dentry *dentry;
 	struct btrfs_root *root = BTRFS_I(dir)->root;
 	struct btrfs_path *path;
 	struct extent_buffer *leaf;
--
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