// 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 … #define UPPER_MAX … #define UPPER1_SIZE … #define UPPER2_SIZE … #define LOWER_BITS … #define LOWER_MAX … #define LOWER_SIZE … #define UPPER1_SHIFT … #define UPPER2_SHIFT … #define LOWER_MASK … #define UPPER_MASK … /* According to linux/thread.h pids can not be bigger than or equal to 1 << 30 */ #define MAX_PID … /* Just keep 6 chunks of both upper and lower in the cache on alloc */ #define CHUNK_ALLOC … /* Have 2 chunks free, trigger a refill of the cache */ #define CHUNK_REALLOC … lower_chunk; upper_chunk; struct trace_pid_list { … }; #endif /* _TRACE_INTERNAL_PID_LIST_H */
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