linux-kernel - Re: Since sysfs_mount is static and used only in sysfs_init function, it could be just an automatic variable.

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Date:	Sun, 2 Dec 2007 14:52:17 +0800
From:	"rae l" <crquan@...il.com>
To:	"Greg KH" <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Since sysfs_mount is static and used only in sysfs_init function, it could be just an automatic variable.

On Dec 2, 2007 12:48 PM, Greg KH <gregkh@...e.de> wrote:
...
> > and where is a detailed explaination on kern_mount? could someone give
> > some comments or documentation pointers on this?
>
> See the patches that Eric Biederman just posted to lkml for why this
> structure is a static pointer this way right now, it's in preparation
> for future patches.
I have checked commit 7d0c7d676cc066413e1583b5af9fba8011972d41 by Eric
W. Biederman,
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7d0c7d676cc066413e1583b5af9fba8011972d41

which just make sysfs_mount from externally visible to static that
could be only used in one c file,

but I mean that the static variable is still on kernel bss section,
this consumes a pointer (4 or 8 bytes) memory,

through a grep from fs/sysfs/, it appears that the variable
sysfs_mount is only used in the sysfs_init function,

$ grep -RsInw sysfs_mount fs/sysfs/
fs/sysfs/mount.c:25:static struct vfsmount *sysfs_mount;
fs/sysfs/mount.c:101:           sysfs_mount = kern_mount(&sysfs_fs_type);
fs/sysfs/mount.c:102:           if (IS_ERR(sysfs_mount)) {
fs/sysfs/mount.c:104:                   err = PTR_ERR(sysfs_mount);
fs/sysfs/mount.c:105:                   sysfs_mount = NULL;

we could mark this variable an automatic one, which scope is just in
this function, thus created and destroyed with the stack,
this approach does not consume a pointer on kernel bss section,

Why not do this?

-- 
Denis Cheng
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