CUSE(3)

NAME
libcuse - Userland character device library

LIBRARY
libcuse

SYNOPSIS
To load the required kernel module at boot time, place the following line in loader.conf(5):

    cuse_load="YES"

#include <cuse.h>

DESCRIPTION
The libcuse library contains functions to create a character device in userspace. The libcuse library is thread safe.

LIBRARY INITIALISATION / DEINITIALISATION
int cuse_init(void) This function initialises libcuse. Must be called at the beginning of the program. This function returns 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes. If the cuse kernel module is not loaded, CUSE_ERR_NOT_LOADED is returned.

int cuse_uninit(void) Deinitialise libcuse. Can be called at the end of the application. This function returns 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes.

UNIT MANAGEMENT
int cuse_alloc_unit_number(int *) This function stores a uniq system unit number at the pointed integer loation. This function returns 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes.

int cuse_alloc_unit_number_by_id(int *, int id) This function stores a unique system unit number at the pointed integer loation. The returned unit number is uniq within the given ID. Valid ID values are defined by the cuse include file. See the CUSE_ID_XXX() macros for more information. This function returns 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes.

int cuse_free_unit_number(int) This function frees the given allocated system unit number. This function returns 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes.

int cuse_free_unit_number_by_id(int unit, int id) This function frees the given allocated system unit number belonging to the given ID. If both the unit and id argument is -1, all allocated units will be freed. This function returns 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes.

LIBRARY USAGE
void * cuse_vmalloc(unsigned size) This function allocates size bytes of memory. Only memory allocated by this function can be memory mapped by mmap(2). This function returns a valid data pointer on success or NULL on failure. The returned pointer is always aligned to the system page size. The number and size of allocations is limited by the mmap(2) offset having to fit into a 32-bit variable typically for 32-bit applications.

int cuse_is_vmalloc_addr(void *) This function returns non-zero if the passed pointer points to a valid and non-freed allocation, as returned by cuse_vmalloc(). Else this function returns zero.

void cuse_vmfree(void *) This function frees memory allocated by cuse_vmalloc(). This function is NULL safe.

unsigned long cuse_vmoffset(void *) This function returns the mmap offset the client must use to access the allocated memory. The passed pointer must be aligned to the system page size.

struct cuse_dev * cuse_dev_create(const struct cuse_methods *mtod, void *priv0, void *priv1, uid_t, gid_t, int permission, const char *fmt, ...) This function creates a new character device according to the given parameters. This function returns a valid cuse_dev structure pointer on success or NULL on failure. The device name can only contain a-z, A-Z, 0-9, dot, / and underscore characters.

void cuse_dev_destroy(struct cuse_dev *) This functions destroys a previously created character device.

void * cuse_dev_get_priv0(struct cuse_dev *), void * cuse_dev_get_priv1(struct cuse_dev *), void cuse_dev_set_priv0(struct cuse_dev *, void *), void cuse_dev_set_priv1(struct cuse_dev *, void *) These functions are used to set and get the private data of the given cuse device.

int cuse_wait_and_process(void) This function will block and do event processing. If parallel I/O is required multiple threads must be created looping on this function. This function returns 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes.

void * cuse_dev_get_per_file_handle(struct cuse_dev *), void cuse_dev_set_per_file_handle(struct cuse_dev *, void *) These functions are used to set and get the per-file-open specific handle and should only be used inside the cuse file operation callbacks.

void cuse_set_local(int) This function instructs cuse_copy_out() and cuse_copy_in() that the user pointer is local, if the argument passed to it is non-zero. Else the user pointer is assumed to be at the peer application. This function should only be used inside the cuse file operation callbacks. The value is reset to zero when the given file operation returns, and does not affect any other file operation callbacks.

int cuse_get_local(void) Returns the current local state. See cuse_set_local().

int cuse_copy_out(const void *src, void *peer_dst, int len), int cuse_copy_in(const void *peer_src, void *dst, int len) These functions are used to transfer data between the local application and the peer application. These functions must be used when operating on the data pointers passed to the cm_read(), cm_write(), and cm_ioctl() callback functions. These functions return 0 on success or a negative value on failure. See CUSE_ERR_XXX for known error codes.

int cuse_got_peer_signal(void) This function is used to check if a signal has been delivered to the peer application and should only be used inside the cuse file operation callbacks. This function returns 0 if a signal has been delivered to the caller. Else it returns a negative value. See CUSE_ERR_XXX for known error codes.

struct cuse_dev * cuse_dev_get_current(int *pcmd) This function is used to get the current cuse device pointer and the currently executing command, by CUSE_CMD_XXX value. The pcmd argument is allowed to be NULL. This function should only be used inside the cuse file operation callbacks. On success a valid cuse device pointer is returned. On failure NULL is returned.

void cuse_poll_wakeup(void) This function will wake up any file pollers.

LIBRARY LIMITATIONS
Transfer lengths for read(), write(), cuse_copy_in(), and cuse_copy_out() should not exceed what can fit into a 32-bit signed integer and is defined by the CUSE_LENGTH_MAX() macro. Transfer lengths for ioctls should not exceed what is defined by the CUSE_BUFFER_MAX() macro.

LIBRARY CALLBACK METHODS
In general fflags are defined by CUSE_FFLAG_XXX and errors are defined by CUSE_ERR_XXX.

    enum {
      CUSE_ERR_NONE
      CUSE_ERR_BUSY
      CUSE_ERR_WOULDBLOCK
      CUSE_ERR_INVALID
      CUSE_ERR_NO_MEMORY
      CUSE_ERR_FAULT
      CUSE_ERR_SIGNAL
      CUSE_ERR_OTHER
      CUSE_ERR_NOT_LOADED
      CUSE_ERR_NO_DEVICE
      CUSE_POLL_NONE
      CUSE_POLL_READ
      CUSE_POLL_WRITE
      CUSE_POLL_ERROR
      CUSE_FFLAG_NONE
      CUSE_FFLAG_READ
      CUSE_FFLAG_WRITE
      CUSE_FFLAG_NONBLOCK
      CUSE_FFLAG_COMPAT32
      CUSE_CMD_NONE
      CUSE_CMD_OPEN
      CUSE_CMD_CLOSE
      CUSE_CMD_READ
      CUSE_CMD_WRITE
      CUSE_CMD_IOCTL
      CUSE_CMD_POLL
      CUSE_CMD_SIGNAL
      CUSE_CMD_SYNC
      CUSE_CMD_MAX
    };

int cuse_open_t(struct cuse_dev *, int fflags) This function returns a CUSE_ERR_XXX value.

int cuse_close_t(struct cuse_dev *, int fflags) This function returns a CUSE_ERR_XXX value.

int cuse_read_t(struct cuse_dev *, int fflags, void *peer_ptr, int len) This function returns a CUSE_ERR_XXX value in case of failure or the actually transferred length in case of success. cuse_copy_in() and cuse_copy_out() must be used to transfer data to and from the peer_ptr.

int cuse_write_t(struct cuse_dev *, int fflags, const void *peer_ptr, int len) This function returns a CUSE_ERR_XXX value in case of failure or the actually transferred length in case of success. cuse_copy_in() and cuse_copy_out() must be used to transfer data to and from the peer_ptr.

int cuse_ioctl_t(struct cuse_dev *, int fflags, unsigned long cmd, void *peer_data) This function returns a CUSE_ERR_XXX value in case of failure or zero in case of success. cuse_copy_in() and cuse_copy_out() must be used to transfer data to and from the peer_data.

int cuse_poll_t(struct cuse_dev *, int fflags, int events) This function returns a mask of CUSE_POLL_XXX values in case of failure and success. The events argument is also a mask of CUSE_POLL_XXX values.

    struct cuse_methods {
      cuse_open_t *cm_open;
      cuse_close_t *cm_close;
      cuse_read_t *cm_read;
      cuse_write_t *cm_write;
      cuse_ioctl_t *cm_ioctl;
      cuse_poll_t *cm_poll;
    };

HISTORY
libcuse was written by Hans Petter Selasky.