/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2006  Miklos Szeredi <miklos@szeredi.hu>

  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.
*/

#include <linux/fuse.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/wait.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/mm.h>
#include <linux/backing-dev.h>
#include <linux/mutex.h>

/** Max number of pages that can be used in a single read request */
#define FUSE_MAX_PAGES_PER_REQ 32

/** Maximum number of outstanding background requests */
#define FUSE_MAX_BACKGROUND 12

/** Congestion starts at 75% of maximum */
#define FUSE_CONGESTION_THRESHOLD (FUSE_MAX_BACKGROUND * 75 / 100)

/** It could be as large as PATH_MAX, but would that have any uses? */
#define FUSE_NAME_MAX 1024

/** Number of dentries for each connection in the control filesystem */
#define FUSE_CTL_NUM_DENTRIES 3

/** If the FUSE_DEFAULT_PERMISSIONS flag is given, the filesystem
    module will check permissions based on the file mode.  Otherwise no
    permission checking is done in the kernel */
#define FUSE_DEFAULT_PERMISSIONS (1 << 0)

/** If the FUSE_ALLOW_OTHER flag is given, then not only the user
    doing the mount will be allowed to access the filesystem */
#define FUSE_ALLOW_OTHER         (1 << 1)

/** List of active connections */
extern struct list_head fuse_conn_list;

/** Global mutex protecting fuse_conn_list and the control filesystem */
extern struct mutex fuse_mutex;

/** FUSE inode */
struct fuse_inode {
        /** Inode data */
        struct inode inode;

        /** Unique ID, which identifies the inode between userspace
         * and kernel */
        u64 nodeid;

        /** Number of lookups on this inode */
        u64 nlookup;

        /** The request used for sending the FORGET message */
        struct fuse_req *forget_req;

        /** Time in jiffies until the file attributes are valid */
        u64 i_time;

        /** The sticky bit in inode->i_mode may have been removed, so
            preserve the original mode */
        mode_t orig_i_mode;

        /** Version of last attribute change */
        u64 attr_version;

        /** Files usable in writepage.  Protected by fc->lock */
        struct list_head write_files;
};

/** FUSE specific file data */
struct fuse_file {
        /** Request reserved for flush and release */
        struct fuse_req *reserved_req;

        /** File handle used by userspace */
        u64 fh;

        /** Refcount */
        atomic_t count;

        /** Entry on inode's write_files list */
        struct list_head write_entry;
};

/** One input argument of a request */
struct fuse_in_arg {
        unsigned size;
        const void *value;
};

/** The request input */
struct fuse_in {
        /** The request header */
        struct fuse_in_header h;

        /** True if the data for the last argument is in req->pages */
        unsigned argpages:1;

        /** Number of arguments */
        unsigned numargs;

        /** Array of arguments */
        struct fuse_in_arg args[3];
};

/** One output argument of a request */
struct fuse_arg {
        unsigned size;
        void *value;
};

/** The request output */
struct fuse_out {
        /** Header returned from userspace */
        struct fuse_out_header h;

        /*
         * The following bitfields are not changed during the request
         * processing
         */

        /** Last argument is variable length (can be shorter than
            arg->size) */
        unsigned argvar:1;

        /** Last argument is a list of pages to copy data to */
        unsigned argpages:1;

        /** Zero partially or not copied pages */
        unsigned page_zeroing:1;

        /** Number or arguments */
        unsigned numargs;

        /** Array of arguments */
        struct fuse_arg args[3];
};

/** The request state */
enum fuse_req_state {
        FUSE_REQ_INIT = 0,
        FUSE_REQ_PENDING,
        FUSE_REQ_READING,
        FUSE_REQ_SENT,
        FUSE_REQ_WRITING,
        FUSE_REQ_FINISHED
};

struct fuse_conn;

/**
 * A request to the client
 */
struct fuse_req {
        /** This can be on either pending processing or io lists in
            fuse_conn */
        struct list_head list;

        /** Entry on the interrupts list  */
        struct list_head intr_entry;

        /** refcount */
        atomic_t count;

        /** Unique ID for the interrupt request */
        u64 intr_unique;

        /*
         * The following bitfields are either set once before the
         * request is queued or setting/clearing them is protected by
         * fuse_conn->lock
         */

        /** True if the request has reply */
        unsigned isreply:1;

        /** Force sending of the request even if interrupted */
        unsigned force:1;

        /** The request was aborted */
        unsigned aborted:1;

        /** Request is sent in the background */
        unsigned background:1;

        /** The request has been interrupted */
        unsigned interrupted:1;

        /** Data is being copied to/from the request */
        unsigned locked:1;

        /** Request is counted as "waiting" */
        unsigned waiting:1;

        /** State of the request */
        enum fuse_req_state state;

        /** The request input */
        struct fuse_in in;

        /** The request output */
        struct fuse_out out;

        /** Used to wake up the task waiting for completion of request*/
        wait_queue_head_t waitq;

        /** Data for asynchronous requests */
        union {
                struct fuse_forget_in forget_in;
                struct {
                        struct fuse_release_in in;
                        struct vfsmount *vfsmount;
                        struct dentry *dentry;
                } release;
                struct fuse_init_in init_in;
                struct fuse_init_out init_out;
                struct fuse_read_in read_in;
                struct {
                        struct fuse_write_in in;
                        struct fuse_write_out out;
                } write;
                struct fuse_lk_in lk_in;
        } misc;

        /** page vector */
        struct page *pages[FUSE_MAX_PAGES_PER_REQ];

        /** number of pages in vector */
        unsigned num_pages;

        /** offset of data on first page */
        unsigned page_offset;

        /** File used in the request (or NULL) */
        struct fuse_file *ff;

        /** Request completion callback */
        void (*end)(struct fuse_conn *, struct fuse_req *);

        /** Request is stolen from fuse_file->reserved_req */
        struct file *stolen_file;
};

/**
 * A Fuse connection.
 *
 * This structure is created, when the filesystem is mounted, and is
 * destroyed, when the client device is closed and the filesystem is
 * unmounted.
 */
struct fuse_conn {
        /** Lock protecting accessess to  members of this structure */
        spinlock_t lock;

        /** Mutex protecting against directory alias creation */
        struct mutex inst_mutex;

        /** Refcount */
        atomic_t count;

        /** The user id for this mount */
        uid_t user_id;

        /** The group id for this mount */
        gid_t group_id;

        /** The fuse mount flags for this mount */
        unsigned flags;

        /** Maximum read size */
        unsigned max_read;

        /** Maximum write size */
        unsigned max_write;

        /** Readers of the connection are waiting on this */
        wait_queue_head_t waitq;

        /** The list of pending requests */
        struct list_head pending;

        /** The list of requests being processed */
        struct list_head processing;

        /** The list of requests under I/O */
        struct list_head io;

        /** Number of requests currently in the background */
        unsigned num_background;

        /** Number of background requests currently queued for userspace */
        unsigned active_background;

        /** The list of background requests set aside for later queuing */
        struct list_head bg_queue;

        /** Pending interrupts */
        struct list_head interrupts;

        /** Flag indicating if connection is blocked.  This will be
            the case before the INIT reply is received, and if there
            are too many outstading backgrounds requests */
        int blocked;

        /** waitq for blocked connection */
        wait_queue_head_t blocked_waitq;

        /** waitq for reserved requests */
        wait_queue_head_t reserved_req_waitq;

        /** The next unique request id */
        u64 reqctr;

        /** Connection established, cleared on umount, connection
            abort and device release */
        unsigned connected;

        /** Connection failed (version mismatch).  Cannot race with
            setting other bitfields since it is only set once in INIT
            reply, before any other request, and never cleared */
        unsigned conn_error : 1;

        /** Connection successful.  Only set in INIT */
        unsigned conn_init : 1;

        /** Do readpages asynchronously?  Only set in INIT */
        unsigned async_read : 1;

        /** Do not send separate SETATTR request before open(O_TRUNC)  */
        unsigned atomic_o_trunc : 1;

        /*
         * The following bitfields are only for optimization purposes
         * and hence races in setting them will not cause malfunction
         */

        /** Is fsync not implemented by fs? */
        unsigned no_fsync : 1;

        /** Is fsyncdir not implemented by fs? */
        unsigned no_fsyncdir : 1;

        /** Is flush not implemented by fs? */
        unsigned no_flush : 1;

        /** Is setxattr not implemented by fs? */
        unsigned no_setxattr : 1;

        /** Is getxattr not implemented by fs? */
        unsigned no_getxattr : 1;

        /** Is listxattr not implemented by fs? */
        unsigned no_listxattr : 1;

        /** Is removexattr not implemented by fs? */
        unsigned no_removexattr : 1;

        /** Are file locking primitives not implemented by fs? */
        unsigned no_lock : 1;

        /** Is access not implemented by fs? */
        unsigned no_access : 1;

        /** Is create not implemented by fs? */
        unsigned no_create : 1;

        /** Is interrupt not implemented by fs? */
        unsigned no_interrupt : 1;

        /** Is bmap not implemented by fs? */
        unsigned no_bmap : 1;

        /** The number of requests waiting for completion */
        atomic_t num_waiting;

        /** Negotiated minor version */
        unsigned minor;

        /** Backing dev info */
        struct backing_dev_info bdi;

        /** Entry on the fuse_conn_list */
        struct list_head entry;

        /** Unique ID */
        u64 id;

        /** Dentries in the control filesystem */
        struct dentry *ctl_dentry[FUSE_CTL_NUM_DENTRIES];

        /** number of dentries used in the above array */
        int ctl_ndents;

        /** O_ASYNC requests */
        struct fasync_struct *fasync;

        /** Key for lock owner ID scrambling */
        u32 scramble_key[4];

        /** Reserved request for the DESTROY message */
        struct fuse_req *destroy_req;

        /** Version counter for attribute changes */
        u64 attr_version;
};

static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
{
        return sb->s_fs_info;
}

static inline struct fuse_conn *get_fuse_conn(struct inode *inode)
{
        return get_fuse_conn_super(inode->i_sb);
}

static inline struct fuse_inode *get_fuse_inode(struct inode *inode)
{
        return container_of(inode, struct fuse_inode, inode);
}

static inline u64 get_node_id(struct inode *inode)
{
        return get_fuse_inode(inode)->nodeid;
}

/** Device operations */
extern const struct file_operations fuse_dev_operations;

/**
 * Get a filled in inode
 */
struct inode *fuse_iget(struct super_block *sb, unsigned long nodeid,
                        int generation, struct fuse_attr *attr,
                        u64 attr_valid, u64 attr_version);

/**
 * Send FORGET command
 */
void fuse_send_forget(struct fuse_conn *fc, struct fuse_req *req,
                      unsigned long nodeid, u64 nlookup);

/**
 * Initialize READ or READDIR request
 */
void fuse_read_fill(struct fuse_req *req, struct file *file,
                    struct inode *inode, loff_t pos, size_t count, int opcode);

/**
 * Send OPEN or OPENDIR request
 */
int fuse_open_common(struct inode *inode, struct file *file, int isdir);

struct fuse_file *fuse_file_alloc(void);
void fuse_file_free(struct fuse_file *ff);
void fuse_finish_open(struct inode *inode, struct file *file,
                      struct fuse_file *ff, struct fuse_open_out *outarg);

/** Fill in ff->reserved_req with a RELEASE request */
void fuse_release_fill(struct fuse_file *ff, u64 nodeid, int flags, int opcode);

/**
 * Send RELEASE or RELEASEDIR request
 */
int fuse_release_common(struct inode *inode, struct file *file, int isdir);

/**
 * Send FSYNC or FSYNCDIR request
 */
int fuse_fsync_common(struct file *file, struct dentry *de, int datasync,
                      int isdir);

/**
 * Initialize file operations on a regular file
 */
void fuse_init_file_inode(struct inode *inode);

/**
 * Initialize inode operations on regular files and special files
 */
void fuse_init_common(struct inode *inode);

/**
 * Initialize inode and file operations on a directory
 */
void fuse_init_dir(struct inode *inode);

/**
 * Initialize inode operations on a symlink
 */
void fuse_init_symlink(struct inode *inode);

/**
 * Change attributes of an inode
 */
void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
                            u64 attr_valid, u64 attr_version);

/**
 * Initialize the client device
 */
int fuse_dev_init(void);

/**
 * Cleanup the client device
 */
void fuse_dev_cleanup(void);

int fuse_ctl_init(void);
void fuse_ctl_cleanup(void);

/**
 * Allocate a request
 */
struct fuse_req *fuse_request_alloc(void);

/**
 * Free a request
 */
void fuse_request_free(struct fuse_req *req);

/**
 * Get a request, may fail with -ENOMEM
 */
struct fuse_req *fuse_get_req(struct fuse_conn *fc);

/**
 * Gets a requests for a file operation, always succeeds
 */
struct fuse_req *fuse_get_req_nofail(struct fuse_conn *fc, struct file *file);

/**
 * Decrement reference count of a request.  If count goes to zero free
 * the request.
 */
void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req);

/**
 * Send a request (synchronous)
 */
void request_send(struct fuse_conn *fc, struct fuse_req *req);

/**
 * Send a request with no reply
 */
void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req);

/**
 * Send a request in the background
 */
void request_send_background(struct fuse_conn *fc, struct fuse_req *req);

/* Abort all requests */
void fuse_abort_conn(struct fuse_conn *fc);

/**
 * Invalidate inode attributes
 */
void fuse_invalidate_attr(struct inode *inode);

/**
 * Acquire reference to fuse_conn
 */
struct fuse_conn *fuse_conn_get(struct fuse_conn *fc);

/**
 * Release reference to fuse_conn
 */
void fuse_conn_put(struct fuse_conn *fc);

/**
 * Add connection to control filesystem
 */
int fuse_ctl_add_conn(struct fuse_conn *fc);

/**
 * Remove connection from control filesystem
 */
void fuse_ctl_remove_conn(struct fuse_conn *fc);

/**
 * Is file type valid?
 */
int fuse_valid_type(int m);

/**
 * Is task allowed to perform filesystem operation?
 */
int fuse_allow_task(struct fuse_conn *fc, struct task_struct *task);

u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id);

int fuse_update_attributes(struct inode *inode, struct kstat *stat,
                           struct file *file, bool *refreshed);