linux-kernel - [GFS2] Add a comment about reading the super block [69/70]

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Date:	Thu, 30 Nov 2006 12:24:05 +0000
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	cluster-devel@...hat.com, linux-kernel@...r.kernel.org
Cc:	Srinivasa Ds <srinivasa@...ibm.com>, Andrew Morton <akpm@...l.org>
Subject: [GFS2] Add a comment about reading the super block [69/70]

>>From aac1a3c77a46c2d06f297641760dd740ac2a84af Mon Sep 17 00:00:00 2001
From: Steven Whitehouse <swhiteho@...hat.com>
Date: Thu, 30 Nov 2006 10:02:19 -0500
Subject: [PATCH] [GFS2] Add a comment about reading the super block

The comment explains why we use the bio functions to read
the super block.

Signed-off-by: Steven Whitehouse <swhiteho@...hat.com>
Cc: Andrew Morton <akpm@...l.org>
Cc: Srinivasa Ds <srinivasa@...ibm.com>
---
 fs/gfs2/super.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 3b22727..43a24f2 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -180,6 +180,24 @@ static int end_bio_io_page(struct bio *b
 	return 0;
 }
 
+/**
+ * gfs2_read_super - Read the gfs2 super block from disk
+ * @sb: The VFS super block
+ * @sector: The location of the super block
+ *
+ * This uses the bio functions to read the super block from disk
+ * because we want to be 100% sure that we never read cached data.
+ * A super block is read twice only during each GFS2 mount and is
+ * never written to by the filesystem. The first time its read no
+ * locks are held, and the only details which are looked at are those
+ * relating to the locking protocol. Once locking is up and working,
+ * the sb is read again under the lock to establish the location of
+ * the master directory (contains pointers to journals etc) and the
+ * root directory.
+ *
+ * Returns: A page containing the sb or NULL
+ */
+
 struct page *gfs2_read_super(struct super_block *sb, sector_t sector)
 {
 	struct page *page;
-- 
1.4.1



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