drivers/md/md-bitmap.h

1 /* SPDX-License-Identifier: GPL-2.0 */
5  * additions: Copyright (C) 2003-2004, Paul Clements, SteelEye Technology, Inc.
11 /* version 4 insists the bitmap is in little-endian order
12  * with version 3, it is host-endian which is non-portable
20  * in-memory bitmap:
23  * The 2 high order bits are special-purpose, the first is a flag indicating
26  * This means that the counter is actually 14 bits:
28  * +--------+--------+------------------------------------------------+
29  * | resync | resync |               counter                          |
31  * |  (0-1) |  (0-1) |              (0-16383)                         |
32  * +--------+--------+------------------------------------------------+
38  * It is cleared (and resync-active set) when a resync starts across all drives
47  * The counter counts pending write requests, plus the on-disk bit.
48  * When the counter is '1' and the resync bits are clear, the on-disk
49  * bit can be cleared as well, thus setting the counter to 0.
50  * When we set a bit, or in the counter (to start a write), if the fields is
51  * 0, we first set the disk bit and set the counter to 1.
53  * If the counter is 0, the on-disk bit is clear and the stripe is clean
54  * Anything that dirties the stripe pushes the counter to 2 (at least)
55  * and sets the on-disk bit (lazily).
56  * If a periodic sweep find the counter at 2, it is decremented to 1.
57  * If the sweep find the counter at 1, the on-disk bit is cleared and the
58  * counter goes to zero.
65  *     page pointer (32-bit)
67  *     [ ] ------+
69  *               +-------> [   ][   ]..[   ] (4096 byte page == 2048 counters)
74  *     hijacked page pointer (32-bit)
77  *      counter #1 (16-bit) counter #2 (16-bit)
89 #define COUNTER_BYTE_SHIFT (COUNTER_BIT_SHIFT - 3)
91 #define NEEDED_MASK ((bitmap_counter_t) (1 << (COUNTER_BITS - 1)))
92 #define RESYNC_MASK ((bitmap_counter_t) (1 << (COUNTER_BITS - 2)))
93 #define COUNTER_MAX ((bitmap_counter_t) RESYNC_MASK - 1)
96 #define COUNTER(x) (((bitmap_counter_t) x) & COUNTER_MAX)  macro
101 #define PAGE_COUNTER_SHIFT (PAGE_BIT_SHIFT - COUNTER_BIT_SHIFT)
103 #define PAGE_COUNTER_MASK  (PAGE_COUNTER_RATIO - 1)
115 /* use these for bitmap->flags and bitmap->sb->state bit-fields */
117 	BITMAP_STALE	   = 1,  /* the bitmap file is out of date or had -EIO */
118 	BITMAP_WRITE_ERROR = 2, /* A write error has occurred */
122 /* the superblock at the front of the bitmap file -- little endian */
126 	__u8  uuid[16];      /*  8  128 bit uuid - must match md device uuid */
127 	__le64 events;       /* 24  event counter for the bitmap (1)*/
128 	__le64 events_cleared;/*32  event counter when last bit cleared (2) */
133 	__le32 write_behind; /* 60  number of outstanding write-behind writes */
134 	__le32 sectors_reserved; /* 64 number of 512-byte sectors that are
138 	__u8  pad[256 - 136]; /* set to zero */
142  * (1) This event counter is updated before the eventcounter in the md superblock
143  *    When a bitmap is loaded, it is only accepted if this event counter is equal
144  *    to, or one greater than, the event counter in the superblock.
145  * (2) This event counter is updated when the other one is *if*and*only*if* the
157 /* the in-memory bitmap is represented by bitmap_pages */
169 	 * If any counter in this page is '1' or '2' - and so could be
179 /* the main bitmap structure - one per mddev */
189 		unsigned long chunkshift;	/* chunksize = 2^chunkshift
221 	 * the bitmap daemon - periodically wakes up and sweeps the bitmap
281 	return bitmap && bitmap->storage.filemap &&  in md_bitmap_enabled()
282 	       !test_bit(BITMAP_STALE, &bitmap->flags);  in md_bitmap_enabled()