[PATCH 1/2] fs: Add fd_install file operation

[Kalesh Singh]

Provides a per process hook for the acquisition of file descriptors,
despite the method used to obtain the descriptor.

Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
---
 Documentation/filesystems/vfs.rst | 5 +++++
 fs/file.c                         | 3 +++
 include/linux/fs.h                | 1 +
 3 files changed, 9 insertions(+)

diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index ed17771c212b..95b30142c8d9 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -1123,6 +1123,11 @@ otherwise noted.
 ``fadvise``
 	possibly called by the fadvise64() system call.
 
+``fd_install``
+	called by the VFS when a file descriptor is installed in the
+	process's file descriptor table, regardless how the file descriptor
+	was acquired -- be it via the open syscall, received over IPC, etc.
+
 Note that the file operations are implemented by the specific
 filesystem in which the inode resides.  When opening a device node
 (character or block special) most filesystems will call special
diff --git a/fs/file.c b/fs/file.c
index abb8b7081d7a..f5db8622b851 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -616,6 +616,9 @@ void __fd_install(struct files_struct *files, unsigned int fd,
 void fd_install(unsigned int fd, struct file *file)
 {
 	__fd_install(current->files, fd, file);
+
+	if (file->f_op->fd_install)
+		file->f_op->fd_install(fd, file);
 }
 
 EXPORT_SYMBOL(fd_install);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f5abba86107d..b976fbe8c902 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1864,6 +1864,7 @@ struct file_operations {
 				   struct file *file_out, loff_t pos_out,
 				   loff_t len, unsigned int remap_flags);
 	int (*fadvise)(struct file *, loff_t, loff_t, int);
+	void (*fd_install)(int, struct file *);
 } __randomize_layout;
 
 struct inode_operations {
-- 
2.28.0.163.g6104cc2f0b6-goog