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authorLinus Torvalds <torvalds@linux-foundation.org>2015-11-04 21:01:27 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-11-04 21:01:27 -0800
commitccf21b69a83afaee4d5499e0d03eacf23946e08c (patch)
tree9831589f82e8d5a47eac253f54f4121e62e4c5a6 /Documentation
parent527d1529e38b36fd22e65711b653ab773179d9e8 (diff)
parent73fcf4e20ebd19468b3ad033be93582258435462 (diff)
Merge branch 'for-4.4/reservations' of git://git.kernel.dk/linux-block
Pull block reservation support from Jens Axboe: "This adds support for persistent reservations, both at the core level, as well as for sd and NVMe" [ Background from the docs: "Persistent Reservations allow restricting access to block devices to specific initiators in a shared storage setup. All implementations are expected to ensure the reservations survive a power loss and cover all connections in a multi path environment" ] * 'for-4.4/reservations' of git://git.kernel.dk/linux-block: NVMe: Precedence error in nvme_pr_clear() nvme: add missing endianess annotations in nvme_pr_command NVMe: Add persistent reservation ops sd: implement the Persistent Reservation API block: add an API for Persistent Reservations block: cleanup blkdev_ioctl
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+
+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
+ holder if you want to use this type.
+
+ - 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
+ holder if you want to use this type.
+
+
+The following ioctl are supported:
+----------------------------------
+
+1. IOC_PR_REGISTER
+
+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
+
+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
+
+This ioctl command releases the reservation specified by key and flags
+and thus removes any access restriction implied by it.
+
+
+4. IOC_PR_PREEMPT
+
+This ioctl command releases the existing reservation referred to by
+old_key and replaces it with a a new reservation of type for the
+reservation key new_key.
+
+
+5. IOC_PR_PREEMPT_ABORT
+
+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
+
+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.