debugfs: introduce a public file_operations accessor

This patch introduces an accessor which can be used
by the users of debugfs (drivers, fs, ...) to get the
original file_operations struct. It also removes the
REAL_FOPS_DEREF macro in file.c and converts the code
to use the public version.

Previously, REAL_FOPS_DEREF was only available within
the file.c of debugfs. But having a public getter
available for debugfs users is important as some
drivers (carl9170 and b43) use the pointer of the
original file_operations in conjunction with container_of()
within their debugfs implementations.

Reviewed-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Cc: stable <stable@vger.kernel.org> # 4.7+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 592059f88e04f7757c9e3bc413ab78bec58dee09..309f4e9b241990556311ae779baa565d1471d496 100644 (file)
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -97,9 +97,6 @@ EXPORT_SYMBOL_GPL(debugfs_use_file_finish);
 
 #define F_DENTRY(filp) ((filp)->f_path.dentry)
 
-#define REAL_FOPS_DEREF(dentry)                                        \
-       ((const struct file_operations *)(dentry)->d_fsdata)
-
 static int open_proxy_open(struct inode *inode, struct file *filp)
 {
        const struct dentry *dentry = F_DENTRY(filp);
@@ -112,7 +109,7 @@ static int open_proxy_open(struct inode *inode, struct file *filp)
                goto out;
        }
 
-       real_fops = REAL_FOPS_DEREF(dentry);
+       real_fops = debugfs_real_fops(filp);
        real_fops = fops_get(real_fops);
        if (!real_fops) {
                /* Huh? Module did not clean up after itself at exit? */
@@ -143,7 +140,7 @@ static ret_type full_proxy_ ## name(proto)                          \
 {                                                                      \
        const struct dentry *dentry = F_DENTRY(filp);                   \
        const struct file_operations *real_fops =                       \
-               REAL_FOPS_DEREF(dentry);                                \
+               debugfs_real_fops(filp);                                \
        int srcu_idx;                                                   \
        ret_type r;                                                     \
                                                                        \
@@ -176,7 +173,7 @@ static unsigned int full_proxy_poll(struct file *filp,
                                struct poll_table_struct *wait)
 {
        const struct dentry *dentry = F_DENTRY(filp);
-       const struct file_operations *real_fops = REAL_FOPS_DEREF(dentry);
+       const struct file_operations *real_fops = debugfs_real_fops(filp);
        int srcu_idx;
        unsigned int r = 0;
 
@@ -193,7 +190,7 @@ static unsigned int full_proxy_poll(struct file *filp,
 static int full_proxy_release(struct inode *inode, struct file *filp)
 {
        const struct dentry *dentry = F_DENTRY(filp);
-       const struct file_operations *real_fops = REAL_FOPS_DEREF(dentry);
+       const struct file_operations *real_fops = debugfs_real_fops(filp);
        const struct file_operations *proxy_fops = filp->f_op;
        int r = 0;
 
@@ -241,7 +238,7 @@ static int full_proxy_open(struct inode *inode, struct file *filp)
                goto out;
        }
 
-       real_fops = REAL_FOPS_DEREF(dentry);
+       real_fops = debugfs_real_fops(filp);
        real_fops = fops_get(real_fops);
        if (!real_fops) {
                /* Huh? Module did not cleanup after itself at exit? */

diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 1438e2322d5cf4f15f67db29076d013a4cd157c7..4d3f0d1aec73b856552f5d5e30b706ef5d2e04ec 100644 (file)
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -45,6 +45,23 @@ extern struct dentry *arch_debugfs_dir;
 
 extern struct srcu_struct debugfs_srcu;
 
+/**
+ * debugfs_real_fops - getter for the real file operation
+ * @filp: a pointer to a struct file
+ *
+ * Must only be called under the protection established by
+ * debugfs_use_file_start().
+ */
+static inline const struct file_operations *debugfs_real_fops(struct file *filp)
+       __must_hold(&debugfs_srcu)
+{
+       /*
+        * Neither the pointer to the struct file_operations, nor its
+        * contents ever change -- srcu_dereference() is not needed here.
+        */
+       return filp->f_path.dentry->d_fsdata;
+}
+
 #if defined(CONFIG_DEBUG_FS)
 
 struct dentry *debugfs_create_file(const char *name, umode_t mode,