2019-04-18 22:45:00 +00:00
|
|
|
===============================================
|
2015-10-15 12:10:48 +00:00
|
|
|
Block layer support for Persistent Reservations
|
|
|
|
===============================================
|
|
|
|
|
|
|
|
The Linux kernel supports a user space interface for simplified
|
|
|
|
Persistent Reservations which map to block devices that support
|
|
|
|
these (like SCSI). Persistent Reservations allow restricting
|
|
|
|
access to block devices to specific initiators in a shared storage
|
|
|
|
setup.
|
|
|
|
|
|
|
|
This document gives a general overview of the support ioctl commands.
|
|
|
|
For a more detailed reference please refer the the SCSI Primary
|
|
|
|
Commands standard, specifically the section on Reservations and the
|
|
|
|
"PERSISTENT RESERVE IN" and "PERSISTENT RESERVE OUT" commands.
|
|
|
|
|
|
|
|
All implementations are expected to ensure the reservations survive
|
|
|
|
a power loss and cover all connections in a multi path environment.
|
|
|
|
These behaviors are optional in SPC but will be automatically applied
|
|
|
|
by Linux.
|
|
|
|
|
|
|
|
|
|
|
|
The following types of reservations are supported:
|
|
|
|
--------------------------------------------------
|
|
|
|
|
|
|
|
- PR_WRITE_EXCLUSIVE
|
|
|
|
Only the initiator that owns the reservation can write to the
|
|
|
|
device. Any initiator can read from the device.
|
|
|
|
|
|
|
|
- PR_EXCLUSIVE_ACCESS
|
|
|
|
Only the initiator that owns the reservation can access the
|
|
|
|
device.
|
|
|
|
|
|
|
|
- PR_WRITE_EXCLUSIVE_REG_ONLY
|
|
|
|
Only initiators with a registered key can write to the device,
|
|
|
|
Any initiator can read from the device.
|
|
|
|
|
|
|
|
- PR_EXCLUSIVE_ACCESS_REG_ONLY
|
|
|
|
Only initiators with a registered key can access the device.
|
|
|
|
|
|
|
|
- PR_WRITE_EXCLUSIVE_ALL_REGS
|
|
|
|
|
|
|
|
Only initiators with a registered key can write to the device,
|
|
|
|
Any initiator can read from the device.
|
|
|
|
All initiators with a registered key are considered reservation
|
|
|
|
holders.
|
|
|
|
Please reference the SPC spec on the meaning of a reservation
|
2019-04-18 22:45:00 +00:00
|
|
|
holder if you want to use this type.
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
- PR_EXCLUSIVE_ACCESS_ALL_REGS
|
|
|
|
Only initiators with a registered key can access the device.
|
|
|
|
All initiators with a registered key are considered reservation
|
|
|
|
holders.
|
|
|
|
Please reference the SPC spec on the meaning of a reservation
|
2019-04-18 22:45:00 +00:00
|
|
|
holder if you want to use this type.
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
|
|
|
|
The following ioctl are supported:
|
|
|
|
----------------------------------
|
|
|
|
|
|
|
|
1. IOC_PR_REGISTER
|
2019-04-18 22:45:00 +00:00
|
|
|
^^^^^^^^^^^^^^^^^^
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
This ioctl command registers a new reservation if the new_key argument
|
|
|
|
is non-null. If no existing reservation exists old_key must be zero,
|
|
|
|
if an existing reservation should be replaced old_key must contain
|
|
|
|
the old reservation key.
|
|
|
|
|
|
|
|
If the new_key argument is 0 it unregisters the existing reservation passed
|
|
|
|
in old_key.
|
|
|
|
|
|
|
|
|
|
|
|
2. IOC_PR_RESERVE
|
2019-04-18 22:45:00 +00:00
|
|
|
^^^^^^^^^^^^^^^^^
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
This ioctl command reserves the device and thus restricts access for other
|
|
|
|
devices based on the type argument. The key argument must be the existing
|
|
|
|
reservation key for the device as acquired by the IOC_PR_REGISTER,
|
|
|
|
IOC_PR_REGISTER_IGNORE, IOC_PR_PREEMPT or IOC_PR_PREEMPT_ABORT commands.
|
|
|
|
|
|
|
|
|
|
|
|
3. IOC_PR_RELEASE
|
2019-04-18 22:45:00 +00:00
|
|
|
^^^^^^^^^^^^^^^^^
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
This ioctl command releases the reservation specified by key and flags
|
|
|
|
and thus removes any access restriction implied by it.
|
|
|
|
|
|
|
|
|
|
|
|
4. IOC_PR_PREEMPT
|
2019-04-18 22:45:00 +00:00
|
|
|
^^^^^^^^^^^^^^^^^
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
This ioctl command releases the existing reservation referred to by
|
2017-01-24 12:45:15 +00:00
|
|
|
old_key and replaces it with a new reservation of type for the
|
2015-10-15 12:10:48 +00:00
|
|
|
reservation key new_key.
|
|
|
|
|
|
|
|
|
|
|
|
5. IOC_PR_PREEMPT_ABORT
|
2019-04-18 22:45:00 +00:00
|
|
|
^^^^^^^^^^^^^^^^^^^^^^^
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
This ioctl command works like IOC_PR_PREEMPT except that it also aborts
|
|
|
|
any outstanding command sent over a connection identified by old_key.
|
|
|
|
|
|
|
|
6. IOC_PR_CLEAR
|
2019-04-18 22:45:00 +00:00
|
|
|
^^^^^^^^^^^^^^^
|
2015-10-15 12:10:48 +00:00
|
|
|
|
|
|
|
This ioctl command unregisters both key and any other reservation key
|
|
|
|
registered with the device and drops any existing reservation.
|
|
|
|
|
|
|
|
|
|
|
|
Flags
|
|
|
|
-----
|
|
|
|
|
|
|
|
All the ioctls have a flag field. Currently only one flag is supported:
|
|
|
|
|
|
|
|
- PR_FL_IGNORE_KEY
|
|
|
|
Ignore the existing reservation key. This is commonly supported for
|
|
|
|
IOC_PR_REGISTER, and some implementation may support the flag for
|
|
|
|
IOC_PR_RESERVE.
|
|
|
|
|
|
|
|
For all unknown flags the kernel will return -EOPNOTSUPP.
|