freebsd man page for devfs_set_cdevpriv

DEVFS_CDEVPRIV(9)					   BSD Kernel Developer's Manual					 DEVFS_CDEVPRIV(9)

NAME
     devfs_set_cdevpriv, devfs_get_cdevpriv, devfs_clear_cdevpriv -- manage per-open filedescriptor data for devices

SYNOPSIS
     #include <sys/param.h>
     #include <sys/conf.h>

     typedef void (*cdevpriv_dtr_t)(void *data);

     int
     devfs_get_cdevpriv(void **datap);

     int
     devfs_set_cdevpriv(void *priv, cdevpriv_dtr_t dtr);

     void
     devfs_clear_cdevpriv(void);

DESCRIPTION
     The devfs_xxx_cdevpriv() family of functions allows the cdev driver methods to associate some driver-specific data with each user process
     open(2) of the device special file.  Currently, functioning of these functions is restricted to the context of the cdevsw switch method calls
     performed as devfs(5) operations in response to system calls that use filedescriptors.

     The devfs_set_cdevpriv() function associates a data pointed by priv with current calling context (filedescriptor).  The data may be retrieved
     later, possibly from another call performed on this filedescriptor, by the devfs_get_cdevpriv() function.	The devfs_clear_cdevpriv() disas-
     sociates previously attached data from context.  Immediately after devfs_clear_cdevpriv() finished operating, the dtr callback is called,
     with private data supplied data argument.	The devfs_clear_cdevpriv() function will be also be called if the open callback function returns
     an error code.

     On the last filedescriptor close, system automatically arranges devfs_clear_cdevpriv() call.

     If successful, the functions return 0.

     The function devfs_set_cdevpriv() returns the following values on error:

     [ENOENT]		The current call is not associated with some filedescriptor.

     [EBUSY]		The private driver data is already associated with current filedescriptor.

     The function devfs_get_cdevpriv() returns the following values on error:

     [EBADF]		The current call is not associated with some filedescriptor.

     [ENOENT]		The private driver data was not associated with current filedescriptor, or devfs_clear_cdevpriv() was called.

SEE ALSO
     close(2), open(2), devfs(5), kern_openat(9)

HISTORY
     The devfs_cdevpriv() family of functions first appeared in FreeBSD 7.1.

BSD
								  August 15, 2012							       BSD