problem with duplicate sysfs directories and files

problem with duplicate sysfs directories and files

[Greg KH]

Hi,

I spent some time tonight trying to track down how to fix the issue of
duplicate sysfs files and/or directories.  This happens when you try to
create a kobject with the same name in the same directory.  The creation
of the second kobject will fail, but the directory will remain in sysfs.

Now I know this isn't a normal operation, but it would be good to fix
this eventually.  I traced the issue down to fs/sysfs/dir.c:create_dir()
and the check for:
	if (error && (error != -EEXIST)) {

Problem is, error is set to -EEXIST, so we don't clean up properly.  Now
I know we can't just not check for this, as if you do that error
cleanup, the original kobject's sysfs entry gets very messed up (ls -l
does not like it at all...)

But I can't seem to figure out what exactly we need to do to clean up
properly here.

Do you, or anyone else, have any pointers or ideas?

thanks,

greg k-h

Re: problem with duplicate sysfs directories and files

[Andrew Morton]

Greg KH <greg@kroah.com> wrote:
>
> Hi,
> 
> I spent some time tonight trying to track down how to fix the issue of
> duplicate sysfs files and/or directories.  This happens when you try to
> create a kobject with the same name in the same directory.  The creation
> of the second kobject will fail, but the directory will remain in sysfs.
> 
> Now I know this isn't a normal operation, but it would be good to fix
> this eventually.  I traced the issue down to fs/sysfs/dir.c:create_dir()
> and the check for:
> 	if (error && (error != -EEXIST)) {
> 
> Problem is, error is set to -EEXIST, so we don't clean up properly.  Now
> I know we can't just not check for this, as if you do that error
> cleanup, the original kobject's sysfs entry gets very messed up (ls -l
> does not like it at all...)
> 
> But I can't seem to figure out what exactly we need to do to clean up
> properly here.
> 
> Do you, or anyone else, have any pointers or ideas?
> 

Emit a loud warning and don't bother cleaning up - leave the current
behaviour as-is.  Whatever takes the least amount code and has the minimum
end-user impact, IMO.

Re: problem with duplicate sysfs directories and files

[Greg KH]

On Wed, Mar 08, 2006 at 01:02:05AM -0800, Andrew Morton wrote:
> Greg KH <greg@kroah.com> wrote:
> >
> > Hi,
> > 
> > I spent some time tonight trying to track down how to fix the issue of
> > duplicate sysfs files and/or directories.  This happens when you try to
> > create a kobject with the same name in the same directory.  The creation
> > of the second kobject will fail, but the directory will remain in sysfs.
> > 
> > Now I know this isn't a normal operation, but it would be good to fix
> > this eventually.  I traced the issue down to fs/sysfs/dir.c:create_dir()
> > and the check for:
> > 	if (error && (error != -EEXIST)) {
> > 
> > Problem is, error is set to -EEXIST, so we don't clean up properly.  Now
> > I know we can't just not check for this, as if you do that error
> > cleanup, the original kobject's sysfs entry gets very messed up (ls -l
> > does not like it at all...)
> > 
> > But I can't seem to figure out what exactly we need to do to clean up
> > properly here.
> > 
> > Do you, or anyone else, have any pointers or ideas?
> > 
> 
> Emit a loud warning and don't bother cleaning up - leave the current
> behaviour as-is.  Whatever takes the least amount code and has the minimum
> end-user impact, IMO.

Yeah, we do give a warning.  Well, we used to always do it, but now that
more people are not using kobject_register() but only kobject_add(), it
doesn't always show up...

Here's a patch that I've added to my queue that fixes the warn issue,
but it still would be nice to fix up sysfs someday.

thanks,

greg k-h


---
 lib/kobject.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--- gregkh-2.6.orig/lib/kobject.c
+++ gregkh-2.6/lib/kobject.c
@@ -194,6 +194,17 @@ int kobject_add(struct kobject * kobj)
 		unlink(kobj);
 		if (parent)
 			kobject_put(parent);
+
+		/* be noisy on error issues */
+		if (error == -EEXIST)
+			printk("kobject_add failed for %s with -EEXIST, "
+			       "don't try to register things with the "
+			       "same name in the same directory.\n",
+			       kobject_name(kobj));
+		else
+			printk("kobject_add failed for %s (%d)\n",
+			       kobject_name(kobj), error);
+		dump_stack();
 	}
 
 	return error;
@@ -207,18 +218,13 @@ int kobject_add(struct kobject * kobj)
 
 int kobject_register(struct kobject * kobj)
 {
-	int error = 0;
+	int error = -EINVAL;
 	if (kobj) {
 		kobject_init(kobj);
 		error = kobject_add(kobj);
-		if (error) {
-			printk("kobject_register failed for %s (%d)\n",
-			       kobject_name(kobj),error);
-			dump_stack();
-		} else
+		if (!error)
 			kobject_uevent(kobj, KOBJ_ADD);
-	} else
-		error = -EINVAL;
+	}
 	return error;
 }
 

Re: problem with duplicate sysfs directories and files

[Maneesh Soni]

On Tue, Mar 07, 2006 at 11:53:42PM -0800, Greg KH wrote:
> Hi,
> 
> I spent some time tonight trying to track down how to fix the issue of
> duplicate sysfs files and/or directories.  This happens when you try to
> create a kobject with the same name in the same directory.  The creation
> of the second kobject will fail, but the directory will remain in sysfs.
> 

Let me understand this. Lets say we have sysfs directory tree like 
	/sys/a/b/c
and someone is trying to create one more kobject with name "c" for the
parent kobject "b" ? 

And are you saying that though the new creation fails but the existing
directory remains in sysfs? I think failing the new creation and leaving
the exisiting directoy is ok. But there is sysfs_dirent leakage which 
does need fixing.

> Now I know this isn't a normal operation, but it would be good to fix
> this eventually.  I traced the issue down to fs/sysfs/dir.c:create_dir()
> and the check for:
> 	if (error && (error != -EEXIST)) {
> 
> Problem is, error is set to -EEXIST, so we don't clean up properly.  Now
> I know we can't just not check for this, as if you do that error
> cleanup, the original kobject's sysfs entry gets very messed up (ls -l
> does not like it at all...)
> 
> But I can't seem to figure out what exactly we need to do to clean up
> properly here.
> 
> Do you, or anyone else, have any pointers or ideas?
> 

If you are talking about the example above, to me it appears that except
a possible sysfs_dirent leakage, we are some what ok, else there would have 
been more catastrophic results because of the duplicate directory dentry/inode.

As per the current code 

static int create_dir(struct kobject * k, struct dentry * p,
                      const char * n, struct dentry ** d)
{
        int error;
        umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;

        mutex_lock(&p->d_inode->i_mutex);

        *d = lookup_one_len(n, p, strlen(n));

^^^^ lookup_one_len() will return the existing dentry corresponding to
     the last component "c" in "/sys/a/b/c" without any error. Just note
     that VFS is not going to allocate a new dentry for it. The existing
     dentry's ref count will be increased by one.

        if (!IS_ERR(*d)) {
                error = sysfs_make_dirent(p->d_fsdata, *d, k, mode, SYSFS_DIR);

^^^^ we do have problem here, a new sysfs_dirent is allocated which
     replaces the existing dentry->d_fsdata and yuk... the old sysfs_dirent
     is no more linked with the existing directory, there by leaking 
     one sysfs_dirent.


Not only for sysfs_create_dir(), I think the problem of existing sysfs_dirent
is also there with sysfs_add_file() and sysfs_add_link(). I am working on a 
patch to plug this leak.

Thanks
Maneesh


-- 
Maneesh Soni
Linux Technology Center, 
IBM India Software Labs,
Bangalore, India
email: maneesh@in.ibm.com
Phone: 91-80-51776416





o Following patch checks for existing sysfs_dirent before allocation new one.

Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>
---

 linux-2.6.16-rc5-git10-maneesh/fs/sysfs/dir.c |   17 +++++++++++++++++
 1 files changed, 17 insertions(+)

diff -puN fs/sysfs/dir.c~sysfs-check-existing-dirent fs/sysfs/dir.c
--- linux-2.6.16-rc5-git10/fs/sysfs/dir.c~sysfs-check-existing-dirent	2006-03-08 17:50:00.857712216 +0530
+++ linux-2.6.16-rc5-git10-maneesh/fs/sysfs/dir.c	2006-03-08 17:50:00.864711152 +0530
@@ -50,11 +50,28 @@ static struct sysfs_dirent * sysfs_new_d
 	return sd;
 }
 
+/**
+ * Initialise a newly allocated sysfs_dirent and attach it to
+ * the corresponding dentry if present.
+ *
+ * Return -EEXIST if there is already a sysfs element with the same name for
+ * the same parent.
+ *
+ * called with parent inode's i_mutex held
+ */
 int sysfs_make_dirent(struct sysfs_dirent * parent_sd, struct dentry * dentry,
 			void * element, umode_t mode, int type)
 {
 	struct sysfs_dirent * sd;
 
+	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+		const unsigned char * existing = sysfs_get_name(sd);
+		if (strcmp(existing, new))
+			continue;
+		else
+			return -EEXIST;
+	}
+
 	sd = sysfs_new_dirent(parent_sd, element);
 	if (!sd)
 		return -ENOMEM;
_

Re: problem with duplicate sysfs directories and files

[Greg KH]

On Thu, Mar 09, 2006 at 08:28:24AM +0530, Maneesh Soni wrote:
> On Tue, Mar 07, 2006 at 11:53:42PM -0800, Greg KH wrote:
> > Hi,
> > 
> > I spent some time tonight trying to track down how to fix the issue of
> > duplicate sysfs files and/or directories.  This happens when you try to
> > create a kobject with the same name in the same directory.  The creation
> > of the second kobject will fail, but the directory will remain in sysfs.
> > 
> 
> Let me understand this. Lets say we have sysfs directory tree like 
> 	/sys/a/b/c
> and someone is trying to create one more kobject with name "c" for the
> parent kobject "b" ? 

Yes.

> And are you saying that though the new creation fails but the existing
> directory remains in sysfs?

No.  The new creation fails, but we end up with two "c" directories
under "b".

> I think failing the new creation and leaving the exisiting directoy is
> ok.

I agree, but that's not what happens :)

> But there is sysfs_dirent leakage which does need fixing.

Yes.

> > Now I know this isn't a normal operation, but it would be good to fix
> > this eventually.  I traced the issue down to fs/sysfs/dir.c:create_dir()
> > and the check for:
> > 	if (error && (error != -EEXIST)) {
> > 
> > Problem is, error is set to -EEXIST, so we don't clean up properly.  Now
> > I know we can't just not check for this, as if you do that error
> > cleanup, the original kobject's sysfs entry gets very messed up (ls -l
> > does not like it at all...)
> > 
> > But I can't seem to figure out what exactly we need to do to clean up
> > properly here.
> > 
> > Do you, or anyone else, have any pointers or ideas?
> > 
> 
> If you are talking about the example above, to me it appears that except
> a possible sysfs_dirent leakage, we are some what ok, else there would have 
> been more catastrophic results because of the duplicate directory dentry/inode.
> 
> As per the current code 
> 
> static int create_dir(struct kobject * k, struct dentry * p,
>                       const char * n, struct dentry ** d)
> {
>         int error;
>         umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
> 
>         mutex_lock(&p->d_inode->i_mutex);
> 
>         *d = lookup_one_len(n, p, strlen(n));
> 
> ^^^^ lookup_one_len() will return the existing dentry corresponding to
>      the last component "c" in "/sys/a/b/c" without any error. Just note
>      that VFS is not going to allocate a new dentry for it. The existing
>      dentry's ref count will be increased by one.
> 
>         if (!IS_ERR(*d)) {
>                 error = sysfs_make_dirent(p->d_fsdata, *d, k, mode, SYSFS_DIR);
> 
> ^^^^ we do have problem here, a new sysfs_dirent is allocated which
>      replaces the existing dentry->d_fsdata and yuk... the old sysfs_dirent
>      is no more linked with the existing directory, there by leaking 
>      one sysfs_dirent.

Yeah, I just couldn't figure out how to clean it up properly :)

> Not only for sysfs_create_dir(), I think the problem of existing sysfs_dirent
> is also there with sysfs_add_file() and sysfs_add_link(). I am working on a 
> patch to plug this leak.

That's great, thanks.

I have a test module that shows this at:
	http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/gregkh/sysfs-test.patch
just load the 'gregkh' module and look in /sys/class/gregkh/ to see the
duplicate "gregkh1" directories.

thanks,

greg k-h

Re: problem with duplicate sysfs directories and files

[Maneesh Soni]

On Wed, Mar 08, 2006 at 09:58:16PM -0800, Greg KH wrote:

> 
> I have a test module that shows this at:
> 	http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/gregkh/sysfs-test.patch
> just load the 'gregkh' module and look in /sys/class/gregkh/ to see the
> duplicate "gregkh1" directories.
> 

Thnaks for the testcase, I could verify the following patch using this. I
don't see the duplicate "gregkh1" directories. Please queue it for post 2.6.16
if you are ok with it.


Thanks
Maneesh


o The following patch checks for existing sysfs_dirent before 
  preparing new one while creating sysfs directories and files. 



Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>
---

 linux-2.6.16-rc5-git12-maneesh/fs/sysfs/dir.c     |   30 +++++++++++++++++++++-
 linux-2.6.16-rc5-git12-maneesh/fs/sysfs/file.c    |    4 ++
 linux-2.6.16-rc5-git12-maneesh/fs/sysfs/symlink.c |    3 +-
 linux-2.6.16-rc5-git12-maneesh/fs/sysfs/sysfs.h   |    1 
 4 files changed, 35 insertions(+), 3 deletions(-)

diff -puN fs/sysfs/dir.c~sysfs-check-existing-sysfs_dirent fs/sysfs/dir.c
--- linux-2.6.16-rc5-git12/fs/sysfs/dir.c~sysfs-check-existing-sysfs_dirent	2006-03-09 19:19:22.655241008 +0530
+++ linux-2.6.16-rc5-git12-maneesh/fs/sysfs/dir.c	2006-03-09 19:38:52.735361792 +0530
@@ -50,6 +50,30 @@ static struct sysfs_dirent * sysfs_new_d
 	return sd;
 }
 
+/**
+ *
+ * Return -EEXIST if there is already a sysfs element with the same name for
+ * the same parent.
+ *
+ * called with parent inode's i_mutex held
+ */
+int is_sysfs_dirent_exist(struct sysfs_dirent * parent_sd,
+						const unsigned char * new)
+{
+	struct sysfs_dirent * sd;
+
+	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+		const unsigned char * existing = sysfs_get_name(sd);
+		if (strcmp(existing, new))
+			continue;
+		else
+			return -EEXIST;
+	}
+
+	return 0;
+}
+
+
 int sysfs_make_dirent(struct sysfs_dirent * parent_sd, struct dentry * dentry,
 			void * element, umode_t mode, int type)
 {
@@ -102,7 +126,11 @@ static int create_dir(struct kobject * k
 	mutex_lock(&p->d_inode->i_mutex);
 	*d = lookup_one_len(n, p, strlen(n));
 	if (!IS_ERR(*d)) {
-		error = sysfs_make_dirent(p->d_fsdata, *d, k, mode, SYSFS_DIR);
+ 		if (is_sysfs_dirent_exist(p->d_fsdata, n))
+  			error = -EEXIST;
+  		else
+			error = sysfs_make_dirent(p->d_fsdata, *d, k, mode,
+								SYSFS_DIR);
 		if (!error) {
 			error = sysfs_create(*d, mode, init_dir);
 			if (!error) {
diff -puN fs/sysfs/file.c~sysfs-check-existing-sysfs_dirent fs/sysfs/file.c
--- linux-2.6.16-rc5-git12/fs/sysfs/file.c~sysfs-check-existing-sysfs_dirent	2006-03-09 19:19:22.659240400 +0530
+++ linux-2.6.16-rc5-git12-maneesh/fs/sysfs/file.c	2006-03-09 19:19:22.676237816 +0530
@@ -365,7 +365,9 @@ int sysfs_add_file(struct dentry * dir, 
 	int error = 0;
 
 	mutex_lock(&dir->d_inode->i_mutex);
-	error = sysfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
+	if (!is_sysfs_dirent_exist(parent_sd, attr->name))
+		error = sysfs_make_dirent(parent_sd, NULL, (void *) attr,
+								mode, type);
 	mutex_unlock(&dir->d_inode->i_mutex);
 
 	return error;
diff -puN fs/sysfs/symlink.c~sysfs-check-existing-sysfs_dirent fs/sysfs/symlink.c
--- linux-2.6.16-rc5-git12/fs/sysfs/symlink.c~sysfs-check-existing-sysfs_dirent	2006-03-09 19:19:22.663239792 +0530
+++ linux-2.6.16-rc5-git12-maneesh/fs/sysfs/symlink.c	2006-03-09 19:19:22.677237664 +0530
@@ -87,7 +87,8 @@ int sysfs_create_link(struct kobject * k
 	BUG_ON(!kobj || !kobj->dentry || !name);
 
 	mutex_lock(&dentry->d_inode->i_mutex);
-	error = sysfs_add_link(dentry, name, target);
+	if (!is_sysfs_dirent_exist(dentry->d_fsdata, name))
+		error = sysfs_add_link(dentry, name, target);
 	mutex_unlock(&dentry->d_inode->i_mutex);
 	return error;
 }
diff -puN fs/sysfs/sysfs.h~sysfs-check-existing-sysfs_dirent fs/sysfs/sysfs.h
--- linux-2.6.16-rc5-git12/fs/sysfs/sysfs.h~sysfs-check-existing-sysfs_dirent	2006-03-09 19:19:22.666239336 +0530
+++ linux-2.6.16-rc5-git12-maneesh/fs/sysfs/sysfs.h	2006-03-09 19:28:52.404625936 +0530
@@ -5,6 +5,7 @@ extern kmem_cache_t *sysfs_dir_cachep;
 extern struct inode * sysfs_new_inode(mode_t mode, struct sysfs_dirent *);
 extern int sysfs_create(struct dentry *, int mode, int (*init)(struct inode *));
 
+extern int is_sysfs_dirent_exist(struct sysfs_dirent *, const unsigned char * );
 extern int sysfs_make_dirent(struct sysfs_dirent *, struct dentry *, void *,
 				umode_t, int);
 
_

-- 
Maneesh Soni
Linux Technology Center, 
IBM India Software Labs,
Bangalore, India
email: maneesh@in.ibm.com
Phone: 91-80-51776416

Re: problem with duplicate sysfs directories and files

[Greg KH]

On Thu, Mar 09, 2006 at 07:40:14PM +0530, Maneesh Soni wrote:
> On Wed, Mar 08, 2006 at 09:58:16PM -0800, Greg KH wrote:
> 
> > 
> > I have a test module that shows this at:
> > 	http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/gregkh/sysfs-test.patch
> > just load the 'gregkh' module and look in /sys/class/gregkh/ to see the
> > duplicate "gregkh1" directories.
> > 
> 
> Thnaks for the testcase, I could verify the following patch using this. I
> don't see the duplicate "gregkh1" directories. Please queue it for post 2.6.16
> if you are ok with it.

Looks good.  I tweaked it a bit (returned -EEXIST from functions if the
file already existed), and renamed the function to play nicer in the
global namespace.  Updated patch is below

Thanks a lot for doing this, I appreciate it.

greg k-h

-------------

>From maneesh@in.ibm.com Thu Mar  9 06:13:04 2006
Date: Thu, 9 Mar 2006 19:40:14 +0530
From: Maneesh Soni <maneesh@in.ibm.com>
To: Greg KH <greg@kroah.com>
Cc: Patrick Mochel <mochel@digitalimplant.org>
Subject: sysfs: fix problem with duplicate sysfs directories and files
Message-ID: <20060309141014.GB10667@in.ibm.com>
Content-Disposition: inline


The following patch checks for existing sysfs_dirent before
preparing new one while creating sysfs directories and files.

Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
 fs/sysfs/dir.c     |   30 +++++++++++++++++++++++++++++-
 fs/sysfs/file.c    |    6 ++++--
 fs/sysfs/symlink.c |    5 +++--
 fs/sysfs/sysfs.h   |    1 +
 4 files changed, 37 insertions(+), 5 deletions(-)

--- gregkh-2.6.orig/fs/sysfs/dir.c
+++ gregkh-2.6/fs/sysfs/dir.c
@@ -51,6 +51,30 @@ static struct sysfs_dirent * sysfs_new_d
 	return sd;
 }
 
+/**
+ *
+ * Return -EEXIST if there is already a sysfs element with the same name for
+ * the same parent.
+ *
+ * called with parent inode's i_mutex held
+ */
+int sysfs_dirent_exist(struct sysfs_dirent *parent_sd,
+			  const unsigned char *new)
+{
+	struct sysfs_dirent * sd;
+
+	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+		const unsigned char * existing = sysfs_get_name(sd);
+		if (strcmp(existing, new))
+			continue;
+		else
+			return -EEXIST;
+	}
+
+	return 0;
+}
+
+
 int sysfs_make_dirent(struct sysfs_dirent * parent_sd, struct dentry * dentry,
 			void * element, umode_t mode, int type)
 {
@@ -117,7 +141,11 @@ static int create_dir(struct kobject * k
 	mutex_lock(&p->d_inode->i_mutex);
 	*d = lookup_one_len(n, p, strlen(n));
 	if (!IS_ERR(*d)) {
-		error = sysfs_make_dirent(p->d_fsdata, *d, k, mode, SYSFS_DIR);
+ 		if (sysfs_dirent_exist(p->d_fsdata, n))
+  			error = -EEXIST;
+  		else
+			error = sysfs_make_dirent(p->d_fsdata, *d, k, mode,
+								SYSFS_DIR);
 		if (!error) {
 			error = sysfs_create(*d, mode, init_dir);
 			if (!error) {
--- gregkh-2.6.orig/fs/sysfs/file.c
+++ gregkh-2.6/fs/sysfs/file.c
@@ -450,10 +450,12 @@ int sysfs_add_file(struct dentry * dir, 
 {
 	struct sysfs_dirent * parent_sd = dir->d_fsdata;
 	umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
-	int error = 0;
+	int error = -EEXIST;
 
 	mutex_lock(&dir->d_inode->i_mutex);
-	error = sysfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
+	if (!sysfs_dirent_exist(parent_sd, attr->name))
+		error = sysfs_make_dirent(parent_sd, NULL, (void *)attr,
+					  mode, type);
 	mutex_unlock(&dir->d_inode->i_mutex);
 
 	return error;
--- gregkh-2.6.orig/fs/sysfs/symlink.c
+++ gregkh-2.6/fs/sysfs/symlink.c
@@ -82,12 +82,13 @@ exit1:
 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
 {
 	struct dentry * dentry = kobj->dentry;
-	int error = 0;
+	int error = -EEXIST;
 
 	BUG_ON(!kobj || !kobj->dentry || !name);
 
 	mutex_lock(&dentry->d_inode->i_mutex);
-	error = sysfs_add_link(dentry, name, target);
+	if (!sysfs_dirent_exist(dentry->d_fsdata, name))
+		error = sysfs_add_link(dentry, name, target);
 	mutex_unlock(&dentry->d_inode->i_mutex);
 	return error;
 }
--- gregkh-2.6.orig/fs/sysfs/sysfs.h
+++ gregkh-2.6/fs/sysfs/sysfs.h
@@ -5,6 +5,7 @@ extern kmem_cache_t *sysfs_dir_cachep;
 extern struct inode * sysfs_new_inode(mode_t mode, struct sysfs_dirent *);
 extern int sysfs_create(struct dentry *, int mode, int (*init)(struct inode *));
 
+extern int sysfs_dirent_exist(struct sysfs_dirent *, const unsigned char *);
 extern int sysfs_make_dirent(struct sysfs_dirent *, struct dentry *, void *,
 				umode_t, int);