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Subject[RFC PATCH 1/9] debugfs: add support for more elaborate ->d_fsdata
Date
Currently, the user provided fops, "real_fops", are stored directly into
->d_fsdata.

In order to be able to store more per-file state and thus prepare for more
granular file removal protection, wrap the real_fops into a dynamically
allocated container struct, debugfs_fsdata.

A struct debugfs_fsdata gets allocated at file creation and freed from the
newly intoduced ->d_release().

Finally, move the implementation of debugfs_real_fops() out of the public
debugfs header such that struct debugfs_fsdata's declaration can be kept
private.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
---
fs/debugfs/file.c | 12 ++++++++++++
fs/debugfs/inode.c | 22 +++++++++++++++++++---
fs/debugfs/internal.h | 4 ++++
include/linux/debugfs.h | 20 +++-----------------
4 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 354e2ab62031..15655a1a0704 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -97,6 +97,18 @@ EXPORT_SYMBOL_GPL(debugfs_use_file_finish);

#define F_DENTRY(filp) ((filp)->f_path.dentry)

+const struct file_operations *debugfs_real_fops(const struct file *filp)
+ __must_hold(&debugfs_srcu)
+{
+ struct debugfs_fsdata *fsd = F_DENTRY(filp)->d_fsdata;
+ /*
+ * Neither the pointer to the struct file_operations, nor its
+ * contents ever change -- srcu_dereference() is not needed here.
+ */
+ return fsd->real_fops;
+}
+EXPORT_SYMBOL_GPL(debugfs_real_fops);
+
static int open_proxy_open(struct inode *inode, struct file *filp)
{
const struct dentry *dentry = F_DENTRY(filp);
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 7fd4ec4bb214..1ae133064ca1 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -185,6 +185,11 @@ static const struct super_operations debugfs_super_operations = {
.evict_inode = debugfs_evict_inode,
};

+static void debugfs_release_dentry(struct dentry *dentry)
+{
+ kfree(dentry->d_fsdata);
+}
+
static struct vfsmount *debugfs_automount(struct path *path)
{
debugfs_automount_t f;
@@ -194,6 +199,7 @@ static struct vfsmount *debugfs_automount(struct path *path)

static const struct dentry_operations debugfs_dops = {
.d_delete = always_delete_dentry,
+ .d_release = debugfs_release_dentry,
.d_automount = debugfs_automount,
};

@@ -343,24 +349,34 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
{
struct dentry *dentry;
struct inode *inode;
+ struct debugfs_fsdata *fsd;
+
+ fsd = kmalloc(sizeof(*fsd), GFP_KERNEL);
+ if (!fsd)
+ return NULL;

if (!(mode & S_IFMT))
mode |= S_IFREG;
BUG_ON(!S_ISREG(mode));
dentry = start_creating(name, parent);

- if (IS_ERR(dentry))
+ if (IS_ERR(dentry)) {
+ kfree(fsd);
return NULL;
+ }

inode = debugfs_get_inode(dentry->d_sb);
- if (unlikely(!inode))
+ if (unlikely(!inode)) {
+ kfree(fsd);
return failed_creating(dentry);
+ }

inode->i_mode = mode;
inode->i_private = data;

inode->i_fop = proxy_fops;
- dentry->d_fsdata = (void *)real_fops;
+ fsd->real_fops = real_fops;
+ dentry->d_fsdata = fsd;

d_instantiate(dentry, inode);
fsnotify_create(d_inode(dentry->d_parent), dentry);
diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h
index b3e8443a1f47..512601eed3ce 100644
--- a/fs/debugfs/internal.h
+++ b/fs/debugfs/internal.h
@@ -19,4 +19,8 @@ extern const struct file_operations debugfs_noop_file_operations;
extern const struct file_operations debugfs_open_proxy_file_operations;
extern const struct file_operations debugfs_full_proxy_file_operations;

+struct debugfs_fsdata {
+ const struct file_operations *real_fops;
+};
+
#endif /* _DEBUGFS_INTERNAL_H_ */
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 9174b0d28582..d614be21412a 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -45,23 +45,6 @@ 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(const 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;
-}
-
#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt) \
static int __fops ## _open(struct inode *inode, struct file *file) \
{ \
@@ -112,6 +95,9 @@ int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)

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

+const struct file_operations *debugfs_real_fops(const struct file *filp)
+ __must_hold(&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,
--
2.12.2
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