comm.c

  1// SPDX-License-Identifier: GPL-2.0
  2#include "comm.h"
  3#include <errno.h>
  4#include <string.h>
  5#include <internal/rc_check.h>
  6#include <linux/refcount.h>
  7#include <linux/zalloc.h>
  8#include <tools/libc_compat.h> // reallocarray
  9
 10#include "rwsem.h"
 11
 12DECLARE_RC_STRUCT(comm_str) {
 13	refcount_t refcnt;
 14	char str[];
 15};
 16
 17static struct comm_strs {
 18	struct rw_semaphore lock;
 19	struct comm_str **strs;
 20	int num_strs;
 21	int capacity;
 22} _comm_strs;
 23
 24static void comm_strs__remove_if_last(struct comm_str *cs);
 25
 26static void comm_strs__init(void)
 27	NO_THREAD_SAFETY_ANALYSIS /* Inherently single threaded due to pthread_once. */
 28{
 29	init_rwsem(&_comm_strs.lock);
 30	_comm_strs.capacity = 16;
 31	_comm_strs.num_strs = 0;
 32	_comm_strs.strs = calloc(16, sizeof(*_comm_strs.strs));
 33}
 34
 35static struct comm_strs *comm_strs__get(void)
 36{
 37	static pthread_once_t comm_strs_type_once = PTHREAD_ONCE_INIT;
 38
 39	pthread_once(&comm_strs_type_once, comm_strs__init);
 40
 41	return &_comm_strs;
 42}
 43
 44static refcount_t *comm_str__refcnt(struct comm_str *cs)
 45{
 46	return &RC_CHK_ACCESS(cs)->refcnt;
 47}
 48
 49static const char *comm_str__str(const struct comm_str *cs)
 50{
 51	return &RC_CHK_ACCESS(cs)->str[0];
 52}
 53
 54static struct comm_str *comm_str__get(struct comm_str *cs)
 55{
 56	struct comm_str *result;
 57
 58	if (RC_CHK_GET(result, cs))
 59		refcount_inc_not_zero(comm_str__refcnt(cs));
 60
 61	return result;
 62}
 63
 64static void comm_str__put(struct comm_str *cs)
 65{
 66	if (!cs)
 67		return;
 68
 69	if (refcount_dec_and_test(comm_str__refcnt(cs))) {
 70		RC_CHK_FREE(cs);
 71	} else {
 72		if (refcount_read(comm_str__refcnt(cs)) == 1)
 73			comm_strs__remove_if_last(cs);
 74
 75		RC_CHK_PUT(cs);
 76	}
 77}
 78
 79static struct comm_str *comm_str__new(const char *str)
 80{
 81	struct comm_str *result = NULL;
 82	RC_STRUCT(comm_str) *cs;
 83
 84	cs = malloc(sizeof(*cs) + strlen(str) + 1);
 85	if (ADD_RC_CHK(result, cs)) {
 86		refcount_set(comm_str__refcnt(result), 1);
 87		strcpy(&cs->str[0], str);
 88	}
 89	return result;
 90}
 91
 92static int comm_str__search(const void *_key, const void *_member)
 93{
 94	const char *key = _key;
 95	const struct comm_str *member = *(const struct comm_str * const *)_member;
 96
 97	return strcmp(key, comm_str__str(member));
 98}
 99
100static void comm_strs__remove_if_last(struct comm_str *cs)
101{
102	struct comm_strs *comm_strs = comm_strs__get();
103
104	down_write(&comm_strs->lock);
105	/*
106	 * Are there only references from the array, if so remove the array
107	 * reference under the write lock so that we don't race with findnew.
108	 */
109	if (refcount_read(comm_str__refcnt(cs)) == 1) {
110		struct comm_str **entry;
111
112		entry = bsearch(comm_str__str(cs), comm_strs->strs, comm_strs->num_strs,
113				sizeof(struct comm_str *), comm_str__search);
114		comm_str__put(*entry);
115		for (int i = entry - comm_strs->strs; i < comm_strs->num_strs - 1; i++)
116			comm_strs->strs[i] = comm_strs->strs[i + 1];
117		comm_strs->num_strs--;
118	}
119	up_write(&comm_strs->lock);
120}
121
122static struct comm_str *__comm_strs__find(struct comm_strs *comm_strs, const char *str)
123	SHARED_LOCKS_REQUIRED(comm_strs->lock)
124{
125	struct comm_str **result;
126
127	result = bsearch(str, comm_strs->strs, comm_strs->num_strs, sizeof(struct comm_str *),
128			 comm_str__search);
129
130	if (!result)
131		return NULL;
132
133	return comm_str__get(*result);
134}
135
136static struct comm_str *comm_strs__findnew(const char *str)
137{
138	struct comm_strs *comm_strs = comm_strs__get();
139	struct comm_str *result;
140
141	if (!comm_strs)
142		return NULL;
143
144	down_read(&comm_strs->lock);
145	result = __comm_strs__find(comm_strs, str);
146	up_read(&comm_strs->lock);
147	if (result)
148		return result;
149
150	down_write(&comm_strs->lock);
151	result = __comm_strs__find(comm_strs, str);
152	if (!result) {
153		if (comm_strs->num_strs == comm_strs->capacity) {
154			struct comm_str **tmp;
155
156			tmp = reallocarray(comm_strs->strs,
157					   comm_strs->capacity + 16,
158					   sizeof(*comm_strs->strs));
159			if (!tmp) {
160				up_write(&comm_strs->lock);
161				return NULL;
162			}
163			comm_strs->strs = tmp;
164			comm_strs->capacity += 16;
165		}
166		result = comm_str__new(str);
167		if (result) {
168			int low = 0, high = comm_strs->num_strs - 1;
169			int insert = comm_strs->num_strs; /* Default to inserting at the end. */
170
171			while (low <= high) {
172				int mid = low + (high - low) / 2;
173				int cmp = strcmp(comm_str__str(comm_strs->strs[mid]), str);
174
175				if (cmp < 0) {
176					low = mid + 1;
177				} else {
178					high = mid - 1;
179					insert = mid;
180				}
181			}
182			memmove(&comm_strs->strs[insert + 1], &comm_strs->strs[insert],
183				(comm_strs->num_strs - insert) * sizeof(struct comm_str *));
184			comm_strs->num_strs++;
185			comm_strs->strs[insert] = result;
186		}
187	}
188	up_write(&comm_strs->lock);
189	return comm_str__get(result);
190}
191
192struct comm *comm__new(const char *str, u64 timestamp, bool exec)
193{
194	struct comm *comm = zalloc(sizeof(*comm));
195
196	if (!comm)
197		return NULL;
198
199	comm->start = timestamp;
200	comm->exec = exec;
201
202	comm->comm_str = comm_strs__findnew(str);
203	if (!comm->comm_str) {
204		free(comm);
205		return NULL;
206	}
207
208	return comm;
209}
210
211int comm__override(struct comm *comm, const char *str, u64 timestamp, bool exec)
212{
213	struct comm_str *new, *old = comm->comm_str;
214
215	new = comm_strs__findnew(str);
216	if (!new)
217		return -ENOMEM;
218
219	comm_str__put(old);
220	comm->comm_str = new;
221	comm->start = timestamp;
222	if (exec)
223		comm->exec = true;
224
225	return 0;
226}
227
228void comm__free(struct comm *comm)
229{
230	comm_str__put(comm->comm_str);
231	free(comm);
232}
233
234const char *comm__str(const struct comm *comm)
235{
236	return comm_str__str(comm->comm_str);
237}