syscall: add memfd_create() (v3)

v2: Follow the kerndat style that "features" are described
just by global boolean variables.

v3: give NULL as a name to get EFAULT if memfd_create is supported
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

arch/arm/syscall.def

@@ -96,3 +96,4 @@ kcmp				272	378	(pid_t pid1, pid_t pid2, int type, unsigned long idx1, unsigned
 openat				56	322	(int dirfd, const char *pathname, int flags, mode_t mode)
 mkdirat				34	323	(int dirfd, const char *pathname, mode_t mode)
 unlinkat			35	328	(int dirfd, const char *pathname, int flags)
+memfd_create			279	385	(const char *name, unsigned int flags)

arch/x86/syscall-x86-64.def

@@ -96,3 +96,4 @@ __NR_prlimit64		302		sys_prlimit64		(pid_t pid, unsigned int resource, const str
 __NR_open_by_handle_at	304		sys_open_by_handle_at	(int mountdirfd, struct file_handle *handle, int flags)
 __NR_setns		308		sys_setns		(int fd, int nstype)
 __NR_kcmp		312		sys_kcmp		(pid_t pid1, pid_t pid2, int type, unsigned long idx1, unsigned long idx2)
+__NR_memfd_create	319		sys_memfd_create	(const char *name, unsigned int flags)

include/kerndat.h

@@ -24,4 +24,6 @@ extern u64 zero_page_pfn;
 struct stat;
 extern struct stat *kerndat_get_devpts_stat(void);
 
+extern bool memfd_is_supported;
+
 #endif /* __CR_KERNDAT_H__ */

kerndat.c

@@ -13,6 +13,7 @@
 #include "mem.h"
 #include "compiler.h"
 #include "sysctl.h"
+#include "syscall.h"
 #include "asm/types.h"
 #include "cr_options.h"
 #include "util.h"
@@ -220,6 +221,25 @@ int get_last_cap(void)
 	return sysctl_op(req, CTL_READ);
 }
 
+bool memfd_is_supported;
+static bool kerndat_has_memfd_create(void)
+{
+	int ret;
+
+	ret = sys_memfd_create(NULL, 0);
+
+	if (ret == -ENOSYS)
+		memfd_is_supported = false;
+	else if (ret == -EFAULT)
+		memfd_is_supported = true;
+	else {
+		pr_err("Unexpected error %d from memfd_create(NULL, 0)\n", ret);
+		return -1;
+	}
+
+	return 0;
+}
+
 int kerndat_init(void)
 {
 	int ret;
@@ -231,6 +251,8 @@ int kerndat_init(void)
 		ret = init_zero_page_pfn();
 	if (!ret)
 		ret = get_last_cap();
+	if (!ret)
+		ret = kerndat_has_memfd_create();
 
 	return ret;
 }