This adds a special SHM_ANON value that can be passed into shm_open ()
in place of a name. When called in this way, shm_open () will create a
new anonymous shared memory file. The file will be created in the same
way that other shared memory files are created (i.e., under /dev/shm/),
except that it is not given a name and therefore cannot be reached from
the file system, nor by other calls to shm_open (). This is accomplished
by utilizing O_TMPFILE.
This is intended to be compatible with FreeBSD's API of the same name.
Signed-off-by: Sergey Bugaev <buga...@gmail.com>
---
posix/shm-directory.c | 25 +++++++++++++++++++++----
rt/shm_open.c | 5 +++++
sysdeps/mach/hurd/bits/mman_ext.h | 25 +++++++++++++++++++++++++
3 files changed, 51 insertions(+), 4 deletions(-)
create mode 100644 sysdeps/mach/hurd/bits/mman_ext.h
diff --git a/posix/shm-directory.c b/posix/shm-directory.c
index 47e2355d..86d9fd8e 100644
--- a/posix/shm-directory.c
+++ b/posix/shm-directory.c
@@ -23,17 +23,34 @@
#include <alloc_buffer.h>
#include <shm-directory.h>
#include <string.h>
+#include <sys/mman.h>
+#include <fcntl.h>
int
__shm_get_name (struct shmdir_name *result, const char *name, bool sem_prefix)
{
+ struct alloc_buffer buffer;
+ size_t namelen;
+
+ buffer = alloc_buffer_create (result->name, sizeof (result->name));
+ alloc_buffer_copy_bytes (&buffer, SHMDIR, strlen (SHMDIR));
+
+#if defined (SHM_ANON) && defined (O_TMPFILE)
+ if (name == SHM_ANON)
+ {
+ /* For SHM_ANON, we want shm_open () to pass O_TMPFILE to open (),
+ with SHMDIR itself as the path. So, leave it at that. */
+ alloc_buffer_add_byte (&buffer, 0);
+ if (alloc_buffer_has_failed (&buffer))
+ return -1;
+ return 0;
+ }
+#endif
+
while (name[0] == '/')
++name;
- size_t namelen = strlen (name);
+ namelen = strlen (name);
- struct alloc_buffer buffer
- = alloc_buffer_create (result->name, sizeof (result->name));
- alloc_buffer_copy_bytes (&buffer, SHMDIR, strlen (SHMDIR));
if (sem_prefix)
alloc_buffer_copy_bytes (&buffer, "sem.", strlen ("sem."));
alloc_buffer_copy_bytes (&buffer, name, namelen + 1);
diff --git a/rt/shm_open.c b/rt/shm_open.c
index 48970bbc..6c1f4d60 100644
--- a/rt/shm_open.c
+++ b/rt/shm_open.c
@@ -23,6 +23,7 @@
#include <shlib-compat.h>
#include <shm-directory.h>
#include <unistd.h>
+#include <sys/mman.h>
/* Open shared memory object. */
int
@@ -36,6 +37,10 @@ __shm_open (const char *name, int oflag, mode_t mode)
}
oflag |= O_NOFOLLOW | O_CLOEXEC;
+#if defined (SHM_ANON) && defined (O_TMPFILE)
+ if (name == SHM_ANON)
+ oflag |= O_TMPFILE;
+#endif
int fd = __open64_nocancel (dirname.name, oflag, mode);
if (fd == -1 && __glibc_unlikely (errno == EISDIR))
diff --git a/sysdeps/mach/hurd/bits/mman_ext.h
b/sysdeps/mach/hurd/bits/mman_ext.h
new file mode 100644
index 00000000..f022826e
--- /dev/null
+++ b/sysdeps/mach/hurd/bits/mman_ext.h
@@ -0,0 +1,25 @@
+/* System-specific extensions of <sys/mman.h>, Hurd version.
+ Copyright (C) 2022 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/>. */
+
+#ifndef _SYS_MMAN_H
+# error "Never include <bits/mman_ext.h> directly; use <sys/mman.h> instead."
+#endif
+
+#ifdef __USE_GNU
+# define SHM_ANON ((const char *) 1)
+#endif /* __USE_GNU */
--
2.39.1
