linux-kernel - [RFC] fs/super.c: Why alloc_super use a static variable default

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Date:	Wed, 25 Jul 2007 11:48:35 +0800
From:	"rae l" <crquan@...il.com>
To:	"Alexander Viro" <viro@...iv.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: [RFC] fs/super.c: Why alloc_super use a static variable default_op?

Why alloc_super use a static variable default_op?
the static struct super_operations default_op is just all zeros, and
just referenced as the initial value of a new allocated super_block,
what does it for?

the filesystem dependent code such as ext2_fill_super would fill this
field eventually,
and after carefully checked, it seems no one filesystem would need a
all zero default_op,

as the command output in the kernel source tree:
$ grep -RInw s_op fs/
You could check all the use of s_op.

/**
 *	alloc_super	-	create new superblock
 *	@type:	filesystem type superblock should belong to
 *
 *	Allocates and initializes a new &struct super_block.  alloc_super()
 *	returns a pointer new superblock or %NULL if allocation had failed.
 */
static struct super_block *alloc_super(struct file_system_type *type)
{
	struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);

	static struct super_operations default_op;

	if (s) {
		...
		s->s_op = &default_op;
		s->s_time_gran = 1000000000;
	}
out:
	return s;
}

-- 
Denis Cheng
Linux Application Developer

"One of my most productive days was throwing away 1000 lines of code."
 - Ken Thompson.
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