1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
|
/* Helper code for POSIX semaphore implementation.
Copyright (C) 2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <search.h>
#include <semaphoreP.h>
#include <sys/mman.h>
#include <sem_routines.h>
/* Keeping track of currently used mappings. */
struct inuse_sem
{
dev_t dev;
ino_t ino;
int refcnt;
sem_t *sem;
char name[];
};
/* Comparison function for search of existing mapping. */
static int
sem_search (const void *a, const void *b)
{
const struct inuse_sem *as = (const struct inuse_sem *) a;
const struct inuse_sem *bs = (const struct inuse_sem *) b;
if (as->ino != bs->ino)
/* Cannot return the difference the type is larger than int. */
return as->ino < bs->ino ? -1 : (as->ino == bs->ino ? 0 : 1);
if (as->dev != bs->dev)
/* Cannot return the difference the type is larger than int. */
return as->dev < bs->dev ? -1 : (as->dev == bs->dev ? 0 : 1);
return strcmp (as->name, bs->name);
}
/* The search tree for existing mappings. */
static void *sem_mappings;
/* Lock to protect the search tree. */
static int sem_mappings_lock = LLL_LOCK_INITIALIZER;
/* Search for existing mapping and if possible add the one provided. */
sem_t *
__sem_check_add_mapping (const char *name, int fd, sem_t *existing)
{
size_t namelen = strlen (name);
sem_t *result = SEM_FAILED;
/* Get the information about the file. */
struct stat64 st;
if (__fstat64 (fd, &st) == 0)
{
/* Get the lock. */
lll_lock (sem_mappings_lock, LLL_PRIVATE);
/* Search for an existing mapping given the information we have. */
struct inuse_sem *fake;
fake = (struct inuse_sem *) alloca (sizeof (*fake) + namelen);
memcpy (fake->name, name, namelen);
fake->dev = st.st_dev;
fake->ino = st.st_ino;
struct inuse_sem **foundp = __tfind (fake, &sem_mappings, sem_search);
if (foundp != NULL)
{
/* There is already a mapping. Use it. */
result = (*foundp)->sem;
++(*foundp)->refcnt;
}
else
{
/* We haven't found a mapping. Install ione. */
struct inuse_sem *newp;
newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen);
if (newp != NULL)
{
/* If the caller hasn't provided any map it now. */
if (existing == SEM_FAILED)
existing = (sem_t *) mmap (NULL, sizeof (sem_t),
PROT_READ | PROT_WRITE, MAP_SHARED,
fd, 0);
newp->dev = st.st_dev;
newp->ino = st.st_ino;
newp->refcnt = 1;
newp->sem = existing;
memcpy (newp->name, name, namelen);
/* Insert the new value. */
if (existing != MAP_FAILED
&& __tsearch (newp, &sem_mappings, sem_search) != NULL)
/* Successful. */
result = existing;
else
/* Something went wrong while inserting the new
value. We fail completely. */
free (newp);
}
}
/* Release the lock. */
lll_unlock (sem_mappings_lock, LLL_PRIVATE);
}
if (result != existing && existing != SEM_FAILED && existing != MAP_FAILED)
{
/* Do not disturb errno. */
int save = errno;
munmap (existing, sizeof (sem_t));
errno = save;
}
return result;
}
struct walk_closure
{
sem_t *the_sem;
struct inuse_sem *rec;
};
static void
walker (const void *inodep, VISIT which, void *closure0)
{
struct walk_closure *closure = closure0;
struct inuse_sem *nodep = *(struct inuse_sem **) inodep;
if (nodep->sem == closure->the_sem)
closure->rec = nodep;
}
bool
__sem_remove_mapping (sem_t *sem)
{
bool ret = true;
/* Get the lock. */
lll_lock (sem_mappings_lock, LLL_PRIVATE);
/* Locate the entry for the mapping the caller provided. */
struct inuse_sem *rec;
{
struct walk_closure closure = { .the_sem = sem, .rec = NULL };
__twalk_r (sem_mappings, walker, &closure);
rec = closure.rec;
}
if (rec != NULL)
{
/* Check the reference counter. If it is going to be zero, free
all the resources. */
if (--rec->refcnt == 0)
{
/* Remove the record from the tree. */
__tdelete (rec, &sem_mappings, sem_search);
if (munmap (rec->sem, sizeof (sem_t)) == -1)
ret = false;
free (rec);
}
}
else
ret = false;
/* Release the lock. */
lll_unlock (sem_mappings_lock, LLL_PRIVATE);
return ret;
}
|
