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
68 union lower_chunk {
69 union lower_chunk *next;
70 unsigned long data[LOWER_SIZE]; // 2K in size
71 };
72
73 union upper_chunk {
74 union upper_chunk *next;
75 union lower_chunk *data[UPPER2_SIZE]; // 1 or 2K in size
76 };
77
78 struct 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
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