xref: /freebsd/lib/libcuse/cuse.3 (revision b2c76c41be32f904179efed29c0ca04d53f3996c)

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.Dd July 18, 2022
.Dt CUSE 3
.Os
.Sh NAME
.Nm libcuse
.Nd "Userland character device library"
.Sh LIBRARY
.Lb libcuse
.Sh SYNOPSIS
To load the required kernel module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
cuse_load="YES"
.Ed
.Pp
.In cuse.h
.Sh DESCRIPTION
The
.Nm
library contains functions to create a character device in userspace.
The
.Nm
library is thread safe.
.Sh LIBRARY INITIALISATION / DEINITIALISATION
.Ft "int"
.Fn "cuse_init" "void"
This function initialises
.Nm .
Must be called at the beginning of the program.
This function returns 0 on success or a negative value on failure.
See
.Dv CUSE_ERR_XXX
for known error codes.
If the cuse kernel module is not loaded,
.Dv CUSE_ERR_NOT_LOADED
is returned.
.Pp
.Ft "int"
.Fn "cuse_uninit" "void"
Deinitialise
.Nm .
Can be called at the end of the application.
This function returns 0 on success or a negative value on failure.
See
.Dv CUSE_ERR_XXX
for known error codes.
.Sh UNIT MANAGEMENT
.Ft "int"
.Fn "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
.Dv CUSE_ERR_XXX
for known error codes.
.Pp
.Ft "int"
.Fn "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
.Fn CUSE_ID_XXX
macros for more information.
This function returns 0 on success or a negative value on failure.
See
.Dv CUSE_ERR_XXX
for known error codes.
.Pp
.Ft "int"
.Fn "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
.Dv CUSE_ERR_XXX
for known error codes.
.Pp
.Ft "int"
.Fn "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
.Dv CUSE_ERR_XXX
for known error codes.
.Sh LIBRARY USAGE
.Ft "void *"
.Fn "cuse_vmalloc" "unsigned size"
This function allocates
.Ar size
bytes of memory.
Only memory allocated by this function can be memory
mapped by
.Xr mmap 2 .
This function returns a valid data pointer on success or
.Dv NULL
on failure.
The returned pointer is always aligned to the system page size.
The number and size of allocations is limited by the
.Xr mmap 2
offset having to fit into a 32-bit variable typically for 32-bit
applications.
.Pp
.Ft "int"
.Fn "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
.Fn cuse_vmalloc .
Else this function returns zero.
.Pp
.Ft "void"
.Fn "cuse_vmfree" "void *"
This function frees memory allocated by
.Fn cuse_vmalloc .
This function is NULL safe.
.Pp
.Ft "unsigned long"
.Fn "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.
.Pp
.Ft "struct cuse_dev *"
.Fn "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
.Dv NULL
on failure.
The device name can only contain a-z,
A-Z, 0-9, dot, / and underscore characters.
.Pp
.Ft "void"
.Fn "cuse_dev_destroy" "struct cuse_dev *"
This functions destroys a previously created character device.
.Pp
.Ft "void *"
.Fn "cuse_dev_get_priv0" "struct cuse_dev *" ,
.Ft "void *"
.Fn "cuse_dev_get_priv1" "struct cuse_dev *" ,
.Ft "void"
.Fn "cuse_dev_set_priv0" "struct cuse_dev *" "void *" ,
.Ft "void"
.Fn "cuse_dev_set_priv1" "struct cuse_dev *" "void *"
These functions are used to set and get the private data of the given
cuse device.
.Pp
.Ft "int"
.Fn "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
.Dv CUSE_ERR_XXX
for known error codes.
.Pp
.Ft "void *"
.Fn "cuse_dev_get_per_file_handle" "struct cuse_dev *" ,
.Ft "void"
.Fn "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.
.Pp
.Ft "void"
.Fn "cuse_set_local" "int"
This function instructs
.Fn cuse_copy_out
and
.Fn 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.
.Pp
.Ft "int"
.Fn "cuse_get_local" "void"
Returns the current local state.
See
.Fn cuse_set_local .
.Pp
.Ft "int"
.Fn "cuse_copy_out" "const void *src" "void *peer_dst" "int len" ,
.Ft "int"
.Fn "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
.Fn cm_read ,
.Fn cm_write ,
and
.Fn cm_ioctl
callback functions.
These functions return 0 on success or a negative value on failure.
See
.Dv CUSE_ERR_XXX
for known error codes.
.Pp
.Ft "int"
.Fn "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
.Dv CUSE_ERR_XXX
for known error codes.
.Pp
.Ft "struct cuse_dev *"
.Fn "cuse_dev_get_current" "int *pcmd"
This function is used to get the current cuse device pointer and the
currently executing command, by
.Dv CUSE_CMD_XXX
value.
The
.Ar pcmd
argument
is allowed to be
.Dv NULL .
This function should only be used inside the
cuse file operation callbacks.
On success a valid cuse device pointer
is returned.
On failure
.Dv NULL
is returned.
.Pp
.Ft "void"
.Fn "cuse_poll_wakeup" "void"
This function will wake up any file pollers.
.Sh LIBRARY LIMITATIONS
Transfer lengths for
.Fn read ,
.Fn write ,
.Fn cuse_copy_in ,
and
.Fn cuse_copy_out
should not exceed what can fit into a 32-bit signed integer and is
defined by the
.Fn CUSE_LENGTH_MAX
macro.
Transfer lengths for ioctls should not exceed what is defined by the
.Fn CUSE_BUFFER_MAX
macro.
.Sh LIBRARY CALLBACK METHODS
In general fflags are defined by
.Dv CUSE_FFLAG_XXX
and errors are defined by
.Dv CUSE_ERR_XXX .
.Bd -literal -offset indent
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
};
.Ed
.Pp
.Ft "int"
.Fn "cuse_open_t" "struct cuse_dev *" "int fflags"
This function returns a
.Dv CUSE_ERR_XXX
value.
.Pp
.Ft "int"
.Fn "cuse_close_t" "struct cuse_dev *" "int fflags"
This function returns a
.Dv CUSE_ERR_XXX
value.
.Pp
.Ft "int"
.Fn "cuse_read_t" "struct cuse_dev *" "int fflags" "void *peer_ptr" "int len"
This function returns a
.Dv CUSE_ERR_XXX
value in case of failure or the
actually transferred length in case of success.
.Fn cuse_copy_in
and
.Fn cuse_copy_out
must be used to transfer data to and from the
.Ar peer_ptr .
.Pp
.Ft "int"
.Fn "cuse_write_t" "struct cuse_dev *" "int fflags" "const void *peer_ptr" "int len"
This function returns a
.Dv CUSE_ERR_XXX
value in case of failure or the
actually transferred length in case of success.
.Fn cuse_copy_in
and
.Fn cuse_copy_out
must be used to transfer data to and from the
.Ar peer_ptr .
.Pp
.Ft "int"
.Fn "cuse_ioctl_t" "struct cuse_dev *" "int fflags" "unsigned long cmd" "void *peer_data"
This function returns a
.Dv CUSE_ERR_XXX
value in case of failure or zero
in case of success.
.Fn cuse_copy_in
and
.Fn cuse_copy_out
must be used to
transfer data to and from the
.Ar peer_data .
.Pp
.Ft "int"
.Fn "cuse_poll_t" "struct cuse_dev *" "int fflags" "int events"
This function returns a mask of
.Dv CUSE_POLL_XXX
values in case of failure and success.
The events argument is also a mask of
.Dv CUSE_POLL_XXX
values.
.Bd -literal -offset indent
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;
};
.Ed
.Sh HISTORY
.Nm
was written by Hans Petter Selasky.