path: root/block/badblocks.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Bad block management
 *
 * - Heavily based on MD badblocks code from Neil Brown
 *
 * Copyright (c) 2015, Intel Corporation.
 */

#include <linux/badblocks.h>
#include <linux/seqlock.h>
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/stddef.h>
#include <linux/types.h>
#include <linux/slab.h>

/*
 * The purpose of badblocks set/clear is to manage bad blocks ranges which are
 * identified by LBA addresses.
 *
 * When the caller of badblocks_set() wants to set a range of bad blocks, the
 * setting range can be acked or unacked. And the setting range may merge,
 * overwrite, skip the overlapped already set range, depends on who they are
 * overlapped or adjacent, and the acknowledgment type of the ranges. It can be
 * more complicated when the setting range covers multiple already set bad block
 * ranges, with restrictions of maximum length of each bad range and the bad
 * table space limitation.
 *
 * It is difficult and unnecessary to take care of all the possible situations,
 * for setting a large range of bad blocks, we can handle it by dividing the
 * large range into smaller ones when encounter overlap, max range length or
 * bad table full conditions. Every time only a smaller piece of the bad range
 * is handled with a limited number of conditions how it is interacted with
 * possible overlapped or adjacent already set bad block ranges. Then the hard
 * complicated problem can be much simpler to handle in proper way.
 *
 * When setting a range of bad blocks to the bad table, the simplified situations
 * to be considered are, (The already set bad blocks ranges are naming with
 *  prefix E, and the setting bad blocks range is naming with prefix S)
 *
 * 1) A setting range is not overlapped or adjacent to any other already set bad
 *    block range.
 *                         +--------+
 *                         |    S   |
 *                         +--------+
 *        +-------------+               +-------------+
 *        |      E1     |               |      E2     |
 *        +-------------+               +-------------+
 *    For this situation if the bad blocks table is not full, just allocate a
 *    free slot from the bad blocks table to mark the setting range S. The
 *    result is,
 *        +-------------+  +--------+   +-------------+
 *        |      E1     |  |    S   |   |      E2     |
 *        +-------------+  +--------+   +-------------+
 * 2) A setting range starts exactly at a start LBA of an already set bad blocks
 *    range.
 * 2.1) The setting range size < already set range size
 *        +--------+
 *        |    S   |
 *        +--------+
 *        +-------------+
 *        |      E      |
 *        +-------------+
 * 2.1.1) If S and E are both acked or unacked range, the setting range S can
 *    be merged into existing bad range E. The result is,
 *        +-------------+
 *        |      S      |
 *        +-------------+
 * 2.1.2) If S is unacked setting and E is acked, the setting will be denied, and
 *    the result is,
 *        +-------------+
 *        |      E      |
 *        +-------------+
 * 2.1.3) If S is acked setting and E is unacked, range S can overwrite on E.
 *    An extra slot from the bad blocks table will be allocated for S, and head
 *    of E will move to end of the inserted range S. The result is,
 *        +--------+----+
 *        |    S   | E  |
 *        +--------+----+
 * 2.2) The setting range size == already set range size
 * 2.2.1) If S and E are both acked or unacked range, the setting range S can
 *    be merged into existing bad range E. The result is,
 *        +-------------+
 *        |      S      |
 *        +-------------+
 * 2.2.2) If S is unacked setting and E is acked, the setting will be denied, and
 *    the result is,
 *        +-------------+
 *        |      E      |
 *        +-------------+
 * 2.2.3) If S is acked setting and E is unacked, range S can overwrite all of
      bad blocks range E. The result is,
 *        +-------------+
 *        |      S      |
 *        +-------------+
 * 2.3) The setting range size > already set range size
 *        +-------------------+
 *        |          S        |
 *        +-------------------+
 *        +-------------+
 *        |      E      |
 *        +-------------+
 *    For such situation, the setting range S can be treated as two parts, the
 *    first part (S1) is as same size as the already set range E, the second
 *    part (S2) is the rest of setting range.
 *        +-------------+-----+        +-------------+       +-----+
 *        |    S1       | S2  |        |     S1      |       | S2  |
 *        +-------------+-----+  ===>  +-------------+       +-----+
 *        +-------------+              +-------------+
 *        |      E      |              |      E      |
 *        +-------------+              +-------------+
 *    Now we only focus on how to handle the setting range S1 and already set
 *    range E, which are already explained in 2.2), for the rest S2 it will be
 *    handled later in next loop.
 * 3) A setting range starts before the start LBA of an already set bad blocks
 *    range.
 *        +-------------+
 *        |      S      |
 *        +-------------+
 *             +-------------+
 *             |      E      |
 *             +-------------+
 *    For this situation, the setting range S can be divided into two parts, the
 *    first (S1) ends at the start LBA of already set range E, the second part
 *    (S2) starts exactly at a start LBA of the already set range E.
 *        +----+---------+             +----+      +---------+
 *        | S1 |    S2   |             | S1 |      |    S2   |
 *        +----+---------+      ===>   +----+      +---------+
 *             +-------------+                     +-------------+
 *             |      E      |                     |      E      |
 *             +-------------+                     +-------------+
 *    Now only the first part S1 should be handled in this loop, which is in
 *    similar condition as 1). The rest part S2 has exact same start LBA address
 *    of the already set range E, they will be handled in next loop in one of
 *    situations in 2).
 * 4) A setting range starts after the start LBA of an already set bad blocks
 *    range.
 * 4.1) If the setting range S exactly matches the tail part of already set bad
 *    blocks range E, like the following chart shows,
 *            +---------+
 *            |   S     |
 *            +---------+
 *        +-------------+
 *        |      E      |
 *        +-------------+
 * 4.1.1) If range S and E have same acknowledge value (b