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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() disassociates previously attached data from context.  Immediately
     after devfs_clear_cdevpriv() finished operating, the dtr callback is called, with private
     data supplied data argument.

     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

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

HISTORY

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