[PATCH 06/10] debugfs: implement symbolic links

Greg Kroah-Hartman
2007-02-16T23:39:51Z

From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>

debugfs: implement symbolic links

Implement a new function debugfs_create_symlink() which can be used
to create symbolic links in debugfs. This function can be useful
for people moving functionality from /proc to debugfs (e.g. the
gcov-kernel patch).

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/debugfs/file.c | 12 +++++++
fs/debugfs/inode.c | 76 ++++++++++++++++++++++++++++++++++++++++++++--
include/linux/debugfs.h | 10 ++++++
3 files changed, 94 insertions(+), 4 deletions(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 8d130cc..682f928 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -16,6 +16,7 @@
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
+#include <linux/namei.h>
#include <linux/debugfs.h>

static ssize_t default_read_file(struct file *file, char __user *buf,
@@ -44,6 +45,17 @@ const struct file_operations debugfs_file_operations = {
.open = default_open,
};

+static void *debugfs_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+ nd_set_link(nd, dentry->d_inode->i_private);
+ return NULL;
+}
+
+const struct inode_operations debugfs_link_operations = {
+ .readlink = generic_readlink,
+ .follow_link = debugfs_follow_link,
+};
+
static void debugfs_u8_set(void *data, u64 val)
{
*(u8 *)data = val;
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index c692487..9c51a9f 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -25,11 +25,13 @@
#include <linux/namei.h>
#include <linux/debugfs.h>
#include <linux/fsnotify.h>
+#include <linux/string.h>

#define DEBUGFS_MAGIC 0x64626720

/* declared over in file.c */
extern struct file_operations debugfs_file_operations;
+extern struct inode_operations debugfs_link_operations;

static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;
@@ -51,6 +53,9 @@ static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t d
case S_IFREG:
inode->i_fop = &debugfs_file_operations;
break;
+ case S_IFLNK:
+ inode->i_op = &debugfs_link_operations;
+ break;
case S_IFDIR:
inode->i_op = &simple_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
@@ -96,6 +101,12 @@ static int debugfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
return res;
}

+static int debugfs_link(struct inode *dir, struct dentry *dentry, int mode)
+{
+ mode = (mode & S_IALLUGO) | S_IFLNK;
+ return debugfs_mknod(dir, dentry, mode, 0);
+}
+
static int debugfs_create(struct inode *dir, struct dentry *dentry, int mode)
{
int res;
@@ -158,10 +169,17 @@ static int debugfs_create_by_name(const char *name, mode_t mode,
mutex_lock(&parent->d_inode->i_mutex);
*dentry = lookup_one_len(name, parent, strlen(name));
if (!IS_ERR(*dentry)) {
- if ((mode & S_IFMT) == S_IFDIR)
+ switch (mode & S_IFMT) {
+ case S_IFDIR:
error = debugfs_mkdir(parent->d_inode, *dentry, mode);
- else
+ break;
+ case S_IFLNK:
+ error = debugfs_link(parent->d_inode, *dentry, mode);
+ break;
+ default:
error = debugfs_create(parent->d_inode, *dentry, mode);
+ break;
+ }
dput(*dentry);
} else
error = PTR_ERR(*dentry);
@@ -259,6 +277,49 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
EXPORT_SYMBOL_GPL(debugfs_create_dir);

/**
+ * debugfs_create_symlink- create a symbolic link in the debugfs filesystem
+ * @name: a pointer to a string containing the name of the symbolic link to
+ * create.
+ * @parent: a pointer to the parent dentry for this symbolic link. This
+ * should be a directory dentry if set. If this paramater is NULL,
+ * then the symbolic link will be created in the root of the debugfs
+ * filesystem.
+ * @target: a pointer to a string containing the path to the target of the
+ * symbolic link.
+ *
+ * This function creates a symbolic link with the given name in debugfs that
+ * links to the given target path.
+ *
+ * This function will return a pointer to a dentry if it succeeds. This
+ * pointer must be passed to the debugfs_remove() function when the symbolic
+ * link is to be removed (no automatic cleanup happens if your module is
+ * unloaded, you are responsible here.) If an error occurs, %NULL will be
+ * returned.
+ *
+ * If debugfs is not enabled in the kernel, the value -%ENODEV will be
+ * returned. It is not wise to check for this value, but rather, check for
+ * %NULL or !%NULL instead as to eliminate the need for #ifdef in the calling
+ * code.
+ */
+struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
+ const char *target)
+{
+ struct dentry *result;
+ char *link;
+
+ link = kstrdup(target, GFP_KERNEL);
+ if (!link)
+ return NULL;
+
+ result = debugfs_create_file(name, S_IFLNK | S_IRWXUGO, parent, link,
+ NULL);
+ if (!result)
+ kfree(link);
+ return result;
+}
+EXPORT_SYMBOL_GPL(debugfs_create_symlink);
+
+/**
* debugfs_remove - removes a file or directory from the debugfs filesystem
* @dentry: a pointer to a the dentry of the file or directory to be
* removed.
@@ -287,15 +348,22 @@ void debugfs_remove(struct dentry *dentry)
if (debugfs_positive(dentry)) {
if (dentry->d_inode) {
dget(dentry);
- if (S_ISDIR(dentry->d_inode->i_mode)) {
+ switch (dentry->d_inode->i_mode & S_IFMT) {
+ case S_IFDIR:
ret = simple_rmdir(parent->d_inode, dentry);
if (ret)
printk(KERN_ERR
"DebugFS rmdir on %s failed : "
"directory not empty.\n",
dentry->d_name.name);
- } else
+ break;
+ case S_IFLNK:
+ kfree(dentry->d_inode->i_private);
+ /* fall through */
+ default:
simple_unlink(parent->d_inode, dentry);
+ break;
+ }
if (!ret)
d_delete(dentry);
dput(dentry);
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 047567d..9fa0983 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -33,6 +33,9 @@ struct dentry *debugfs_create_file(const char *name, mode_t mode,

struct dentry *debugfs_create_dir(const char *name, struct dentry *parent);

+struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
+ const char *dest);
+
void debugfs_remove(struct dentry *dentry);

struct dentry *debugfs_create_u8(const char *name, mode_t mode,
@@ -70,6 +73,13 @@ static inline struct dentry *debugfs_create_dir(const char *name,
return ERR_PTR(-ENODEV);
}

+static inline struct dentry *debugfs_create_symlink(const char *name,
+ struct dentry *parent,
+ const char *dest)
+{
+ return ERR_PTR(-ENODEV);
+}
+
static inline void debugfs_remove(struct dentry *dentry)
{ }

--
1.5.0