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hurd: Implement SHM_ANON

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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 <bugaevc@gmail.com>
Message-Id: <20230130125216.6254-4-bugaevc@gmail.com>
This commit is contained in:
Sergey Bugaev 2023-01-30 15:52:16 +03:00 committed by Samuel Thibault
parent 65392c8478
commit a979b72747
3 changed files with 51 additions and 4 deletions
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25
posix/shm-directory.c
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@ -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);

5
rt/shm_open.c
View File

@ -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))

25
sysdeps/mach/hurd/bits/mman_ext.h Normal file
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@ -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 */