linux-kernel - [RFC PATCH 04/17] tracefs: Add ->unlink callback to tracefs_dir

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Date:   Tue,  5 Sep 2017 16:30:13 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        acme@...hat.com, kirill.shutemov@...ux.intel.com,
        Borislav Petkov <bp@...en8.de>, rric@...nel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [RFC PATCH 04/17] tracefs: Add ->unlink callback to tracefs_dir_ops

In addition to mkdir and rmdir, also allow unlink operation within the
'instances' directory if such callback is defined.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
---
 fs/tracefs/inode.c      | 36 +++++++++++++++++++++++++++++++++++-
 include/linux/tracefs.h |  3 ++-
 kernel/trace/trace.c    |  8 +++++++-
 3 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index b14f03a655..fba5a0ce07 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -53,6 +53,7 @@ static const struct file_operations tracefs_file_operations = {
 struct tracefs_dir_ops {
 	int (*mkdir)(const char *name);
 	int (*rmdir)(const char *name);
+	int (*unlink)(const char *name);
 };
 
 static char *get_dname(struct dentry *dentry)
@@ -124,10 +125,41 @@ static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
 	return ret;
 }
 
+static int tracefs_syscall_unlink(struct inode *inode, struct dentry *dentry)
+{
+	struct tracefs_dir_ops *tracefs_ops = dentry->d_fsdata;
+	char *name;
+	int ret;
+
+	name = get_dname(dentry);
+	if (!name)
+		return -ENOMEM;
+
+	/*
+	 * The unlink call can call the generic functions that create
+	 * the files within the tracefs system. It is up to the individual
+	 * unlink routine to handle races.
+	 * This time we need to unlock not only the parent (inode) but
+	 * also the file that is being deleted.
+	 */
+	inode_unlock(inode);
+	inode_unlock(dentry->d_inode);
+
+	ret = tracefs_ops->unlink(name);
+
+	inode_lock_nested(inode, I_MUTEX_PARENT);
+	inode_lock(dentry->d_inode);
+
+	kfree(name);
+
+	return ret;
+}
+
 static const struct inode_operations tracefs_dir_inode_operations = {
 	.lookup		= simple_lookup,
 	.mkdir		= tracefs_syscall_mkdir,
 	.rmdir		= tracefs_syscall_rmdir,
+	.unlink		= tracefs_syscall_unlink,
 };
 
 static struct inode *tracefs_get_inode(struct super_block *sb)
@@ -485,7 +517,8 @@ struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
  */
 struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
 					  int (*mkdir)(const char *name),
-					  int (*rmdir)(const char *name))
+					  int (*rmdir)(const char *name),
+					  int (*unlink)(const char *name))
 {
 	struct tracefs_dir_ops *tracefs_ops = parent ? parent->d_fsdata : NULL;
 	struct dentry *dentry;
@@ -505,6 +538,7 @@ struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *pare
 
 	tracefs_ops->mkdir = mkdir;
 	tracefs_ops->rmdir = rmdir;
+	tracefs_ops->unlink = unlink;
 	dentry->d_fsdata = tracefs_ops;
 
 	return dentry;
diff --git a/include/linux/tracefs.h b/include/linux/tracefs.h
index 5b727a17be..e5bd1f01b6 100644
--- a/include/linux/tracefs.h
+++ b/include/linux/tracefs.h
@@ -36,7 +36,8 @@ void tracefs_remove_recursive(struct dentry *dentry);
 
 struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
 					   int (*mkdir)(const char *name),
-					   int (*rmdir)(const char *name));
+					   int (*rmdir)(const char *name),
+					   int (*unlink)(const char *name));
 
 bool tracefs_initialized(void);
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 44004d8aa3..b9abd2029e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7792,11 +7792,17 @@ static int instance_rmdir(const char *name)
 	return ret;
 }
 
+static int instance_unlink(const char *name)
+{
+	return -EACCES;
+}
+
 static __init void create_trace_instances(struct dentry *d_tracer)
 {
 	trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
 							 instance_mkdir,
-							 instance_rmdir);
+							 instance_rmdir,
+							 instance_unlink);
 	if (WARN_ON(!trace_instance_dir))
 		return;
 }
-- 
2.14.1