From bbd3e064362e5057cc4799ba2e4d68c7593e490b Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Thu, 15 Oct 2015 14:10:48 +0200 Subject: block: add an API for Persistent Reservations This commits adds a driver API and ioctls for controlling Persistent Reservations s/genericly/generically/ at the block layer. Persistent Reservations are supported by SCSI and NVMe and allow controlling who gets access to a device in a shared storage setup. Note that we add a pr_ops structure to struct block_device_operations instead of adding the members directly to avoid bloating all instances of devices that will never support Persistent Reservations. Signed-off-by: Christoph Hellwig Signed-off-by: Jens Axboe --- Documentation/block/pr.txt | 119 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 119 insertions(+) create mode 100644 Documentation/block/pr.txt (limited to 'Documentation/block') diff --git a/Documentation/block/pr.txt b/Documentation/block/pr.txt new file mode 100644 index 000000000000..d3eb1ca65051 --- /dev/null +++ b/Documentation/block/pr.txt @@ -0,0 +1,119 @@ + +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. -- cgit v1.2.3