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HOTPLUG(4)               BSD Kernel Interfaces Manual               HOTPLUG(4)

     hotplug -- devices hot plugging

     pseudo-device hotplug 1

     #include <&lt;sys/types.h>&gt;
     #include <&lt;sys/device.h>&gt;
     #include <&lt;sys/hotplug.h>&gt;

     The hotplug pseudo-device passes device attachment and detachment events
     to userland.  When a device attaches or detaches, the corresponding event
     is queued.  The events can then be obtained from the queue through the
     read(2) call on the /dev/hotplug device file.  Once an event has been
     read, it's deleted from the queue.  The event queue has a limited size
     and if it's full all new events will be dropped.  Each event is described
     with the following structure declared in the <sys/hotplug.h> header file:

           struct hotplug_event {
                   int             he_type;        /* event type           */
                   enum devclass   he_devclass;    /* device class         */
                   char            he_devname[16]; /* device name          */

     The he_type field describes the event type and can be either
     HOTPLUG_DEVAT for device attachment or HOTPLUG_DEVDT for detachment.  The
     he_devclass field describes the device class.  All device classes can be
     found in the <sys/device.h> header file:

           enum devclass {
                   DV_DULL,        /* generic, no special info */
                   DV_CPU,         /* CPU (carries resource utilization) */
                   DV_DISK,        /* disk drive (label, etc) */
                   DV_IFNET,       /* network interface */
                   DV_TAPE,        /* tape device */
                   DV_TTY          /* serial line interface */

     The he_devname is a device name including unit number, e.g. sd1.

     Only one structure can be read per call.  If there are no events in the
     queue, the read(2) call will block until an event appears.

     hotplug: event lost, queue full  New events will be dropped until all
     pending events have been read.

     read(2), hotplugd(8)

     The hotplug device first appeared in OpenBSD 3.6.

     The hotplug driver was written by Alexander Yurchenko

BSD                            January 21, 2014                            BSD