devsw(9) - NetBSD Manual Pages

DEVSW(9)               NetBSD Kernel Developer's Manual               DEVSW(9)


NAME

     devsw, devsw_attach, devsw_detach, bdevsw_lookup, cdevsw_lookup,
     bdevsw_lookup_major, cdevsw_lookup_major -- character and block device
     switch functions


SYNOPSIS

     #include <sys/conf.h>

     int
     devsw_attach(const char *devname, const struct bdevsw *bev,
         devmajor_t *bmajor, const struct cdevsw *cdev, devmajor_t *cmajor);

     void
     devsw_detach(const struct bdevsw *bdev, const struct cdevsw *cdev);

     const struct bdevsw *
     bdevsw_lookup(dev_t dev);

     const struct cdevsw *
     cdevsw_lookup(dev_t dev);

     devmajor_t
     bdevsw_lookup_major(const struct bdevsw *bdev);

     devmajor_t
     cdevsw_lookup_major(const struct cdevsw *cdev);


DESCRIPTION

     If a device driver has character device interfaces accessed from user-
     land, the driver must define a cdevsw structure.  If the driver also has
     block device interfaces, the driver must additionally define a bdevsw
     structure.  These structures are constant, and are defined within the
     driver(9).

     For drivers which are included in the kernel via config(1), the cdevsw
     and bdevsw structures are automatically linked into the configuration
     database.  For drivers which are separately loaded, the devsw_attach()
     function creates the necessary linkage and associates the cdev and
     optional bdev with the driver(9).  If there is no block device interface
     needed, bdev should be set to NULL and bmajor to NODEVMAJOR.  The
     devname, major number, and device type (character or block) must corre-
     spond to the device file which will be opened by user programs.  By pass-
     ing NODEVMAJOR to the function for the cmajor or bmajor, the major number
     can be automatically generated.  It can then be returned to userspace
     (for example, using sysctl(8)) for creation of the device node.

     The devsw_detach() function is used to detach the bdev and cdev struc-
     tures.  devsw_detach() should be called before a loaded device driver is
     unloaded.  The caller must ensure that there are no open instances of the
     device, and that the device's d_open function will fail, before calling
     devsw_detach().

     The bdevsw_lookup() and cdevsw_lookup() functions return const struct
     bdevsw * and const struct cdevsw * for the given dev.

     The bdevsw_lookup_major() and cdevsw_lookup_major() functions return
     devmajor_t for the given const struct bdevsw * or const struct cdevsw *.


RETURN VALUES

     Upon successful completion, devsw_attach() returns 0.  Otherwise it
     returns an error value.

     In case of failure, bdevsw_lookup() and cdevsw_lookup() return the NULL
     value.

     The bdevsw_lookup_major() and cdevsw_lookup_major() functions return
     NODEVMAJOR for an unsuccessful completion.


SEE ALSO

     driver(9)

NetBSD 10.99                   February 2, 2023                   NetBSD 10.99