fuse: implement ->tmpfile()

This is basically equivalent to the FUSE_CREATE operation which creates and
opens a regular file.

Add a new FUSE_TMPFILE operation, otherwise just reuse the protocol and the
code for FUSE_CREATE.

Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dir.c

@@ -529,7 +529,7 @@ static int get_security_context(struct dentry *entry, umode_t mode,
  */
 static int fuse_create_open(struct inode *dir, struct dentry *entry,
 			    struct file *file, unsigned int flags,
-			    umode_t mode)
+			    umode_t mode, u32 opcode)
 {
 	int err;
 	struct inode *inode;
@@ -573,7 +573,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 		inarg.open_flags |= FUSE_OPEN_KILL_SUIDGID;
 	}
 
-	args.opcode = FUSE_CREATE;
+	args.opcode = opcode;
 	args.nodeid = get_node_id(dir);
 	args.in_numargs = 2;
 	args.in_args[0].size = sizeof(inarg);
@@ -676,7 +676,7 @@ static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
 	if (fc->no_create)
 		goto mknod;
 
-	err = fuse_create_open(dir, entry, file, flags, mode);
+	err = fuse_create_open(dir, entry, file, flags, mode, FUSE_CREATE);
 	if (err == -ENOSYS) {
 		fc->no_create = 1;
 		goto mknod;
@@ -802,6 +802,23 @@ static int fuse_create(struct user_namespace *mnt_userns, struct inode *dir,
 	return fuse_mknod(&init_user_ns, dir, entry, mode, 0);
 }
 
+static int fuse_tmpfile(struct user_namespace *mnt_userns, struct inode *dir,
+			struct file *file, umode_t mode)
+{
+	struct fuse_conn *fc = get_fuse_conn(dir);
+	int err;
+
+	if (fc->no_tmpfile)
+		return -EOPNOTSUPP;
+
+	err = fuse_create_open(dir, file->f_path.dentry, file, file->f_flags, mode, FUSE_TMPFILE);
+	if (err == -ENOSYS) {
+		fc->no_tmpfile = 1;
+		err = -EOPNOTSUPP;
+	}
+	return err;
+}
+
 static int fuse_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
 		      struct dentry *entry, umode_t mode)
 {
@@ -1913,6 +1930,7 @@ static const struct inode_operations fuse_dir_inode_operations = {
 	.setattr	= fuse_setattr,
 	.create		= fuse_create,
 	.atomic_open	= fuse_atomic_open,
+	.tmpfile	= fuse_tmpfile,
 	.mknod		= fuse_mknod,
 	.permission	= fuse_permission,
 	.getattr	= fuse_getattr,

fs/fuse/fuse_i.h

@@ -784,6 +784,9 @@ struct fuse_conn {
 	/* Does the filesystem support per inode DAX? */
 	unsigned int inode_dax:1;
 
+	/* Is tmpfile not implemented by fs? */
+	unsigned int no_tmpfile:1;
+
 	/** The number of requests waiting for completion */
 	atomic_t num_waiting;
 

include/uapi/linux/fuse.h

@@ -194,6 +194,9 @@
  *  - add FUSE_SECURITY_CTX init flag
  *  - add security context to create, mkdir, symlink, and mknod requests
  *  - add FUSE_HAS_INODE_DAX, FUSE_ATTR_DAX
+ *
+ *  7.37
+ *  - add FUSE_TMPFILE
  */
 
 #ifndef _LINUX_FUSE_H
@@ -229,7 +232,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 36
+#define FUSE_KERNEL_MINOR_VERSION 37
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -537,6 +540,7 @@ enum fuse_opcode {
 	FUSE_SETUPMAPPING	= 48,
 	FUSE_REMOVEMAPPING	= 49,
 	FUSE_SYNCFS		= 50,
+	FUSE_TMPFILE		= 51,
 
 	/* CUSE specific operations */
 	CUSE_INIT		= 4096,