Re: [PATCH v3 3/7] debugfs: add support for self-protecting attribute file fops

[Julia Lawall]

On Sun, 14 Feb 2016, Nicolai Stange wrote:

> 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.
> 
> Finally, add a Coccinelle script chasing down possible candidates
> for a DEFINE_SIMPLE_ATTRIBUTE()/debugfs_create_file() to
> DEFINE_DEBUGFS_ATTRIBUTE()/debugfs_create_file_unsafe() migration.
> 
> Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
> ---
>  fs/debugfs/file.c                                  | 28 +++++++++
>  fs/debugfs/inode.c                                 | 28 +++++++++
>  include/linux/debugfs.h                            | 26 +++++++++
>  .../api/debugfs/debugfs_simple_attr.cocci          | 68 ++++++++++++++++++++++

Shouldn't the .cocci file be in a different patch, since it has a 
different maintainer?

julia

>  4 files changed, 150 insertions(+)
>  create mode 100644 scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> 
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index f638dbc..2da5fb0 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -285,6 +285,34 @@ 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,
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index 42a9b34..f95e355 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -368,6 +368,33 @@ 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)
> @@ -378,6 +405,7 @@ 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
> diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
> index 6d45ae6..c880fe9 100644
> --- a/include/linux/debugfs.h
> +++ b/include/linux/debugfs.h
> @@ -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);
>  
> @@ -183,6 +206,9 @@ static int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
>  static 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)
>  {
> diff --git a/scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci b/scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> new file mode 100644
> index 0000000..bdc418d
> --- /dev/null
> +++ b/scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> @@ -0,0 +1,68 @@
> +///
> +/// Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE
> +/// for debugfs files.
> +///
> +/// Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
> +/// imposes some significant overhead as compared to
> +/// DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().
> +///
> +// Copyright (C): 2016 Nicolai Stange
> +// Options: --no-includes
> +//
> +
> +virtual context
> +virtual patch
> +virtual org
> +virtual report
> +
> +@dsa@
> +declarer name DEFINE_SIMPLE_ATTRIBUTE;
> +identifier dsa_fops;
> +expression dsa_get, dsa_set, dsa_fmt;
> +position p;
> +@@
> +DEFINE_SIMPLE_ATTRIBUTE@p(dsa_fops, dsa_get, dsa_set, dsa_fmt);
> +
> +@dcf@
> +expression name, mode, parent, data;
> +identifier dsa.dsa_fops;
> +@@
> +debugfs_create_file(name, mode, parent, data, &dsa_fops)
> +
> +
> +@context_dsa depends on context && dcf@
> +declarer name DEFINE_DEBUGFS_ATTRIBUTE;
> +identifier dsa.dsa_fops;
> +expression dsa.dsa_get, dsa.dsa_set, dsa.dsa_fmt;
> +@@
> +* DEFINE_SIMPLE_ATTRIBUTE(dsa_fops, dsa_get, dsa_set, dsa_fmt);
> +
> +
> +@patch_dcf depends on patch expression@
> +expression name, mode, parent, data;
> +identifier dsa.dsa_fops;
> +@@
> +- debugfs_create_file(name, mode, parent, data, &dsa_fops)
> ++ debugfs_create_file_unsafe(name, mode, parent, data, &dsa_fops)
> +
> +@patch_dsa depends on patch_dcf && patch@
> +identifier dsa.dsa_fops;
> +expression dsa.dsa_get, dsa.dsa_set, dsa.dsa_fmt;
> +@@
> +- DEFINE_SIMPLE_ATTRIBUTE(dsa_fops, dsa_get, dsa_set, dsa_fmt);
> ++ DEFINE_DEBUGFS_ATTRIBUTE(dsa_fops, dsa_get, dsa_set, dsa_fmt);
> +
> +
> +@script:python depends on org && dcf@
> +fops << dsa.dsa_fops;
> +p << dsa.p;
> +@@
> +msg="%s should be defined with DEFINE_DEBUGFS_ATTRIBUTE" % (fops)
> +coccilib.org.print_todo(p[0], msg)
> +
> +@script:python depends on report && dcf@
> +fops << dsa.dsa_fops;
> +p << dsa.p;
> +@@
> +msg="WARNING: %s should be defined with DEFINE_DEBUGFS_ATTRIBUTE" % (fops)
> +coccilib.report.print_report(p[0], msg)
> -- 
> 2.7.1
> 
>