1 ==============================================
2 Block layer support for Persistent Reservation
3 ==============================================
4
5 The Linux kernel supports a user space interfa
6 Persistent Reservations which map to block dev
7 these (like SCSI). Persistent Reservations all
8 access to block devices to specific initiators
9 setup.
10
11 This document gives a general overview of the
12 For a more detailed reference please refer to
13 Commands standard, specifically the section on
14 "PERSISTENT RESERVE IN" and "PERSISTENT RESERV
15
16 All implementations are expected to ensure the
17 a power loss and cover all connections in a mu
18 These behaviors are optional in SPC but will b
19 by Linux.
20
21
22 The following types of reservations are suppor
23 ----------------------------------------------
24
25 - PR_WRITE_EXCLUSIVE
26 Only the initiator that owns the reser
27 device. Any initiator can read from t
28
29 - PR_EXCLUSIVE_ACCESS
30 Only the initiator that owns the reser
31 device.
32
33 - PR_WRITE_EXCLUSIVE_REG_ONLY
34 Only initiators with a registered key
35 Any initiator can read from the device
36
37 - PR_EXCLUSIVE_ACCESS_REG_ONLY
38 Only initiators with a registered key
39
40 - PR_WRITE_EXCLUSIVE_ALL_REGS
41
42 Only initiators with a registered key
43 Any initiator can read from the device
44 All initiators with a registered key a
45 holders.
46 Please reference the SPC spec on the m
47 holder if you want to use this type.
48
49 - PR_EXCLUSIVE_ACCESS_ALL_REGS
50 Only initiators with a registered key
51 All initiators with a registered key a
52 holders.
53 Please reference the SPC spec on the m
54 holder if you want to use this type.
55
56
57 The following ioctl are supported:
58 ----------------------------------
59
60 1. IOC_PR_REGISTER
61 ^^^^^^^^^^^^^^^^^^
62
63 This ioctl command registers a new reservation
64 is non-null. If no existing reservation exist
65 if an existing reservation should be replaced
66 the old reservation key.
67
68 If the new_key argument is 0 it unregisters th
69 in old_key.
70
71
72 2. IOC_PR_RESERVE
73 ^^^^^^^^^^^^^^^^^
74
75 This ioctl command reserves the device and thu
76 devices based on the type argument. The key a
77 reservation key for the device as acquired by
78 IOC_PR_REGISTER_IGNORE, IOC_PR_PREEMPT or IOC_
79
80
81 3. IOC_PR_RELEASE
82 ^^^^^^^^^^^^^^^^^
83
84 This ioctl command releases the reservation sp
85 and thus removes any access restriction implie
86
87
88 4. IOC_PR_PREEMPT
89 ^^^^^^^^^^^^^^^^^
90
91 This ioctl command releases the existing reser
92 old_key and replaces it with a new reservation
93 reservation key new_key.
94
95
96 5. IOC_PR_PREEMPT_ABORT
97 ^^^^^^^^^^^^^^^^^^^^^^^
98
99 This ioctl command works like IOC_PR_PREEMPT e
100 any outstanding command sent over a connection
101
102 6. IOC_PR_CLEAR
103 ^^^^^^^^^^^^^^^
104
105 This ioctl command unregisters both key and an
106 registered with the device and drops any exist
107
108
109 Flags
110 -----
111
112 All the ioctls have a flag field. Currently o
113
114 - PR_FL_IGNORE_KEY
115 Ignore the existing reservation key.
116 IOC_PR_REGISTER, and some implementati
117 IOC_PR_RESERVE.
118
119 For all unknown flags the kernel will return -
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