DEVSW(9)

DEVSW(9) | 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);
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.

# SEE ALSO

driver(9)

April 30, 2017 | NetBSD 8.3