Writing Device Drivers

cb_ops Structure

	int		(*cb_open)(dev_t *devp, int flag, int otyp,
 				cred_t *credp);
 	int		(*cb_close)(dev_t dev, int flag, int otyp,
 				cred_t *credp);
 	int		(*cb_strategy)(struct buf *bp);
 	int		(*cb_print)(dev_t dev, char *str);
 	int		(*cb_dump)(dev_t dev, caddr_t addr, daddr_t blkno,
 				int nblk);
 	int		(*cb_read)(dev_t dev, struct uio *uiop, cred_t *credp);
 	int		(*cb_write)(dev_t dev, struct uio *uiop, cred_t *credp);
 	int		(*cb_ioctl)(dev_t dev, int cmd, intptr_t arg, int mode,
 				cred_t *credp, int *rvalp);
 	int		(*cb_devmap)(dev_t dev, devmap_cookie_t dhp,
 				offset_t off, size_t len, size_t *maplen,
 				uint_t model);
 	int		(*cb_mmap)(dev_t dev, off_t off, int prot);
 	int		(*cb_segmap)(dev_t dev, off_t off, struct as *asp,
 				addr_t *addrp, off_t len, unsigned int prot,
 				unsigned int maxprot, unsigned int flags,
 				cred_t *credp);
 	int		(*cb_chpoll)(dev_t dev, short events, int anyyet,
 				short *reventsp, struct pollhead **phpp);
 	int		(*cb_prop_op)(dev_t dev, dev_info_t *dip,
 				ddi_prop_op_t prop_op, int mod_flags,
 				char *name, caddr_t valuep, int *length);
 	struct streamtab					*cb_str;   /* STREAMS information */
 	int		cb_flag;
 	int		cb_rev;
 	int		(*cb_aread)(dev_t dev, struct aio_req *aio,
 				cred_t *credp);
 	int		(*cb_awrite)(dev_t dev, struct aio_req *aio,
 				cred_t *credp);

The cb_ops(9S) structure contains the entry points for the character and block operations of the device driver. Any entry points the driver does not support should be initialized to nodev(9F). For example, character device drivers should set all the block-only fields (such as cb_stategy to nodev(9F)). Note that the mmap(9E) entry point is maintained for compatibility with previous releases, and drivers should use the devmap(9E) entry point for device memory mapping. If devmap(9E) is supported, set mmap(9E) to nodev(9F).

The cb_str field is used to determine if this is a STREAMS-based driver. The device drivers discussed in this book are not STREAMS based. For a non-STREAMS-based driver, cb_str must be set to NULL.

The cb_flag member contains the following flags:

cb_rev is the cb_ops(9S) structure revision number. This field must be set to CB_REV.