debugfs: get rid of dynamically allocation proxy_ops

All it takes is having full_proxy_open() collect the information
about available methods and store it in debugfs_fsdata.

Wrappers are called only after full_proxy_open() has succeeded
calling debugfs_get_file(), so they are guaranteed to have
->d_fsdata already pointing to debugfs_fsdata.

As the result, they can check if method is absent and bugger off
early, without any atomic operations, etc. - same effect as what
we'd have from NULL method.  Which makes the entire proxy_fops
contents unconditional, making it completely pointless - we can
just put those methods (unconditionally) into
debugfs_full_proxy_file_operations and forget about dynamic
allocation, replace_fops, etc.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20250112080705.141166-3-viro@zeniv.linux.org.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h
index a644e44a0ee4..011ef8b1a99a 100644
--- a/fs/debugfs/internal.h
+++ b/fs/debugfs/internal.h
@@ -39,9 +39,18 @@ struct debugfs_fsdata {
 		/* protect cancellations */
 		struct mutex cancellations_mtx;
 		struct list_head cancellations;
+		unsigned int methods;
 	};
 };
 
+enum {
+	HAS_READ = 1,
+	HAS_WRITE = 2,
+	HAS_LSEEK = 4,
+	HAS_POLL = 8,
+	HAS_IOCTL = 16
+};
+
 /*
  * A dentry's ->d_fsdata either points to the real fops or to a
  * dynamically allocated debugfs_fsdata instance.