aboutsummaryrefslogtreecommitdiff
path: root/nptl/sem_open.c
blob: 6fc72f7dc6be5cfe3ab7e8f4c1a50ff1d5d0799a (plain)
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
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
/* Copyright (C) 2002 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.

   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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <errno.h>
#include <fcntl.h>
#include <mntent.h>
#include <paths.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/statfs.h>
#include <linux_fsinfo.h>
#include "semaphoreP.h"



/* Information about the mount point.  */
struct mountpoint_info mountpoint attribute_hidden;

/* This is the default mount point.  */
static const char defaultmount[] = "/dev/shm";
/* This is the default directory.  */
static const char defaultdir[] = "/dev/shm/sem.";

/* Protect the `mountpoint' variable above.  */
pthread_once_t __namedsem_once attribute_hidden = PTHREAD_ONCE_INIT;


/* Determine where the shmfs is mounted (if at all).  */
void
attribute_hidden
__where_is_shmfs (void)
{
  char buf[512];
  struct statfs f;
  struct mntent resmem;
  struct mntent *mp;
  FILE *fp;

  /* The canonical place is /dev/shm.  This is at least what the
     documentation tells everybody to do.  */
  if (__statfs (defaultmount, &f) == 0 && f.f_type == SHMFS_SUPER_MAGIC)
    {
      /* It is in the normal place.  */
      mountpoint.dir = (char *) defaultdir;
      mountpoint.dirlen = sizeof (defaultdir) - 1;

      return;
    }

  /* OK, do it the hard way.  Look through the /proc/mounts file and if
     this does not exist through /etc/fstab to find the mount point.  */
  fp = __setmntent ("/proc/mounts", "r");
  if (__builtin_expect (fp == NULL, 0))
    {
      fp = __setmntent (_PATH_MNTTAB, "r");
      if (__builtin_expect (fp == NULL, 0))
	/* There is nothing we can do.  Blind guesses are not helpful.  */
	return;
    }

  /* Now read the entries.  */
  while ((mp = __getmntent_r (fp, &resmem, buf, sizeof buf)) != NULL)
    /* The original name is "shm" but this got changed in early Linux
       2.4.x to "tmpfs".  */
    if (strcmp (mp->mnt_type, "tmpfs") == 0
	|| strcmp (mp->mnt_type, "shm") == 0)
      {
	/* Found it.  There might be more than one place where the
           filesystem is mounted but one is enough for us.  */
	size_t namelen;

	/* First make sure this really is the correct entry.  At least
	   some versions of the kernel give wrong information because
	   of the implicit mount of the shmfs for SysV IPC.  */
	if (__statfs (mp->mnt_dir, &f) != 0 || f.f_type != SHMFS_SUPER_MAGIC)
	  continue;

	namelen = strlen (mp->mnt_dir);

	if (namelen == 0)
	  /* Hum, maybe some crippled entry.  Keep on searching.  */
	  continue;

	mountpoint.dir = (char *) malloc (namelen + 4 + 2);
	if (mountpoint.dir != NULL)
	  {
	    char *cp = __mempcpy (mountpoint.dir, mp->mnt_dir, namelen);
	    if (cp[-1] != '/')
	      *cp++ = '/';
	    cp = stpcpy (cp, "sem.");
	    mountpoint.dirlen = cp - mountpoint.dir;
	  }

	break;
      }

  /* Close the stream.  */
  __endmntent (fp);
}


sem_t *
sem_open (const char *name, int oflag, ...)
{
  char *finalname;
  size_t namelen;
  sem_t *result;
  int fd;

  /* Determine where the shmfs is mounted.  */
  pthread_once (&__namedsem_once, __where_is_shmfs);

  /* If we don't know the mount points there is nothing we can do.  Ever.  */
  if (mountpoint.dir == NULL)
    {
      __set_errno (ENOSYS);
      return SEM_FAILED;
    }

  /* Construct the filename.  */
  while (name[0] == '/')
    ++name;

  if (name[0] == '\0')
    {
      /* The name "/" is not supported.  */
      __set_errno (EINVAL);
      return SEM_FAILED;
    }
  namelen = strlen (name);

  /* Create the name of the final file.  */
  finalname = (char *) alloca (mountpoint.dirlen + namelen + 1);
  __mempcpy (__mempcpy (finalname, mountpoint.dir, mountpoint.dirlen),
	     name, namelen + 1);

  /* If the semaphore object has to exist simply open it.  */
  if ((oflag & O_CREAT) == 0)
    {
      fd = open (finalname, oflag | O_NOFOLLOW);

      if (fd == -1)
	/* Return.  errno is already set.  */
	return SEM_FAILED;

      /* Map the sem_t structure from the file.  */
      result = (sem_t *) mmap (NULL, sizeof (sem_t), PROT_READ | PROT_WRITE,
			       MAP_SHARED, fd, 0);
    }
  else
    {
      /* We have to open a temporary file first since it must have the
	 correct form before we can start using it.  */
      char *tmpfname;
      mode_t mode;
      unsigned int value;
      va_list ap;

      va_start (ap, oflag);

      mode = va_arg (ap, mode_t);
      value = va_arg (ap, unsigned int);

      va_end (ap);

      if (value > SEM_VALUE_MAX)
	{
	  __set_errno (EINVAL);
	  return SEM_FAILED;
	}

      tmpfname = (char *) alloca (mountpoint.dirlen + 6 + 1);
      strcpy (__mempcpy (tmpfname, mountpoint.dir, mountpoint.dirlen),
	      "XXXXXX");

      fd = mkstemp (tmpfname);
      if (fd == -1)
	return SEM_FAILED;

      /* Create the initial file content.  */
      sem_t initsem;

      struct sem *iinitsem = (struct sem *) &initsem;
      iinitsem->count = value;

      /* Initialize the remaining bytes as well.  */
      memset ((char *) &initsem + sizeof (struct sem), '\0',
	      sizeof (sem_t) - sizeof (struct sem));

      if (TEMP_FAILURE_RETRY (write (fd, &initsem, sizeof (sem_t)))
	  != sizeof (sem_t)
	  /* Adjust the permission.  */
	  || fchmod (fd, mode) != 0)
	{
	unlink_return:
	  unlink (tmpfname);
	  return SEM_FAILED;
	}

      /* Map the sem_t structure from the file.  */
      result = (sem_t *) mmap (NULL, sizeof (sem_t), PROT_READ | PROT_WRITE,
			       MAP_SHARED, fd, 0);
      if (result == MAP_FAILED)
	goto unlink_return;

      /* Create or overwrite the file.  Depending on what is wanted we
	 use rename or link.  */
      if ((oflag & O_EXCL) == 0)
	{
	  /* An existing file gets overwritten.  */
	  if (rename (tmpfname, finalname) != 0)
	    {
	    unmap_unlink_return:
	      munmap (result, sizeof (sem_t));
	      goto unlink_return;
	    }
	}
      else
	{
	  /* Don't overwrite an existing file.  */
	  if (link (tmpfname, finalname) != 0)
	    goto unmap_unlink_return;

	  /* This went well.  Now remove the temporary name.  This
	     should never fail.  If it fails we leak a file name.
	     Better fix the kernel.  */
	  (void) unlink (tmpfname);
	}
    }

  /* We don't need the file descriptor anymore.  */
  close (fd);

  return result;
}