1// SPDX-License-Identifier: GPL-2.0
2
3/* Do not include this file directly. */
4
5#ifndef _TRACE_INTERNAL_PID_LIST_H
6#define _TRACE_INTERNAL_PID_LIST_H
7
8/*
9 * In order to keep track of what pids to trace, a tree is created much
10 * like page tables are used. This creates a sparse bit map, where
11 * the tree is filled in when needed. A PID is at most 30 bits (see
12 * linux/thread.h), and is broken up into 3 sections based on the bit map
13 * of the bits. The 8 MSB is the "upper1" section. The next 8 MSB is the
14 * "upper2" section and the 14 LSB is the "lower" section.
15 *
16 * A trace_pid_list structure holds the "upper1" section, in an
17 * array of 256 pointers (1 or 2K in size) to "upper_chunk" unions, where
18 * each has an array of 256 pointers (1 or 2K in size) to the "lower_chunk"
19 * structures, where each has an array of size 2K bytes representing a bitmask
20 * of the 14 LSB of the PID (256 * 8 = 2048)
21 *
22 * When a trace_pid_list is allocated, it includes the 256 pointer array
23 * of the upper1 unions. Then a "cache" of upper and lower is allocated
24 * where these will be assigned as needed.
25 *
26 * When a bit is set in the pid_list bitmask, the pid to use has
27 * the 8 MSB masked, and this is used to index the array in the
28 * pid_list to find the next upper union. If the element is NULL,
29 * then one is retrieved from the upper_list cache. If none is
30 * available, then -ENOMEM is returned.
31 *
32 * The next 8 MSB is used to index into the "upper2" section. If this
33 * element is NULL, then it is retrieved from the lower_list cache.
34 * Again, if one is not available -ENOMEM is returned.
35 *
36 * Finally the 14 LSB of the PID is used to set the bit in the 16384
37 * bitmask (made up of 2K bytes).
38 *
39 * When the second upper section or the lower section has their last
40 * bit cleared, they are added back to the free list to be reused
41 * when needed.
42 */
43
44#define UPPER_BITS	8
45#define UPPER_MAX	(1 << UPPER_BITS)
46#define UPPER1_SIZE	(1 << UPPER_BITS)
47#define UPPER2_SIZE	(1 << UPPER_BITS)
48
49#define LOWER_BITS	14
50#define LOWER_MAX	(1 << LOWER_BITS)
51#define LOWER_SIZE	(LOWER_MAX / BITS_PER_LONG)
52
53#define UPPER1_SHIFT	(LOWER_BITS + UPPER_BITS)
54#define UPPER2_SHIFT	LOWER_BITS
55#define LOWER_MASK	(LOWER_MAX - 1)
56
57#define UPPER_MASK	(UPPER_MAX - 1)
58
59/* According to linux/thread.h pids can not be bigger than or equal to 1 << 30 */
60#define MAX_PID		(1 << 30)
61
62/* Just keep 6 chunks of both upper and lower in the cache on alloc */
63#define CHUNK_ALLOC 6
64
65/* Have 2 chunks free, trigger a refill of the cache */
66#define CHUNK_REALLOC 2
67
68union lower_chunk {
69	union lower_chunk		*next;
70	unsigned long			data[LOWER_SIZE]; // 2K in size
71};
72
73union upper_chunk {
74	union upper_chunk		*next;
75	union lower_chunk		*data[UPPER2_SIZE]; // 1 or 2K in size
76};
77
78struct trace_pid_list {
79	raw_spinlock_t			lock;
80	struct irq_work			refill_irqwork;
81	union upper_chunk		*upper[UPPER1_SIZE]; // 1 or 2K in size
82	union upper_chunk		*upper_list;
83	union lower_chunk		*lower_list;
84	int				free_upper_chunks;
85	int				free_lower_chunks;
86};
87
88#endif /* _TRACE_INTERNAL_PID_LIST_H */
89