rt: Replace generic stub of shm_open with the posix version

Result of: git mv -f sysdeps/posix/shm_open.c rt
and manual removal of the _POSIX_MAPPED_FILES preprocessor condition.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 29 insertions, 5 deletions

diff --git a/rt/shm_open.c b/rt/shm_open.c
index e2bd25978a..a89aac4102 100644
--- a/rt/shm_open.c
+++ b/rt/shm_open.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 2000-2021 Free Software Foundation, Inc.
+/* shm_open -- open a POSIX shared memory object.  Generic POSIX file version.
+   Copyright (C) 2001-2021 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
@@ -16,13 +17,36 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <errno.h>
-#include <sys/mman.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <shm-directory.h>
+#include <unistd.h>
 
 /* Open shared memory object.  */
 int
 shm_open (const char *name, int oflag, mode_t mode)
 {
-  __set_errno (ENOSYS);
-  return -1;
+  struct shmdir_name dirname;
+  if (__shm_get_name (&dirname, name, false) != 0)
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
+  oflag |= O_NOFOLLOW | O_CLOEXEC;
+
+  /* Disable asynchronous cancellation.  */
+  int state;
+  pthread_setcancelstate (PTHREAD_CANCEL_DISABLE, &state);
+
+  int fd = open (dirname.name, oflag, mode);
+  if (fd == -1 && __glibc_unlikely (errno == EISDIR))
+    /* It might be better to fold this error with EINVAL since
+       directory names are just another example for unsuitable shared
+       object names and the standard does not mention EISDIR.  */
+    __set_errno (EINVAL);
+
+  pthread_setcancelstate (state, NULL);
+
+  return fd;
 }
-stub_warning (shm_open)