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MAKE_DEV(9)		 BSD Kernel Developer's	Manual		   MAKE_DEV(9)

     make_dev, make_dev_cred, make_dev_credf, make_dev_alias, destroy_dev,
     destroy_dev_sched,	destroy_dev_sched_cb, destroy_dev_drain, dev_depends
     --	manage cdev's and DEVFS	registration for devices

     #include <sys/param.h>
     #include <sys/conf.h>

     struct cdev *
     make_dev(struct cdevsw *cdevsw, int unit, uid_t uid, gid_t	gid,
	 int perms, const char *fmt, ...);

     struct cdev *
     make_dev_cred(struct cdevsw *cdevsw, int unit, struct ucred *cr,
	 uid_t uid, gid_t gid, int perms, const	char *fmt, ...);

     struct cdev *
     make_dev_credf(int	flags, struct cdevsw *cdevsw, int unit,
	 struct	ucred *cr, uid_t uid, gid_t gid, int perms, const char *fmt,

     struct cdev *
     make_dev_alias(struct cdev	*pdev, const char *fmt,	...);

     destroy_dev(struct	cdev *dev);

     destroy_dev_sched(struct cdev *dev);

     destroy_dev_sched_cb(struct cdev *dev, void (*cb)(void *),	void *arg);

     destroy_dev_drain(struct cdevsw *csw);

     dev_depends(struct	cdev *pdev, struct cdev	*cdev);

     The make_dev_credf() function creates a cdev structure for	a new device.
     It	also notifies devfs(5) of the presence of the new device, that causes
     corresponding nodes to be created.	 Besides this, a devctl(4) notifica-
     tion is sent.  The	device will be owned by	uid, with the group ownership
     as	gid.  The name is the expansion	of fmt and following arguments as
     printf(9) would print it.	The name determines its	path under /dev	or
     other devfs(5) mount point	and may	contain	slash `/' characters to	denote
     subdirectories.  The permissions of the file specified in perms are de-
     fined in <sys/stat.h>:

	   #define S_IRWXU 0000700    /* RWX mask for owner */
	   #define S_IRUSR 0000400    /* R for owner */
	   #define S_IWUSR 0000200    /* W for owner */
	   #define S_IXUSR 0000100    /* X for owner */

	   #define S_IRWXG 0000070    /* RWX mask for group */
	   #define S_IRGRP 0000040    /* R for group */
	   #define S_IWGRP 0000020    /* W for group */
	   #define S_IXGRP 0000010    /* X for group */

	   #define S_IRWXO 0000007    /* RWX mask for other */
	   #define S_IROTH 0000004    /* R for other */
	   #define S_IWOTH 0000002    /* W for other */
	   #define S_IXOTH 0000001    /* X for other */

	   #define S_ISUID 0004000    /* set user id on	execution */
	   #define S_ISGID 0002000    /* set group id on execution */
	   #define S_ISVTX 0001000    /* sticky	bit */
	   #ifndef _POSIX_SOURCE
	   #define S_ISTXT 0001000

     The cr argument specifies credentials that	will be	stored in the si_cred
     member of the initialized struct cdev.  The flags argument	alters the op-
     eration of	make_dev_credf().  The following values	are currently ac-

	   MAKEDEV_REF	   reference the created device
	   MAKEDEV_NOWAIT  do not sleep, may return NULL
	   MAKEDEV_WAITOK  allow the function to sleep to satisfy malloc
	   MAKEDEV_ETERNAL created device will be never	destroyed

     The MAKEDEV_WAITOK	flag is	assumed	if none	of MAKEDEV_WAITOK,
     MAKEDEV_NOWAIT is specified.

     The dev_clone(9) event handler shall specify MAKEDEV_REF flag when	creat-
     ing a device in response to lookup, to avoid race where the device	cre-
     ated is destroyed immediately after devfs_lookup(9) drops his reference
     to	cdev.

     The MAKEDEV_ETERNAL flag allows the kernel	to not acquire some locks when
     translating system	calls into the cdevsw methods calls.  It is responsi-
     bility of the driver author to make sure that destroy_dev() is never
     called on the returned cdev.  For the convenience,	use the
     MAKEDEV_ETERNAL_KLD flag for the code that	can be compiled	into kernel or
     loaded (and unloaded) as loadable module.

     The make_dev_cred() function is equivalent	to the call

	   make_dev_credf(0, cdevsw, unit, cr, uid, gid, perms,	fmt, ...);

     The make_dev() function call is the same as

	   make_dev_credf(0, cdevsw, unit, NULL, uid, gid, perms, fmt, ...);

     The make_dev_alias() function takes the returned cdev from	make_dev() and
     makes another (aliased) name for this device.  It is an error to call
     make_dev_alias() prior to calling make_dev().

     The cdev returned by make_dev() and make_dev_alias() has two fields,
     si_drv1 and si_drv2, that are available to	store state.  Both fields are
     of	type void *.  These are	designed to replace the	unit argument to
     make_dev(), which can be obtained with dev2unit().

     The destroy_dev() function	takes the returned cdev	from make_dev()	and
     destroys the registration for that	device.	 The notification is sent to
     devctl(4) about the destruction event.  Do	not call destroy_dev() on de-
     vices that	were created with make_dev_alias().

     The dev_depends() function	establishes a parent-child relationship	be-
     tween two devices.	 The net effect	is that	a destroy_dev()	of the parent
     device will also result in	the destruction	of the child device(s),	if any
     exist.  A device may simultaneously be a parent and a child, so it	is
     possible to build a complete hierarchy.

     The destroy_dev_sched_cb()	function schedules execution of	the
     destroy_dev() for the specified cdev in the safe context.	After
     destroy_dev() is finished,	and if the supplied cb is not NULL, the	call-
     back cb is	called,	with argument arg.  The	destroy_dev_sched() function
     is	the same as

	   destroy_dev_sched(cdev, NULL, NULL);

     The d_close() driver method cannot	call destroy_dev() directly. Doing so
     causes deadlock when destroy_dev()	waits for all threads to leave the
     driver methods.  Also, because destroy_dev() sleeps, no non-sleepable
     locks may be held over the	call.  The destroy_dev_sched() family of func-
     tions overcome these issues.

     The device	driver may call	the destroy_dev_drain()	function to wait until
     all devices that have supplied csw	as cdevsw, are destroyed. This is use-
     ful when driver knows that	destroy_dev_sched() is called for all instan-
     tiated devices, but need to postpone module unload	until destroy_dev() is
     actually finished for all of them.

     devctl(4),	destroy_dev_drain(9), dev_clone(9), devfs(5)

     The make_dev() and	destroy_dev() functions	first appeared in FreeBSD 4.0.
     The function make_dev_alias() first appeared in FreeBSD 4.1.  The func-
     tion dev_depends()	first appeared in FreeBSD 5.0.	The functions
     make_dev_credf(), destroy_dev_sched(), destroy_dev_sched_cb() first ap-
     peared in FreeBSD 7.0.

BSD			       September 5, 2010			   BSD


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