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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
     defined 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
     operation of make_dev_credf().  The following values are currently

	   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
     devices that were created with make_dev_alias().

     The dev_depends() function establishes a parent-child relationship
     between two devices.  The net effect is that a destroy_dev() of the par‐
     ent 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
     appeared in FreeBSD 7.0.

BSD			       September 5, 2010			   BSD

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