destroy_dev(9) manage

Other Alias

make_dev, make_dev_cred, make_dev_credf, make_dev_p, make_dev_alias, make_dev_alias_p, destroy_dev_sched, destroy_dev_sched_cb, destroy_dev_drain, dev_depends


In sys/param.h In sys/conf.h Ft struct cdev * Fn make_dev struct cdevsw *cdevsw int unit uid_t uid gid_t gid int perms const char *fmt ... Ft struct cdev * Fn make_dev_cred struct cdevsw *cdevsw int unit struct ucred *cr uid_t uid gid_t gid int perms const char *fmt ... Ft struct cdev * Fn make_dev_credf int flags struct cdevsw *cdevsw int unit struct ucred *cr uid_t uid gid_t gid int perms const char *fmt ... Ft int Fn make_dev_p int flags struct cdev **cdev struct cdevsw *devsw struct ucred *cr uid_t uid gid_t gid int mode const char *fmt ... Ft struct cdev * Fn make_dev_alias struct cdev *pdev const char *fmt ... Ft int Fn make_dev_alias_p int flags struct cdev **cdev struct cdev *pdev const char *fmt ... Ft void Fn destroy_dev struct cdev *dev Ft void Fn destroy_dev_sched struct cdev *dev Ft void Fn destroy_dev_sched_cb struct cdev *dev void (*cb)(void *) void *arg Ft void Fn destroy_dev_drain struct cdevsw *csw Ft void Fn dev_depends struct cdev *pdev struct cdev *cdev


The Fn make_dev_credf function creates a Fa 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) notification 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 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 */
#define S_ISTXT 0001000

The cr argument specifies credentials that will be stored in the Fa si_cred member of the initialized Fa struct cdev . The flags argument alters the operation of Fn make_dev_credf or Fn make_dev_p . The following values are currently accepted:

reference the created device
do not sleep, the call may fail
allow the function to sleep to satisfy malloc
created device will be never destroyed
return an error if the device name is invalid or already exists

Only MAKEDEV_NOWAIT MAKEDEV_WAITOK and MAKEDEV_CHECKNAME values are accepted for the Fn make_dev_alias_p function.

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

The dev_clone9 event handler shall specify MAKEDEV_REF flag when creating a device in response to lookup, to avoid race where the device created is destroyed immediately after devfs_lookup9 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 responsibility of the driver author to make sure that Fn 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.

A panic will occur if the MAKEDEV_CHECKNAME flag is not specified and the device name is invalid or already exists.

The Fn make_dev_cred function is equivalent to the call

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

The Fn make_dev function call is the same as

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

The Fn make_dev_p function is similar to Fn make_dev_credf but it may return an error number and takes a pointer to the resulting Ft *cdev as an argument.

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

Fn make_dev_alias_p function is similar to Fn make_dev_alias but it takes a pointer to the resulting Ft *cdev as an argument and may return an error.

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

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

The Fn dev_depends function establishes a parent-child relationship between two devices. The net effect is that a Fn 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 Fn destroy_dev_sched_cb function schedules execution of the Fn destroy_dev for the specified Fa cdev in the safe context. After Fn destroy_dev is finished, and if the supplied Fa cb is not NULL the callback Fa cb is called, with argument Fa arg . The Fn destroy_dev_sched function is the same as

destroy_dev_sched_cb(cdev, NULL, NULL);

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

The device driver may call the Fn destroy_dev_drain function to wait until all devices that have supplied Fa csw as cdevsw, are destroyed. This is useful when driver knows that Fn destroy_dev_sched is called for all instantiated devices, but need to postpone module unload until Fn destroy_dev is actually finished for all of them.


If successful, Fn make_dev_p will return 0, otherwise it will return an error. If successful, Fn make_dev_credf will return a valid Fa cdev pointer, otherwise it will return NULL


The Fn make_dev_p and Fn make_dev_alias_p call will fail and the device will be not registered if:

The MAKEDEV_NOWAIT flag was specified and a memory allocation request could not be satisfied.
The MAKEDEV_CHECKNAME flag was specified and the provided device name is longer than SPECNAMELEN
The MAKEDEV_CHECKNAME flag was specified and the provided device name is empty, contains a Qq . or Qq .. path component or ends with `/'
The MAKEDEV_CHECKNAME flag was specified and the provided device name contains invalid characters.
The MAKEDEV_CHECKNAME flag was specified and the provided device name already exists.


The Fn make_dev and Fn destroy_dev functions first appeared in Fx 4.0 . The function Fn make_dev_alias first appeared in Fx 4.1 . The function Fn dev_depends first appeared in Fx 5.0 . The functions Fn make_dev_credf , Fn destroy_dev_sched , Fn destroy_dev_sched_cb first appeared in Fx 7.0 . The function Fn make_dev_p first appeared in Fx 8.2 .