To simplify crash recovery and reduce performance impact, backing_ids
are not persisted across daemon restarts. After crash recovery, this
may lead to resource leaks if backing file resources are not properly
cleaned up.

Add FUSE_DEV_IOC_BACKING_CLOSE_ALL ioctl to release all backing_ids
and put backing files. When the FUSE daemon restarts, it can use this
ioctl to cleanup all backing file resources.

Signed-off-by: Chunsheng Luo <luochunsheng@ustc.edu>
---
 fs/fuse/backing.c         | 19 +++++++++++++++++++
 fs/fuse/dev.c             | 16 ++++++++++++++++
 fs/fuse/fuse_i.h          |  1 +
 include/uapi/linux/fuse.h |  1 +
 4 files changed, 37 insertions(+)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index 4afda419dd14..e93d797a2cde 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -166,6 +166,25 @@ int fuse_backing_close(struct fuse_conn *fc, int backing_id)
 	return err;
 }
 
+static int fuse_backing_close_one(int id, void *p, void *data)
+{
+	struct fuse_conn *fc = data;
+
+	fuse_backing_close(fc, id);
+
+	return 0;
+}
+
+int fuse_backing_close_all(struct fuse_conn *fc)
+{
+	if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	idr_for_each(&fc->backing_files_map, fuse_backing_close_one, fc);
+
+	return 0;
+}
+
 struct fuse_backing *fuse_backing_lookup(struct fuse_conn *fc, int backing_id)
 {
 	struct fuse_backing *fb;
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 6d59cbc877c6..f05d55302598 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2654,6 +2654,19 @@ static long fuse_dev_ioctl_backing_close(struct file *file, __u32 __user *argp)
 	return fuse_backing_close(fud->fc, backing_id);
 }
 
+static long fuse_dev_ioctl_backing_close_all(struct file *file)
+{
+	struct fuse_dev *fud = fuse_get_dev(file);
+
+	if (IS_ERR(fud))
+		return PTR_ERR(fud);
+
+	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+		return -EOPNOTSUPP;
+
+	return fuse_backing_close_all(fud->fc);
+}
+
 static long fuse_dev_ioctl_sync_init(struct file *file)
 {
 	int err = -EINVAL;
@@ -2682,6 +2695,9 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 	case FUSE_DEV_IOC_BACKING_CLOSE:
 		return fuse_dev_ioctl_backing_close(file, argp);
 
+	case FUSE_DEV_IOC_BACKING_CLOSE_ALL:
+		return fuse_dev_ioctl_backing_close_all(file);
+
 	case FUSE_DEV_IOC_SYNC_INIT:
 		return fuse_dev_ioctl_sync_init(file);
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 7f16049387d1..33e91a5d3765 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1573,6 +1573,7 @@ void fuse_backing_files_init(struct fuse_conn *fc);
 void fuse_backing_files_free(struct fuse_conn *fc);
 int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map);
 int fuse_backing_close(struct fuse_conn *fc, int backing_id);
+int fuse_backing_close_all(struct fuse_conn *fc);
 
 /* passthrough.c */
 static inline struct fuse_backing *fuse_inode_backing(struct fuse_inode *fi)
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index c13e1f9a2f12..e4ff28a4ff40 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -1139,6 +1139,7 @@ struct fuse_backing_map {
 					     struct fuse_backing_map)
 #define FUSE_DEV_IOC_BACKING_CLOSE	_IOW(FUSE_DEV_IOC_MAGIC, 2, uint32_t)
 #define FUSE_DEV_IOC_SYNC_INIT		_IO(FUSE_DEV_IOC_MAGIC, 3)
+#define FUSE_DEV_IOC_BACKING_CLOSE_ALL	_IO(FUSE_DEV_IOC_MAGIC, 4)
 
 struct fuse_lseek_in {
 	uint64_t	fh;
-- 
2.43.0