How Fuse-1.3 Works[Written by Terje Oseberg]1. The fuse library.When your user mode program calls fuse_main() (lib/helper.c),fuse_main() parses the arguments passed to your user mode program,then calls fuse_mount() (lib/mount.c).fuse_mount() creates a UNIX domain socket pair, then forks and execsfusermount (util/fusermount.c) passing it one end of the socket in theFUSE_COMMFD_ENV environment variable.fusermount (util/fusermount.c) makes sure that the fuse module isloaded. fusermount then open /dev/fuse and send the file handle over aUNIX domain socket back to fuse_mount().fuse_mount() returns the filehandle for /dev/fuse to fuse_main().fuse_main() calls fuse_new() (lib/fuse.c) which allocates the structfuse datastructure that stores and maintains a cached image of thefilesystem data.Lastly, fuse_main() calls either fuse_loop() (lib/fuse.c) orfuse_loop_mt() (lib/fuse_mt.c) which both start to read the filesystemsystem calls from the /dev/fuse, call the usermode functionsstored in struct fuse_operations datastructure before callingfuse_main(). The results of those calls are then written back to the/dev/fuse file where they can be forwarded back to the systemcalls.2. The kernel module.The kernel module consists of two parts. First the proc filesystemcomponent in kernel/dev.c -and second the filesystem system callskernel/file.c, kernel/inode.c, and kernel/dir.cAll the system calls in kernel/file.c, kernel/inode.c, andkernel/dir.c make calls to either request_send(),request_send_noreply(), or request_send_nonblock(). Most of the calls(all but 2) are to request_send(). request_send() adds the request to,"list of requests" structure (fc->pending), then waits for a response.request_send_noreply() and request_send_nonblock() are both similar infunction to request_send() except that one is non-blocking, and theother does not respond with a reply.The proc filesystem component in kernel/dev.c responds to file iorequests to the file /dev/fuse. fuse_dev_read() handles thefile reads and returns commands from the "list of requests" structureto the calling program. fuse_dev_write() handles file writes and takesthe data written and places them into the req->out datastructure wherethey can be returned to the system call through the "list of requests"structure and request_send().