linux-imx

/* SPDX-License-Identifier: GPL-2.0 */

/*

 * bitmap.h: Copyright (C) Peter T. Breuer (ptb@ot.uc3m.es) 2003

 *

 * additions: Copyright (C) 2003-2004, Paul Clements, SteelEye Technology, Inc.

 */

#ifndef BITMAP_H

#define BITMAP_H 1

​

#define BITMAP_MAJOR_LO 3

/* version 4 insists the bitmap is in little-endian order

 * with version 3, it is host-endian which is non-portable

 * Version 5 is currently set only for clustered devices

 */

#define BITMAP_MAJOR_HI 4

#define BITMAP_MAJOR_CLUSTERED 5

#define BITMAP_MAJOR_HOSTENDIAN 3

​

/*

 * in-memory bitmap:

 *

 * Use 16 bit block counters to track pending writes to each "chunk".

 * The 2 high order bits are special-purpose, the first is a flag indicating

 * whether a resync is needed.  The second is a flag indicating whether a

 * resync is active.

 * This means that the counter is actually 14 bits:

 *

 * +--------+--------+------------------------------------------------+

 * | resync | resync |               counter                          |

 * | needed | active |                                                |

 * |  (0-1) |  (0-1) |              (0-16383)                         |

 * +--------+--------+------------------------------------------------+

 *

 * The "resync needed" bit is set when:

 *    a '1' bit is read from storage at startup.

 *    a write request fails on some drives

 *    a resync is aborted on a chunk with 'resync active' set

 * It is cleared (and resync-active set) when a resync starts across all drives

 * of the chunk.

 *

 *

 * The "resync active" bit is set when:

 *    a resync is started on all drives, and resync_needed is set.

 *       resync_needed will be cleared (as long as resync_active wasn't already set).

 * It is cleared when a resync completes.

 *

 * The counter counts pending write requests, plus the on-disk bit.

 * When the counter is '1' and the resync bits are clear, the on-disk

 * bit can be cleared as well, thus setting the counter to 0.

 * When we set a bit, or in the counter (to start a write), if the fields is

 * 0, we first set the disk bit and set the counter to 1.

 *

 * If the counter is 0, the on-disk bit is clear and the stripe is clean

 * Anything that dirties the stripe pushes the counter to 2 (at least)

 * and sets the on-disk bit (lazily).

 * If a periodic sweep find the counter at 2, it is decremented to 1.

 * If the sweep find the counter at 1, the on-disk bit is cleared and the

 * counter goes to zero.

 *

 * Also, we'll hijack the "map" pointer itself and use it as two 16 bit block

 * counters as a fallback when "page" memory cannot be allocated:

 *

 * Normal case (page memory allocated):