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da4aea0b | 1 | /* Helper code for POSIX semaphore implementation. |
dff8da6b | 2 | Copyright (C) 2021-2024 Free Software Foundation, Inc. |
da4aea0b AZ |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
17 | <https://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #include <search.h> | |
20 | #include <semaphoreP.h> | |
21 | #include <sys/mman.h> | |
22 | #include <sem_routines.h> | |
23 | ||
24 | /* Keeping track of currently used mappings. */ | |
25 | struct inuse_sem | |
26 | { | |
27 | dev_t dev; | |
894755e1 | 28 | ino64_t ino; |
da4aea0b AZ |
29 | int refcnt; |
30 | sem_t *sem; | |
31 | char name[]; | |
32 | }; | |
33 | ||
c1f46f9d AZ |
34 | struct search_sem |
35 | { | |
36 | dev_t dev; | |
894755e1 | 37 | ino64_t ino; |
c1f46f9d AZ |
38 | int refcnt; |
39 | sem_t *sem; | |
7dd41649 | 40 | char name[NAME_MAX + 1]; |
c1f46f9d AZ |
41 | }; |
42 | ||
da4aea0b AZ |
43 | /* Comparison function for search of existing mapping. */ |
44 | static int | |
45 | sem_search (const void *a, const void *b) | |
46 | { | |
47 | const struct inuse_sem *as = (const struct inuse_sem *) a; | |
48 | const struct inuse_sem *bs = (const struct inuse_sem *) b; | |
49 | ||
50 | if (as->ino != bs->ino) | |
51 | /* Cannot return the difference the type is larger than int. */ | |
52 | return as->ino < bs->ino ? -1 : (as->ino == bs->ino ? 0 : 1); | |
53 | ||
54 | if (as->dev != bs->dev) | |
55 | /* Cannot return the difference the type is larger than int. */ | |
56 | return as->dev < bs->dev ? -1 : (as->dev == bs->dev ? 0 : 1); | |
57 | ||
58 | return strcmp (as->name, bs->name); | |
59 | } | |
60 | ||
61 | /* The search tree for existing mappings. */ | |
62 | static void *sem_mappings; | |
63 | ||
64 | /* Lock to protect the search tree. */ | |
65 | static int sem_mappings_lock = LLL_LOCK_INITIALIZER; | |
66 | ||
67 | ||
68 | /* Search for existing mapping and if possible add the one provided. */ | |
69 | sem_t * | |
70 | __sem_check_add_mapping (const char *name, int fd, sem_t *existing) | |
71 | { | |
72 | size_t namelen = strlen (name); | |
c1f46f9d AZ |
73 | if (namelen > NAME_MAX) |
74 | return SEM_FAILED; | |
e9915681 | 75 | namelen += 1; |
c1f46f9d | 76 | |
da4aea0b AZ |
77 | sem_t *result = SEM_FAILED; |
78 | ||
79 | /* Get the information about the file. */ | |
894755e1 AZ |
80 | struct __stat64_t64 st; |
81 | if (__fstat64_time64 (fd, &st) == 0) | |
da4aea0b AZ |
82 | { |
83 | /* Get the lock. */ | |
84 | lll_lock (sem_mappings_lock, LLL_PRIVATE); | |
85 | ||
86 | /* Search for an existing mapping given the information we have. */ | |
c1f46f9d AZ |
87 | struct search_sem fake; |
88 | memcpy (fake.name, name, namelen); | |
89 | fake.dev = st.st_dev; | |
90 | fake.ino = st.st_ino; | |
da4aea0b | 91 | |
c1f46f9d | 92 | struct inuse_sem **foundp = __tfind (&fake, &sem_mappings, sem_search); |
da4aea0b AZ |
93 | if (foundp != NULL) |
94 | { | |
95 | /* There is already a mapping. Use it. */ | |
96 | result = (*foundp)->sem; | |
97 | ++(*foundp)->refcnt; | |
98 | } | |
99 | else | |
100 | { | |
101 | /* We haven't found a mapping. Install ione. */ | |
102 | struct inuse_sem *newp; | |
103 | ||
104 | newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen); | |
105 | if (newp != NULL) | |
106 | { | |
107 | /* If the caller hasn't provided any map it now. */ | |
108 | if (existing == SEM_FAILED) | |
0b7d48d1 FW |
109 | existing = (sem_t *) __mmap (NULL, sizeof (sem_t), |
110 | PROT_READ | PROT_WRITE, | |
111 | MAP_SHARED, fd, 0); | |
da4aea0b AZ |
112 | |
113 | newp->dev = st.st_dev; | |
114 | newp->ino = st.st_ino; | |
115 | newp->refcnt = 1; | |
116 | newp->sem = existing; | |
117 | memcpy (newp->name, name, namelen); | |
118 | ||
119 | /* Insert the new value. */ | |
120 | if (existing != MAP_FAILED | |
121 | && __tsearch (newp, &sem_mappings, sem_search) != NULL) | |
122 | /* Successful. */ | |
123 | result = existing; | |
124 | else | |
125 | /* Something went wrong while inserting the new | |
126 | value. We fail completely. */ | |
127 | free (newp); | |
128 | } | |
129 | } | |
130 | ||
131 | /* Release the lock. */ | |
132 | lll_unlock (sem_mappings_lock, LLL_PRIVATE); | |
133 | } | |
134 | ||
135 | if (result != existing && existing != SEM_FAILED && existing != MAP_FAILED) | |
136 | { | |
137 | /* Do not disturb errno. */ | |
138 | int save = errno; | |
0b7d48d1 | 139 | __munmap (existing, sizeof (sem_t)); |
da4aea0b AZ |
140 | errno = save; |
141 | } | |
142 | ||
143 | return result; | |
144 | } | |
145 | ||
146 | struct walk_closure | |
147 | { | |
148 | sem_t *the_sem; | |
149 | struct inuse_sem *rec; | |
150 | }; | |
151 | ||
152 | static void | |
153 | walker (const void *inodep, VISIT which, void *closure0) | |
154 | { | |
155 | struct walk_closure *closure = closure0; | |
156 | struct inuse_sem *nodep = *(struct inuse_sem **) inodep; | |
157 | ||
158 | if (nodep->sem == closure->the_sem) | |
159 | closure->rec = nodep; | |
160 | } | |
161 | ||
162 | bool | |
163 | __sem_remove_mapping (sem_t *sem) | |
164 | { | |
165 | bool ret = true; | |
166 | ||
167 | /* Get the lock. */ | |
168 | lll_lock (sem_mappings_lock, LLL_PRIVATE); | |
169 | ||
170 | /* Locate the entry for the mapping the caller provided. */ | |
171 | struct inuse_sem *rec; | |
172 | { | |
173 | struct walk_closure closure = { .the_sem = sem, .rec = NULL }; | |
174 | __twalk_r (sem_mappings, walker, &closure); | |
175 | rec = closure.rec; | |
176 | } | |
177 | if (rec != NULL) | |
178 | { | |
179 | /* Check the reference counter. If it is going to be zero, free | |
180 | all the resources. */ | |
181 | if (--rec->refcnt == 0) | |
182 | { | |
183 | /* Remove the record from the tree. */ | |
184 | __tdelete (rec, &sem_mappings, sem_search); | |
185 | ||
0b7d48d1 | 186 | if (__munmap (rec->sem, sizeof (sem_t)) == -1) |
da4aea0b AZ |
187 | ret = false; |
188 | ||
189 | free (rec); | |
190 | } | |
191 | } | |
192 | else | |
193 | ret = false; | |
194 | ||
195 | /* Release the lock. */ | |
196 | lll_unlock (sem_mappings_lock, LLL_PRIVATE); | |
197 | ||
198 | return ret; | |
199 | } |