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[Written by Terje Oseberg]
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When your user mode program calls fuse_main() (lib/helper.c),
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fuse_main() parses the arguments passed to your user mode program,
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then calls fuse_mount() (lib/mount.c).
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fuse_mount() creates a UNIX domain socket, then forks and execs
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fusermount (util/fusermount.c) passing it one end of the socket in the
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FUSE_COMMFD_ENV environment variable.
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fusermount (util/fusermount.c) makes sure that the fuse module is
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loaded. fusermount then open /proc/fs/fuse/dev and send the file
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handle over a UNIX domain socket back to fuse_mount().
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fuse_mount() returns the filehandle for /proc/fs/fuse/dev to fuse_main().
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fuse_main() calls fuse_new() (lib/fuse.c) which allocates the struct
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fuse datastructure that stores and maintains a cached image of the
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Lastly, fuse_main() calls either fuse_loop() (lib/fuse.c) or
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fuse_loop_mt() (lib/fuse_mt.c) which both start to read the filesystem
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system calls from the /proc/fs/fuse/dev, call the usermode functions
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stored in struct fuse_operations datastructure before calling
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fuse_main(). The results of those calls are then written back to the
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/proc/fs/fuse/dev file where they can be forwarded back to the system
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The kernel module consists of two parts. First the proc filesystem
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component in kernel/dev.c -and second the filesystem system calls
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kernel/file.c, kernel/inode.c, and kernel/dir.c
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All the system calls in kernel/file.c, kernel/inode.c, and
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kernel/dir.c make calls to either request_send(),
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request_send_noreply(), or request_send_nonblock(). Most of the calls
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(all but 2) are to request_send(). request_send() adds the request to,
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"list of requests" structure (fc->pending), then waits for a response.
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request_send_noreply() and request_send_nonblock() are both similar in
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function to request_send() except that one is non-blocking, and the
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other does not respond with a reply.
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The proc filesystem component in kernel/dev.c responds to file io
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requests to the file /proc/fs/fuse/dev. fuse_dev_read() handles the
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file reads and returns commands from the "list of requests" structure
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to the calling program. fuse_dev_write() handles file writes and takes
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the data written and places them into the req->out datastructure where
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they can be returned to the system call through the "list of requests"
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structure and request_send().
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doc/how-fuse-works
