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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 | ||
=============================================== | ||
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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. | ||
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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. | ||
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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. | ||
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The following types of reservations are supported: | ||
-------------------------------------------------- | ||
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- PR_WRITE_EXCLUSIVE | ||
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Only the initiator that owns the reservation can write to the | ||
device. Any initiator can read from the device. | ||
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- PR_EXCLUSIVE_ACCESS | ||
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Only the initiator that owns the reservation can access the | ||
device. | ||
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- PR_WRITE_EXCLUSIVE_REG_ONLY | ||
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Only initiators with a registered key can write to the device, | ||
Any initiator can read from the device. | ||
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- PR_EXCLUSIVE_ACCESS_REG_ONLY | ||
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Only initiators with a registered key can access the device. | ||
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- PR_WRITE_EXCLUSIVE_ALL_REGS | ||
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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. | ||
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- PR_EXCLUSIVE_ACCESS_ALL_REGS | ||
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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. | ||
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The following ioctl are supported: | ||
---------------------------------- | ||
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1. IOC_PR_REGISTER | ||
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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. | ||
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If the new_key argument is 0 it unregisters the existing reservation passed | ||
in old_key. | ||
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2. IOC_PR_RESERVE | ||
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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. | ||
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3. IOC_PR_RELEASE | ||
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This ioctl command releases the reservation specified by key and flags | ||
and thus removes any access restriction implied by it. | ||
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4. IOC_PR_PREEMPT | ||
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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. | ||
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5. IOC_PR_PREEMPT_ABORT | ||
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This ioctl command works like IOC_PR_PREEMPT except that it also aborts | ||
any outstanding command sent over a connection identified by old_key. | ||
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6. IOC_PR_CLEAR | ||
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This ioctl command unregisters both key and any other reservation key | ||
registered with the device and drops any existing reservation. | ||
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Flags | ||
----- | ||
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All the ioctls have a flag field. Currently only one flag is supported: | ||
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- PR_FL_IGNORE_KEY | ||
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Ignore the existing reservation key. This is commonly supported for | ||
IOC_PR_REGISTER, and some implementation may support the flag for | ||
IOC_PR_RESERVE. | ||
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For all unknown flags the kernel will return -EOPNOTSUPP. |
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