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// SPDX-License-Identifier: GPL-2.0
/* Do not include this file directly. */
#ifndef _TRACE_INTERNAL_PID_LIST_H
#define _TRACE_INTERNAL_PID_LIST_H
/*
* In order to keep track of what pids to trace, a tree is created much
* like page tables are used. This creates a sparse bit map, where
* the tree is filled in when needed. A PID is at most 30 bits (see
* linux/thread.h), and is broken up into 3 sections based on the bit map
* of the bits. The 8 MSB is the "upper1" section. The next 8 MSB is the
* "upper2" section and the 14 LSB is the "lower" section.
*
* A trace_pid_list structure holds the "upper1" section, in an
* array of 256 pointers (1 or 2K in size) to "upper_chunk" unions, where
* each has an array of 256 pointers (1 or 2K in size) to the "lower_chunk"
* structures, where each has an array of size 2K bytes representing a bitmask
* of the 14 LSB of the PID (256 * 8 = 2048)
*
* When a trace_pid_list is allocated, it includes the 256 pointer array
* of the upper1 unions. Then a "cache" of upper and lower is allocated
* where these will be assigned as needed.
*
* When a bit is set in the pid_list bitmask, the pid to use has
* the 8 MSB masked, and this is used to index the array in the
* pid_list to find the next upper union. If the element is NULL,
* then one is retrieved from the upper_list cache. If none is
* available, then -ENOMEM is returned.
*
* The next 8 MSB is used to index into the "upper2" section. If this
* element is NULL, then it is retrieved from the lower_list cache.
* Again, if one is not available -ENOMEM is returned.
*
* Finally the 14 LSB of the PID is used to set the bit in the 16384
* bitmask (made up of 2K bytes).
*
* When the second upper section or the lower section has their last
* bit cleared, they are added back to the free list to be reused
* when needed.
*/
#define UPPER_BITS 8
#define UPPER_MAX (1 << UPPER_BITS)
#define UPPER1_SIZE (1 << UPPER_BITS)
#define UPPER2_SIZE (1 << UPPER_BITS)
#define LOWER_BITS 14
#define LOWER_MAX (1 << LOWER_BITS)
#define LOWER_SIZE (LOWER_MAX / BITS_PER_LONG)
#define UPPER1_SHIFT (LOWER_BITS + UPPER_BITS)
#define UPPER2_SHIFT LOWER_BITS
#define LOWER_MASK (LOWER_MAX - 1)
#define UPPER_MASK (UPPER_MAX - 1)
/* According to linux/thread.h pids can not be bigger than or equal to 1 << 30 */
#define MAX_PID (1 << 30)
/* Just keep 6 chunks of both upper and lower in the cache on alloc */
#define CHUNK_ALLOC 6
/* Have 2 chunks free, trigger a refill of the cache */
#define CHUNK_REALLOC 2
union lower_chunk {
union lower_chunk *next;
unsigned long data[LOWER_SIZE]; // 2K in size
};
union upper_chunk {
union upper_chunk *next;
union lower_chunk *data[UPPER2_SIZE]; // 1 or 2K in size
};
struct trace_pid_list {
raw_spinlock_t lock;
struct irq_work refill_irqwork;
union upper_chunk *upper[UPPER1_SIZE]; // 1 or 2K in size
union upper_chunk *upper_list;
union lower_chunk *lower_list;
int free_upper_chunks;
int free_lower_chunks;
};
#endif /* _TRACE_INTERNAL_PID_LIST_H */
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