linux-imx

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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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