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Message-ID: <8760xskrar.fsf@gmail.com>
Date: Sun, 14 Feb 2016 02:35:08 +0100
From: Nicolai Stange <nicstange@...il.com>
To: Nicolai Stange <nicstange@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Jonathan Corbet <corbet@....net>, Jan Kara <jack@...e.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Julia Lawall <Julia.Lawall@...6.fr>,
Gilles Muller <Gilles.Muller@...6.fr>,
Nicolas Palix <nicolas.palix@...g.fr>,
Michal Marek <mmarek@...e.com>, linux-kernel@...r.kernel.org,
cocci@...teme.lip6.fr
Subject: [PATCH v3 3/7] 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.
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@...il.com>
---
fs/debugfs/file.c | 28 +++++++++
fs/debugfs/inode.c | 28 +++++++++
include/linux/debugfs.h | 26 +++++++++
.../api/debugfs/debugfs_simple_attr.cocci | 68 ++++++++++++++++++++++
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)
+
+
+@...text_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);
+
+
+@...ch_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)
+
+@...ch_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);
+
+
+@...ipt: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)
+
+@...ipt: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
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