Documentation/admin-guide/device-mapper/era.rst

Source file repositories/reference/linux-study-clean/Documentation/admin-guide/device-mapper/era.rst

File Facts

System
Linux kernel
Corpus path
Documentation/admin-guide/device-mapper/era.rst
Extension
.rst
Size
3437 bytes
Lines
117
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

======
dm-era
======

Introduction
============

dm-era is a target that behaves similar to the linear target.  In
addition it keeps track of which blocks were written within a user
defined period of time called an 'era'.  Each era target instance
maintains the current era as a monotonically increasing 32-bit
counter.

Use cases include tracking changed blocks for backup software, and
partially invalidating the contents of a cache to restore cache
coherency after rolling back a vendor snapshot.

Constructor
===========

era <metadata dev> <origin dev> <block size>

 ================ ======================================================
 metadata dev     fast device holding the persistent metadata
 origin dev	  device holding data blocks that may change
 block size       block size of origin data device, granularity that is
		  tracked by the target
 ================ ======================================================

Messages
========

None of the dm messages take any arguments.

checkpoint
----------

Possibly move to a new era.  You shouldn't assume the era has
incremented.  After sending this message, you should check the
current era via the status line.

take_metadata_snap
------------------

Create a clone of the metadata, to allow a userland process to read it.

drop_metadata_snap
------------------

Drop the metadata snapshot.

Status
======

<metadata block size> <#used metadata blocks>/<#total metadata blocks>
<current era> <held metadata root | '-'>

========================= ==============================================
metadata block size	  Fixed block size for each metadata block in
			  sectors
#used metadata blocks	  Number of metadata blocks used
#total metadata blocks	  Total number of metadata blocks
current era		  The current era
held metadata root	  The location, in blocks, of the metadata root
			  that has been 'held' for userspace read
			  access. '-' indicates there is no held root
========================= ==============================================

Detailed use case
=================

Annotation

Implementation Notes