util: add linux-only memfd fallback

Implement memfd_create() fallback if not available in system libc.
memfd_create() is still not included in glibc today, atlhough it's been
available since Linux 3.17 in Oct 2014.

memfd has numerous advantages over traditional shm/mmap for ipc memory
sharing with fd handler, which we are going to make use of for
vhost-user logging memory in following patches.

The next patches are going to introduce helpers to use best practices of
memfd usage and provide some compatibility fallback. memfd.c is thus
temporarily useless and eventually empty if memfd_create() is provided
by the system.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Thibaut Collet <thibaut.collet@6wind.com>

3 files changed, 75 insertions, 0 deletions

diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
new file mode 100644
index 0000000000..8b1fe6ad66
--- /dev/null
+++ b/include/qemu/memfd.h
@@ -0,0 +1,20 @@
+#ifndef QEMU_MEMFD_H
+#define QEMU_MEMFD_H
+
+#include "config-host.h"
+
+#ifndef F_LINUX_SPECIFIC_BASE
+#define F_LINUX_SPECIFIC_BASE 1024
+#endif
+
+#ifndef F_ADD_SEALS
+#define F_ADD_SEALS (F_LINUX_SPECIFIC_BASE + 9)
+#define F_GET_SEALS (F_LINUX_SPECIFIC_BASE + 10)
+
+#define F_SEAL_SEAL     0x0001  /* prevent further seals from being set */
+#define F_SEAL_SHRINK   0x0002  /* prevent file from shrinking */
+#define F_SEAL_GROW     0x0004  /* prevent file from growing */
+#define F_SEAL_WRITE    0x0008  /* prevent writes */
+#endif
+
+#endif /* QEMU_MEMFD_H */
diff --git a/util/Makefile.objs b/util/Makefile.objs
index f217901161..bab1722fc8 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -6,6 +6,7 @@ util-obj-$(CONFIG_POSIX) += oslib-posix.o
 util-obj-$(CONFIG_POSIX) += qemu-openpty.o
 util-obj-$(CONFIG_POSIX) += qemu-thread-posix.o
 util-obj-$(CONFIG_WIN32) += event_notifier-win32.o
+util-obj-$(CONFIG_POSIX) += memfd.o
 util-obj-$(CONFIG_WIN32) += oslib-win32.o
 util-obj-$(CONFIG_WIN32) += qemu-thread-win32.o
 util-obj-y += envlist.o path.o module.o
diff --git a/util/memfd.c b/util/memfd.c
new file mode 100644
index 0000000000..c50969255f
--- /dev/null
+++ b/util/memfd.c
@@ -0,0 +1,54 @@
+/*
+ * memfd.c
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * QEMU library functions on POSIX which are shared between QEMU and
+ * the QEMU tools.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu/osdep.h"
+
+#include "qemu/memfd.h"
+
+#ifdef CONFIG_MEMFD
+#include <sys/memfd.h>
+#elif defined CONFIG_LINUX
+#include <sys/syscall.h>
+#include <asm/unistd.h>
+
+inline static int memfd_create(const char *name, unsigned int flags)
+{
+#ifdef __NR_memfd_create
+    return syscall(__NR_memfd_create, name, flags);
+#else
+    return -1;
+#endif
+}
+#endif
+
+#ifndef MFD_CLOEXEC
+#define MFD_CLOEXEC 0x0001U
+#endif
+
+#ifndef MFD_ALLOW_SEALING
+#define MFD_ALLOW_SEALING 0x0002U
+#endif