Commit c6468808 authored by Nicolai Stange's avatar Nicolai Stange Committed by Greg Kroah-Hartman
Browse files

debugfs: add support for self-protecting attribute file fops 



In order to protect them against file removal issues, debugfs_create_file()
creates a lifetime managing proxy around each struct file_operations
handed in.

In cases where this struct file_operations is able to manage file lifetime
by itself already, the proxy created by debugfs is a waste of resources.

The most common class of struct file_operations given to debugfs are those
defined by means of the DEFINE_SIMPLE_ATTRIBUTE() macro.

Introduce a DEFINE_DEBUGFS_ATTRIBUTE() macro to allow any
struct file_operations of this class to be easily made file lifetime aware
and thus, to be operated unproxied.

Specifically, introduce debugfs_attr_read() and debugfs_attr_write()
which wrap simple_attr_read() and simple_attr_write() under the protection
of a debugfs_use_file_start()/debugfs_use_file_finish() pair.

Make DEFINE_DEBUGFS_ATTRIBUTE() set the defined struct file_operations'
->read() and ->write() members to these wrappers.

Export debugfs_create_file_unsafe() in order to allow debugfs users to
create their files in non-proxying operation mode.

Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 49d200de

fs/debugfs/file.c

+28 −0
Original line number Diff line number Diff line
@@ -284,6 +284,34 @@ const struct file_operations debugfs_full_proxy_file_operations = { 
	.open = full_proxy_open,

};



ssize_t debugfs_attr_read(struct file *file, char __user *buf,

			size_t len, loff_t *ppos)

{

	ssize_t ret;

	int srcu_idx;



	ret = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);

	if (likely(!ret))

		ret = simple_attr_read(file, buf, len, ppos);

	debugfs_use_file_finish(srcu_idx);

	return ret;

}

EXPORT_SYMBOL_GPL(debugfs_attr_read);



ssize_t debugfs_attr_write(struct file *file, const char __user *buf,

			 size_t len, loff_t *ppos)

{

	ssize_t ret;

	int srcu_idx;



	ret = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);

	if (likely(!ret))

		ret = simple_attr_write(file, buf, len, ppos);

	debugfs_use_file_finish(srcu_idx);

	return ret;

}

EXPORT_SYMBOL_GPL(debugfs_attr_write);



static struct dentry *debugfs_create_mode(const char *name, umode_t mode,

					  struct dentry *parent, void *value,

				          const struct file_operations *fops,

fs/debugfs/inode.c

+28 −0
Original line number Diff line number Diff line
@@ -369,6 +369,33 @@ struct dentry *debugfs_create_file(const char *name, umode_t mode, 
}

EXPORT_SYMBOL_GPL(debugfs_create_file);



/**

 * debugfs_create_file_unsafe - create a file in the debugfs filesystem

 * @name: a pointer to a string containing the name of the file to create.

 * @mode: the permission that the file should have.

 * @parent: a pointer to the parent dentry for this file.  This should be a

 *          directory dentry if set.  If this parameter is NULL, then the

 *          file will be created in the root of the debugfs filesystem.

 * @data: a pointer to something that the caller will want to get to later

 *        on.  The inode.i_private pointer will point to this value on

 *        the open() call.

 * @fops: a pointer to a struct file_operations that should be used for

 *        this file.

 *

 * debugfs_create_file_unsafe() is completely analogous to

 * debugfs_create_file(), the only difference being that the fops

 * handed it will not get protected against file removals by the

 * debugfs core.

 *

 * It is your responsibility to protect your struct file_operation

 * methods against file removals by means of debugfs_use_file_start()

 * and debugfs_use_file_finish(). ->open() is still protected by

 * debugfs though.

 *

 * Any struct file_operations defined by means of

 * DEFINE_DEBUGFS_ATTRIBUTE() is protected against file removals and

 * thus, may be used here.

 */

struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,

				   struct dentry *parent, void *data,

				   const struct file_operations *fops)
@@ -379,6 +406,7 @@ struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode, 
					&debugfs_noop_file_operations,

				fops);

}

EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe);



/**

 * debugfs_create_file_size - create a file in the debugfs filesystem

include/linux/debugfs.h

+26 −0
Original line number Diff line number Diff line
@@ -50,6 +50,9 @@ extern struct srcu_struct debugfs_srcu; 
struct dentry *debugfs_create_file(const char *name, umode_t mode,

				   struct dentry *parent, void *data,

				   const struct file_operations *fops);

struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,

				   struct dentry *parent, void *data,

				   const struct file_operations *fops);



struct dentry *debugfs_create_file_size(const char *name, umode_t mode,

					struct dentry *parent, void *data,
@@ -74,6 +77,26 @@ int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx) 


void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu);



ssize_t debugfs_attr_read(struct file *file, char __user *buf,

			size_t len, loff_t *ppos);

ssize_t debugfs_attr_write(struct file *file, const char __user *buf,

			size_t len, loff_t *ppos);



#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)		\

static int __fops ## _open(struct inode *inode, struct file *file)	\

{									\

	__simple_attr_check_format(__fmt, 0ull);			\

	return simple_attr_open(inode, file, __get, __set, __fmt);	\

}									\

static const struct file_operations __fops = {				\

	.owner	 = THIS_MODULE,					\

	.open	 = __fops ## _open,					\

	.release = simple_attr_release,				\

	.read	 = debugfs_attr_read,					\

	.write	 = debugfs_attr_write,					\

	.llseek  = generic_file_llseek,				\

}



struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,

                struct dentry *new_dir, const char *new_name);
@@ -193,6 +216,9 @@ static inline void debugfs_use_file_finish(int srcu_idx) 
	__releases(&debugfs_srcu)

{ }



#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)	\

	static const struct file_operations __fops = { 0 }



static inline struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,

                struct dentry *new_dir, char *new_name)

{

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