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);
int
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 userland, 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 -1. The
devname,
major number, and device type (character or block) must correspond to the
device file which will be opened by user programs. By passing
-1 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 structures. devsw_detach()
should be called before a loaded device driver is unloaded.
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()
and devsw_detach() return 0. Otherwise they return
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.