[RFC PATCH v4 21/36] fuse-bpf: Add partial flock support

[Daniel Rosenberg <drosen@google.com>]

This adds passthrough support for flock on fuse-bpf files. It does not
give any control via a bpf filter. The flock will act as though it was
taken on the lower file.

see fuse_test -t32 (flock_test)

Signed-off-by: Daniel Rosenberg <drosen@google.com>
---
 fs/fuse/backing.c | 15 +++++++++++++++
 fs/fuse/file.c    |  9 +++++++--
 fs/fuse/fuse_i.h  |  1 +
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index f18aee297335..b2df2469c29c 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -9,6 +9,7 @@
 #include <linux/bpf_fuse.h>
 #include <linux/fdtable.h>
 #include <linux/file.h>
+#include <linux/filelock.h>
 #include <linux/fs_stack.h>
 #include <linux/namei.h>
 #include <linux/splice.h>
@@ -1586,6 +1587,20 @@ int fuse_bpf_file_write_iter(ssize_t *out, struct inode *inode, struct kiocb *io
 				iocb, from);
 }
 
+int fuse_file_flock_backing(struct file *file, int cmd, struct file_lock *fl)
+{
+	struct fuse_file *ff = file->private_data;
+	struct file *backing_file = ff->backing_file;
+	int error;
+
+	fl->fl_file = backing_file;
+	if (backing_file->f_op->flock)
+		error = backing_file->f_op->flock(backing_file, cmd, fl);
+	else
+		error = locks_lock_file_wait(backing_file, fl);
+	return error;
+}
+
 ssize_t fuse_backing_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	int ret;
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 46de67810f03..255eb59d04f8 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2676,13 +2676,18 @@ static int fuse_file_flock(struct file *file, int cmd, struct file_lock *fl)
 {
 	struct inode *inode = file_inode(file);
 	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_file *ff = file->private_data;
 	int err;
 
+#ifdef CONFIG_FUSE_BPF
+	/* TODO - this is simply passthrough, not a proper BPF filter */
+	if (ff->backing_file)
+		return fuse_file_flock_backing(file, cmd, fl);
+#endif
+
 	if (fc->no_flock) {
 		err = locks_lock_file_wait(file, fl);
 	} else {
-		struct fuse_file *ff = file->private_data;
-
 		/* emulate flock with POSIX locks */
 		ff->flock = true;
 		err = fuse_setlk(file, fl, 1);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 8ae6ad967f95..e69f83616909 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1651,6 +1651,7 @@ static inline int fuse_bpf_access(int *out, struct inode *inode, int mask)
 
 #endif // CONFIG_FUSE_BPF
 
+int fuse_file_flock_backing(struct file *file, int cmd, struct file_lock *fl);
 ssize_t fuse_backing_mmap(struct file *file, struct vm_area_struct *vma);
 
 int fuse_handle_backing(struct fuse_bpf_entry *fbe, struct path *backing_path);
-- 
2.44.0.478.gd926399ef9-goog