1 USB Anchors 2 ~~~~~~~~~~~ 3 4 What is anchor? 5 =============== 6 7 A USB driver needs to support some callbacks requiring 8 a driver to cease all IO to an interface. To do so, a 9 driver has to keep track of the URBs it has submitted 10 to know they've all completed or to call usb_kill_urb 11 for them. The anchor is a data structure takes care of 12 keeping track of URBs and provides methods to deal with 13 multiple URBs. 14 15 Allocation and Initialisation 16 ============================= 17 18 There's no API to allocate an anchor. It is simply declared 19 as struct usb_anchor. :c:func:`init_usb_anchor` must be called to 20 initialise the data structure. 21 22 Deallocation 23 ============ 24 25 Once it has no more URBs associated with it, the anchor can be 26 freed with normal memory management operations. 27 28 Association and disassociation of URBs with anchors 29 =================================================== 30 31 An association of URBs to an anchor is made by an explicit 32 call to :c:func:`usb_anchor_urb`. The association is maintained until 33 an URB is finished by (successful) completion. Thus disassociation 34 is automatic. A function is provided to forcibly finish (kill) 35 all URBs associated with an anchor. 36 Furthermore, disassociation can be made with :c:func:`usb_unanchor_urb` 37 38 Operations on multitudes of URBs 39 ================================ 40 41 :c:func:`usb_kill_anchored_urbs` 42 -------------------------------- 43 44 This function kills all URBs associated with an anchor. The URBs 45 are called in the reverse temporal order they were submitted. 46 This way no data can be reordered. 47 48 :c:func:`usb_unlink_anchored_urbs` 49 ---------------------------------- 50 51 52 This function unlinks all URBs associated with an anchor. The URBs 53 are processed in the reverse temporal order they were submitted. 54 This is similar to :c:func:`usb_kill_anchored_urbs`, but it will not sleep. 55 Therefore no guarantee is made that the URBs have been unlinked when 56 the call returns. They may be unlinked later but will be unlinked in 57 finite time. 58 59 :c:func:`usb_scuttle_anchored_urbs` 60 ----------------------------------- 61 62 All URBs of an anchor are unanchored en masse. 63 64 :c:func:`usb_wait_anchor_empty_timeout` 65 --------------------------------------- 66 67 This function waits for all URBs associated with an anchor to finish 68 or a timeout, whichever comes first. Its return value will tell you 69 whether the timeout was reached. 70 71 :c:func:`usb_anchor_empty` 72 -------------------------- 73 74 Returns true if no URBs are associated with an anchor. Locking 75 is the caller's responsibility. 76 77 :c:func:`usb_get_from_anchor` 78 ----------------------------- 79 80 Returns the oldest anchored URB of an anchor. The URB is unanchored 81 and returned with a reference. As you may mix URBs to several 82 destinations in one anchor you have no guarantee the chronologically 83 first submitted URB is returned.
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