Package: glibc / 2.28-10

hurd-i386/tg-sysvshm.diff Patch series | download
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
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
From: Marcus Brinkmann <marcus@gnu.org>
Subject: [PATCH] Implement SysV shared memory for GNU/Hurd.

2005-07-11  Marcus Brinkmann  <marcus@gnu.org>

        * hurd/Makefile (routines): Add sysvshm.
        (distribute): Add sysvshm.h.
        * hurd/sysvshm.h: New file.
        * hurd/sysvshm.c: New file.
        * sysdeps/mach/hurd/bits/stat.h (S_IMMAP0): New macro.
        (S_ISPARE): Unset the S_IMMAP0 flag.
        * sysdeps/mach/hurd/ftok.c: New file.
        * sysdeps/mach/hurd/shmat.c: New file.
        * sysdeps/mach/hurd/shmctl.c: New file.
        * sysdeps/mach/hurd/shmdt.c: New file.
        * sysdeps/mach/hurd/bits/posix_opt.h: Define _XOPEN_SHM to 1.

TODO:
> +  char filename[sizeof (SHM_DIR) - 1 + SHM_NAMEMAX];
> +  struct stat statbuf;
> +
> +  sprintf (filename, SHM_DIR SHM_NAMEPRI, id);
> +  /* SysV requires read access for IPC_STAT.  */
> +  fd = __open (filename, O_NORW);
> +  if (fd < 0)
> +    {
> +      if (errno == ENOENT)
> +     errno = EINVAL;
> +      return -1;
> +    }

Since this is repeated in more than one function, put it into an
internal subroutine.  Then we have only one place doing the
name-generation logic.

> +    case IPC_RMID:
> +      res = __unlink (filename);
> +      /* FIXME: Check error (mapping ENOENT to EINVAL).  */

Fix it.

---
 hurd/Makefile                      |    1 
 hurd/sysvshm.c                     |   97 ++++++++++++++
 hurd/sysvshm.h                     |   47 +++++++
 sysdeps/mach/hurd/bits/posix_opt.h |    4 
 sysdeps/mach/hurd/ftok.c           |   43 ++++++
 sysdeps/mach/hurd/shmat.c          |   79 ++++++++++++
 sysdeps/mach/hurd/shmctl.c         |  132 ++++++++++++++++++++
 sysdeps/mach/hurd/shmdt.c          |   51 +++++++
 sysdeps/mach/hurd/shmget.c         |  242 +++++++++++++++++++++++++++++++++++++
 9 files changed, 694 insertions(+), 2 deletions(-)

--- a/hurd/Makefile
+++ b/hurd/Makefile
@@ -55,6 +55,7 @@
 	   ports-get ports-set hurdports hurdmsg \
 	   errno-loc \
 	   hurdlock \
+	   sysvshm \
 	   $(sig) $(dtable) $(inlines) port-cleanup report-wait xattr
 sig	= hurdsig hurdfault siginfo hurd-raise preempt-sig \
 	  trampoline longjmp-ts catch-exc exc2signal hurdkill sigunwind \
--- /dev/null
+++ b/hurd/sysvshm.c
@@ -0,0 +1,97 @@
+/* Copyright (C) 2005 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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stddef.h>
+#include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <sys/stat.h>
+#include <sys/shm.h>
+
+
+/* Description of an shm attachment.  */
+struct sysvshm_attach
+{
+  /* Linked list.  */
+  struct sysvshm_attach *next;
+
+  /* Map address.  */
+  void *addr;
+
+  /* Map size.  */
+  size_t size;
+};
+
+/* List of attachments.  */
+static struct sysvshm_attach *attach_list;
+
+/* A lock to protect the linked list of shared memory attachments.  */
+static unsigned int sysvshm_lock = LLL_INITIALIZER;
+
+
+/* Adds a segment attachment.  */
+error_t
+__sysvshm_add (void *addr, size_t size)
+{
+  struct sysvshm_attach *shm;
+
+  shm = malloc (sizeof (*shm));
+  if (!shm)
+    return errno;
+
+  __mutex_lock (&sysvshm_lock);
+  shm->addr = addr;
+  shm->size = size;
+  shm->next = attach_list;
+  attach_list = shm;
+  __mutex_unlock (&sysvshm_lock);
+
+  return 0;
+}
+
+/* Removes a segment attachment.  Returns its size if found, or EINVAL
+   otherwise.  */
+error_t
+__sysvshm_remove (void *addr, size_t *size)
+{
+  struct sysvshm_attach *shm;
+  struct sysvshm_attach **pshm = &attach_list;
+
+  __mutex_lock (&sysvshm_lock);
+  shm = attach_list;
+  while (shm)
+    {
+      shm = *pshm;
+      if (shm->addr == addr)
+	{
+	  *pshm = shm->next;
+	  *size = shm->size;
+	  __mutex_unlock (&sysvshm_lock);
+	  free (shm);
+	  return 0;
+	}
+      pshm = &shm->next;
+      shm = shm->next;
+    }
+  __mutex_unlock (&sysvshm_lock);
+  return EINVAL;
+}
--- /dev/null
+++ b/hurd/sysvshm.h
@@ -0,0 +1,47 @@
+/* Copyright (C) 2005 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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <paths.h>
+#include <hurd.h>
+
+/* The area (from top to bottom) that is used for private keys.  These
+   are all keys that have the second highest bit set.  */
+#define SHM_PRIV_KEY_START INT_MAX
+#define SHM_PRIV_KEY_END ((INT_MAX / 2) + 1)
+
+#define SHM_PREFIX		"sysvshm-"
+#define SHM_DIR _PATH_DEV "shm/"
+
+/* The maximum number of characters in a shared memory segment file name.
+   32 is the max number of characters in a 128 bit number in hex.  */
+#if __WORDSIZE > 128
+#error Need to increase SHM_NAMEMAX.
+#else
+#define SHM_NAMEMAX (sizeof (SHM_PREFIX) - 1 + 32 + 1)
+#endif
+
+/* Use this with printf and its variants.  */
+#define SHM_NAMEPRI SHM_PREFIX "%0x"
+
+
+/* Adds a segment attachment.  */
+error_t __sysvshm_add (void *addr, size_t size);
+
+/* Removes a segment attachment.  Returns its size if found, or EINVAL
+   otherwise.  */
+error_t __sysvshm_remove (void *addr, size_t *size);
--- /dev/null
+++ b/sysdeps/mach/hurd/ftok.c
@@ -0,0 +1,43 @@
+/* Copyright (C) 1995, 1996, 2000, 2005 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, August 1995.
+
+   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 <sys/ipc.h>
+#include <sys/stat.h>
+
+
+/* In the Hurd, we use the second-to-most-significant bit as flag for
+   private keys.  We use a different order of the components so that
+   the biggest one---the inode number---is affected by this.  */
+
+key_t
+ftok (pathname, proj_id)
+     const char *pathname;
+     int proj_id;
+{
+  struct stat64 st;
+  key_t key;
+
+  if (__xstat64 (_STAT_VER, pathname, &st) < 0)
+    return (key_t) -1;
+
+  key = ((st.st_dev & 0xff) | ((proj_id & 0xff) << 8)
+	 | ((st.st_ino & 0x3fff) << 16));
+
+  return key;
+}
--- /dev/null
+++ b/sysdeps/mach/hurd/shmat.c
@@ -0,0 +1,82 @@
+/* SysV shmat for Hurd.
+   Copyright (C) 2005-2015 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <utime.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <assert.h>
+#include <sys/mman.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <sys/time.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "sysvshm.h"
+
+/* Attach the shared memory segment associated with SHMID to the data
+   segment of the calling process.  SHMADDR and SHMFLG determine how
+   and where the segment is attached.  */
+void *
+__shmat (int shmid, const void *shmaddr, int shmflg)
+{
+  error_t err;
+  char filename[sizeof (SHM_DIR) - 1 + SHM_NAMEMAX];
+  int fd;
+  void *addr;
+  struct stat statbuf;
+  int res;
+
+  sprintf (filename, SHM_DIR SHM_NAMEPRI, shmid);
+  fd = __open (filename, (shmflg & SHM_RDONLY) ? O_RDONLY : O_RDWR);
+  if (fd < 0)
+    {
+      if (errno == ENOENT)
+	errno = EINVAL;
+      return (void *) -1;
+    }
+
+  res = __fstat (fd, &statbuf);
+  if (res < 0)
+    {
+      err = errno;
+      __close (fd);
+      errno = err;
+      return (void *) -1;
+    }
+
+  addr = __mmap ((void *) shmaddr, statbuf.st_size,
+		 PROT_READ | ((shmflg & SHM_RDONLY) ? 0 : PROT_WRITE),
+		 MAP_SHARED, fd, 0);
+  __close (fd);
+  if (addr == MAP_FAILED)
+    return (void *) -1;
+
+  err = __sysvshm_add (addr, statbuf.st_size);
+  if (err)
+    {
+      __munmap (addr, statbuf.st_size);
+      errno = err;
+      return (void *) -1;
+    }
+
+  return addr;
+}
+
+weak_alias(__shmat, shmat)
--- /dev/null
+++ b/sysdeps/mach/hurd/shmctl.c
@@ -0,0 +1,132 @@
+/* Copyright (C) 2005 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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "sysvshm.h"
+
+/* Provide operations to control over shared memory segments.  */
+int
+__shmctl (int id, int cmd, struct shmid_ds *buf)
+{
+  error_t err = 0;
+  int fd;
+  int res;
+  char filename[sizeof (SHM_DIR) - 1 + SHM_NAMEMAX];
+  struct stat statbuf;
+
+  sprintf (filename, SHM_DIR SHM_NAMEPRI, id);
+  /* SysV requires read access for IPC_STAT.  */
+  fd = __open (filename, O_NORW);
+  if (fd < 0)
+    {
+      if (errno == ENOENT)
+	errno = EINVAL;
+      return -1;
+    }
+
+  res = __fstat (fd, &statbuf);
+  if (res < 0)
+    {
+      err = errno;
+      __close (fd);
+      errno = err;
+      return -1;
+    }
+
+  switch (cmd)
+    {
+    case IPC_STAT:
+
+      buf->shm_perm.__key = id;
+      buf->shm_perm.uid = statbuf.st_uid;
+      buf->shm_perm.gid = statbuf.st_gid;
+
+      /* We do not support the creator.  */
+      buf->shm_perm.cuid = statbuf.st_uid;
+      buf->shm_perm.cgid = statbuf.st_gid;
+
+      /* We just want the protection bits.  */
+      buf->shm_perm.mode = statbuf.st_mode & 0777;
+      /* Hopeless.  We do not support a sequence number.  */
+      buf->shm_perm.__seq = statbuf.st_ino;
+      buf->shm_segsz = statbuf.st_size;
+
+      /* Hopeless.  We do not support any of these.  */
+      buf->shm_atime = statbuf.st_atime;
+      buf->shm_dtime = statbuf.st_mtime;
+      /* Well, this comes at least close.  */
+      buf->shm_ctime = statbuf.st_ctime;
+
+      /* We do not support the PID.  */
+      buf->shm_cpid = 0;
+      buf->shm_lpid = 0;
+
+      if (statbuf.st_mode & S_IMMAP0)
+        buf->shm_nattch = 0;
+      else
+        /* 42 is the answer.  Of course this is bogus, but for most
+	   applications, this should be fine.  */
+        buf->shm_nattch = 42;
+
+      break;
+
+    case IPC_SET:
+      if (statbuf.st_uid != buf->shm_perm.uid
+	  || statbuf.st_gid != buf->shm_perm.gid)
+	{
+	  res = __fchown (fd,
+			  (statbuf.st_uid != buf->shm_perm.uid)
+			  ? buf->shm_perm.uid : -1,
+			  (statbuf.st_gid != buf->shm_perm.gid)
+			  ? buf->shm_perm.gid : -1);
+	  if (res < 0)
+	    err = errno;
+	}
+
+      if (!err && statbuf.st_mode & 0777 != buf->shm_perm.mode & 0777)
+	{
+	  res = __fchmod (fd, (statbuf.st_mode & ~0777)
+			  | (buf->shm_perm.mode & 0777));
+	  if (res < 0)
+	    err = errno;
+	}
+      break;
+
+    case IPC_RMID:
+      res = __unlink (filename);
+      /* FIXME: Check error (mapping ENOENT to EINVAL).  */
+      break;
+
+    default:
+      err = EINVAL;
+    }
+
+  __close (fd);
+  errno = err;
+  return err ? -1 : 0;
+}
+
+weak_alias(__shmctl, shmctl)
--- /dev/null
+++ b/sysdeps/mach/hurd/shmdt.c
@@ -0,0 +1,51 @@
+/* Copyright (C) 2005 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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <stdio.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <assert.h>
+#include <sys/mman.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <sys/time.h>
+#include <sys/stat.h>
+
+#include "sysvshm.h"
+
+/* Detach shared memory segment starting at address specified by
+   SHMADDR from the caller's data segment.  */
+int
+__shmdt (const void *shmaddr)
+{
+  error_t err;
+  size_t size;
+
+  err = __sysvshm_remove ((void *) shmaddr, &size);
+  if (err)
+    {
+      errno = err;
+      return -1;
+    }
+
+  __munmap ((void *) shmaddr, size);
+  return 0;
+}
+
+weak_alias(__shmdt, shmdt)
--- /dev/null
+++ b/sysdeps/mach/hurd/shmget.c
@@ -0,0 +1,242 @@
+/* Copyright (C) 2005 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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/shm.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <limits.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <hurd/fd.h>
+
+#include "sysvshm.h"
+
+/* Create a new shared memory segment file without linking it into the
+   filesystem.  Return the directory and file ports in R_DIR and R_FILE.  */
+static error_t
+create_shm_file (size_t size, int flags, file_t *r_dir, file_t *r_file)
+{
+  error_t err;
+  file_t dir;
+  file_t file;
+
+  flags &= 0777;
+
+  /* Get a port to the directory that will contain the file.  */
+  dir = __file_name_lookup (SHM_DIR, 0, 0);
+  if (dir == MACH_PORT_NULL)
+    return errno;
+
+  /* Create an unnamed file in the directory.  */
+  err = __dir_mkfile (dir, O_RDWR, flags, &file);
+  if (err)
+    {
+      __mach_port_deallocate (__mach_task_self (), dir);
+      return err;
+    }
+
+  err = __file_set_size (file, size);
+  if (err)
+    {
+      __mach_port_deallocate (__mach_task_self (), file);
+      __mach_port_deallocate (__mach_task_self (), dir);
+
+      return err;
+    }
+
+  *r_dir = dir;
+  *r_file = file;
+
+  return 0;
+}
+
+
+/* Open the shared memory segment *R_KEY and return a file descriptor
+   to it in R_FD.  If KEY is IPC_PRIVATE, use a private key and return
+   it in R_KEY.  */
+static error_t
+get_exclusive (int shmflags, size_t size, key_t *r_key, int *r_fd)
+{
+  error_t err;
+  file_t dir;
+  file_t file;
+  char filename[SHM_NAMEMAX];
+  key_t key = *r_key;
+  bool is_private;
+
+  /* Create the shared memory segment.  */
+  err = create_shm_file (size, shmflags, &dir, &file);
+  if (err)
+    return err;
+
+  if (key == IPC_PRIVATE)
+    {
+      is_private = true;
+      key = SHM_PRIV_KEY_START;
+
+      /* Try to link the shared memory segment into the filesystem
+	 (exclusively).  Private segments have negative keys.  */
+      do
+	{
+	  sprintf (filename, SHM_NAMEPRI, key);
+	  err = __dir_link (dir, file, filename, 1);
+	  if (!err)
+	    {
+	      /* We are done.  */
+	      *r_key = key;
+	      break;
+	    }
+	  else if (err == EEXIST)
+	    {
+	      /* Check if we ran out of keys.  If not, try again with new
+		 key.  */
+	      if (key == SHM_PRIV_KEY_END)
+		err = ENOSPC;
+	      else
+		err = 0;
+
+	      key--;
+	    }
+	}
+      while (!err);
+    }
+  else
+    {
+      /* Try to link the shared memory segment into the filesystem
+	 (exclusively) under the given key.  */
+      sprintf (filename, SHM_NAMEPRI, key);
+      err = __dir_link (dir, file, filename, 1);
+    }
+
+  __mach_port_deallocate (__mach_task_self (), dir);
+
+  if (!err)
+    {
+      int fd;
+
+      /* Get a file descriptor for that port.  */
+      fd = _hurd_intern_fd (file, O_RDWR, 1); /* dealloc on error */
+      if (fd < 0)
+	err = errno;
+      else
+	*r_fd = fd;
+    }
+
+  return err;
+}
+
+
+/* Open the shared memory segment KEY (creating it if it doesn't yet
+   exist) and return a file descriptor to it in R_FD.  */
+static error_t
+get_shared (int shmflags, size_t size, key_t key, int *r_fd)
+{
+  error_t err = 0;
+  char filename[sizeof (SHM_DIR) - 1 + SHM_NAMEMAX];
+  int fd = -1;
+  sprintf (filename, SHM_DIR SHM_NAMEPRI, key);
+
+  do
+    {
+      fd = __open (filename, O_NORW, shmflags & 0777);
+
+      if (fd < 0 && errno != ENOENT)
+	/* We give up.  */
+	return errno;
+      else if (fd >= 0)
+	{
+	  int res;
+	  struct stat statbuf;
+
+	  /* Check the size (we only need to do this if we did not
+	     create the shared memory segment file ourselves).  */
+	  res = __fstat (fd, &statbuf);
+	  if (res < 0)
+	    {
+	      err = errno;
+	      __close (fd);
+	      return err;
+	    }
+
+	  if (statbuf.st_size < size)
+	    {
+	      __close (fd);
+	      return EINVAL;
+	    }
+	}
+      else
+	{
+	  /* The memory segment doesn't exist.  */
+	  if (shmflags & IPC_CREAT)
+	    {
+	      /* Try to create it exclusively.  */
+	      err = get_exclusive (shmflags, size, &key, &fd);
+	      if (err == EEXIST)
+		/* If somebody created it in the meanwhile, just try again.  */
+		err = 0;
+	    }
+	  else
+	    err = ENOENT;
+	}
+    }
+  while (fd < 0 && !err);
+
+  if (!err)
+    *r_fd = fd;
+  else
+    *r_fd = -1;
+
+  return err;
+}
+
+/* Return an identifier for an shared memory segment of at least size
+   SIZE which is associated with KEY.  */
+int
+__shmget (key_t key, size_t size, int shmflags)
+{
+  error_t err;
+  int fd;
+
+  if (key == IPC_PRIVATE || shmflags & IPC_EXCL)
+    /* An exclusive shared memory segment must be created.  */
+    err = get_exclusive (shmflags, size, &key, &fd);
+  else
+    err = get_shared (shmflags, size, key, &fd);
+
+  if (err)
+    {
+      errno = err;
+      return -1;
+    }
+
+  /* From here, we can't fail.  That's important, as otherwise we
+     would need to unlink the file if we created it (in that case, the
+     code above would have to be changed to pass a "created" flag down
+     to the caller).  */
+
+  __close (fd);
+
+  return key;
+}
+
+weak_alias(__shmget, shmget)
--- a/sysdeps/mach/hurd/bits/posix_opt.h
+++ b/sysdeps/mach/hurd/bits/posix_opt.h
@@ -68,8 +68,8 @@
 /* X/Open thread realtime support is not supported.  */
 #undef _XOPEN_REALTIME_THREADS
 
-/* XPG4.2 shared memory is not supported.  */
-#undef	_XOPEN_SHM
+/* XPG4.2 shared memory is supported.  */
+#define _XOPEN_SHM      1
 
 /* Tell we have POSIX threads.  */
 #define _POSIX_THREADS	200809L