CUSE: implement CUSE - Character device in Userspace
CUSE enables implementing character devices in userspace. With recent
additions of ioctl and poll support, FUSE already has most of what's
necessary to implement character devices. All CUSE has to do is
bonding all those components - FUSE, chardev and the driver model -
nicely.
When client opens /dev/cuse, kernel starts conversation with
CUSE_INIT. The client tells CUSE which device it wants to create. As
the previous patch made fuse_file usable without associated
fuse_inode, CUSE doesn't create super block or inodes. It attaches
fuse_file to cdev file->private_data during open and set ff->fi to
NULL. The rest of the operation is almost identical to FUSE direct IO
case.
Each CUSE device has a corresponding directory /sys/class/cuse/DEVNAME
(which is symlink to /sys/devices/virtual/class/DEVNAME if
SYSFS_DEPRECATED is turned off) which hosts "waiting" and "abort"
among other things. Those two files have the same meaning as the FUSE
control files.
The only notable lacking feature compared to in-kernel implementation
is mmap support.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/include/linux/fuse.h b/include/linux/fuse.h
index 162e5de..d41ed59 100644
--- a/include/linux/fuse.h
+++ b/include/linux/fuse.h
@@ -121,6 +121,13 @@
#define FUSE_BIG_WRITES (1 << 5)
/**
+ * CUSE INIT request/reply flags
+ *
+ * CUSE_UNRESTRICTED_IOCTL: use unrestricted ioctl
+ */
+#define CUSE_UNRESTRICTED_IOCTL (1 << 0)
+
+/**
* Release flags
*/
#define FUSE_RELEASE_FLUSH (1 << 0)
@@ -210,6 +217,9 @@
FUSE_DESTROY = 38,
FUSE_IOCTL = 39,
FUSE_POLL = 40,
+
+ /* CUSE specific operations */
+ CUSE_INIT = 4096,
};
enum fuse_notify_code {
@@ -401,6 +411,27 @@
__u32 max_write;
};
+#define CUSE_INIT_INFO_MAX 4096
+
+struct cuse_init_in {
+ __u32 major;
+ __u32 minor;
+ __u32 unused;
+ __u32 flags;
+};
+
+struct cuse_init_out {
+ __u32 major;
+ __u32 minor;
+ __u32 unused;
+ __u32 flags;
+ __u32 max_read;
+ __u32 max_write;
+ __u32 dev_major; /* chardev major */
+ __u32 dev_minor; /* chardev minor */
+ __u32 spare[10];
+};
+
struct fuse_interrupt_in {
__u64 unique;
};