[PATCH v3 6/7] debugfs: unproxify files created through debugfs_create_blob()

[Nicolai Stange]

Currently, the struct file_operations fops_blob associated with files
created through the debugfs_create_blob() helpers are not file
lifetime aware.

Thus, a lifetime managing proxy is created around fops_blob each time such
a file is opened which is an unnecessary waste of resources.

Implement file lifetime management for the fops_bool file_operations.
Namely, make read_file_blob() safe gainst file removals by means of
debugfs_use_file_start() and debugfs_use_file_finish().

Make debugfs_create_blob() create its files in non-proxying operation mode
by means of debugfs_create_file_unsafe().

Signed-off-by: Nicolai Stange <nicsta...@gmail.com>
---
 fs/debugfs/file.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index da24e0b..036ec3f 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -843,8 +843,15 @@ static ssize_t read_file_blob(struct file *file, char 
__user *user_buf,
                              size_t count, loff_t *ppos)
 {
        struct debugfs_blob_wrapper *blob = file->private_data;
-       return simple_read_from_buffer(user_buf, count, ppos, blob->data,
-                       blob->size);
+       ssize_t r;
+       int srcu_idx;
+
+       r = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
+       if (likely(!r))
+               r = simple_read_from_buffer(user_buf, count, ppos, blob->data,
+                                       blob->size);
+       debugfs_use_file_finish(srcu_idx);
+       return r;
 }
 
 static const struct file_operations fops_blob = {
@@ -881,7 +888,7 @@ struct dentry *debugfs_create_blob(const char *name, 
umode_t mode,
                                   struct dentry *parent,
                                   struct debugfs_blob_wrapper *blob)
 {
-       return debugfs_create_file(name, mode, parent, blob, &fops_blob);
+       return debugfs_create_file_unsafe(name, mode, parent, blob, &fops_blob);
 }
 EXPORT_SYMBOL_GPL(debugfs_create_blob);
 
-- 
2.7.1