Based on kernel version 4.16.1. Page generated on 2018-04-09 11:52 EST.
1 2 Block layer support for Persistent Reservations 3 =============================================== 4 5 The Linux kernel supports a user space interface for simplified 6 Persistent Reservations which map to block devices that support 7 these (like SCSI). Persistent Reservations allow restricting 8 access to block devices to specific initiators in a shared storage 9 setup. 10 11 This document gives a general overview of the support ioctl commands. 12 For a more detailed reference please refer the the SCSI Primary 13 Commands standard, specifically the section on Reservations and the 14 "PERSISTENT RESERVE IN" and "PERSISTENT RESERVE OUT" commands. 15 16 All implementations are expected to ensure the reservations survive 17 a power loss and cover all connections in a multi path environment. 18 These behaviors are optional in SPC but will be automatically applied 19 by Linux. 20 21 22 The following types of reservations are supported: 23 -------------------------------------------------- 24 25 - PR_WRITE_EXCLUSIVE 26 27 Only the initiator that owns the reservation can write to the 28 device. Any initiator can read from the device. 29 30 - PR_EXCLUSIVE_ACCESS 31 32 Only the initiator that owns the reservation can access the 33 device. 34 35 - PR_WRITE_EXCLUSIVE_REG_ONLY 36 37 Only initiators with a registered key can write to the device, 38 Any initiator can read from the device. 39 40 - PR_EXCLUSIVE_ACCESS_REG_ONLY 41 42 Only initiators with a registered key can access the device. 43 44 - PR_WRITE_EXCLUSIVE_ALL_REGS 45 46 Only initiators with a registered key can write to the device, 47 Any initiator can read from the device. 48 All initiators with a registered key are considered reservation 49 holders. 50 Please reference the SPC spec on the meaning of a reservation 51 holder if you want to use this type. 52 53 - PR_EXCLUSIVE_ACCESS_ALL_REGS 54 55 Only initiators with a registered key can access the device. 56 All initiators with a registered key are considered reservation 57 holders. 58 Please reference the SPC spec on the meaning of a reservation 59 holder if you want to use this type. 60 61 62 The following ioctl are supported: 63 ---------------------------------- 64 65 1. IOC_PR_REGISTER 66 67 This ioctl command registers a new reservation if the new_key argument 68 is non-null. If no existing reservation exists old_key must be zero, 69 if an existing reservation should be replaced old_key must contain 70 the old reservation key. 71 72 If the new_key argument is 0 it unregisters the existing reservation passed 73 in old_key. 74 75 76 2. IOC_PR_RESERVE 77 78 This ioctl command reserves the device and thus restricts access for other 79 devices based on the type argument. The key argument must be the existing 80 reservation key for the device as acquired by the IOC_PR_REGISTER, 81 IOC_PR_REGISTER_IGNORE, IOC_PR_PREEMPT or IOC_PR_PREEMPT_ABORT commands. 82 83 84 3. IOC_PR_RELEASE 85 86 This ioctl command releases the reservation specified by key and flags 87 and thus removes any access restriction implied by it. 88 89 90 4. IOC_PR_PREEMPT 91 92 This ioctl command releases the existing reservation referred to by 93 old_key and replaces it with a new reservation of type for the 94 reservation key new_key. 95 96 97 5. IOC_PR_PREEMPT_ABORT 98 99 This ioctl command works like IOC_PR_PREEMPT except that it also aborts 100 any outstanding command sent over a connection identified by old_key. 101 102 6. IOC_PR_CLEAR 103 104 This ioctl command unregisters both key and any other reservation key 105 registered with the device and drops any existing reservation. 106 107 108 Flags 109 ----- 110 111 All the ioctls have a flag field. Currently only one flag is supported: 112 113 - PR_FL_IGNORE_KEY 114 115 Ignore the existing reservation key. This is commonly supported for 116 IOC_PR_REGISTER, and some implementation may support the flag for 117 IOC_PR_RESERVE. 118 119 For all unknown flags the kernel will return -EOPNOTSUPP.