libc: Implement memfd on top of tmpfs

https://man7.org/linux/man-pages/man2/memfd_create.2.html

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

include/fcntl.h

@@ -97,6 +97,8 @@
 #define F_SETOWN    13 /* Set pid that will receive SIGIO and SIGURG signals for fd */
 #define F_SETSIG    14 /* Set the signal to be sent */
 #define F_GETPATH   15 /* Get the path of the file descriptor(BSD/macOS) */
+#define F_ADD_SEALS 16 /* Add the bit-mask argument arg to the set of seals of the inode */
+#define F_GET_SEALS 17 /* Get (as the function result) the current set of seals of the inode */
 
 /* For posix fcntl() and lockf() */
 
@@ -117,6 +119,14 @@
 #define DN_RENAME   4  /* A file was renamed */
 #define DN_ATTRIB   5  /* Attributes of a file were changed */
 
+/* Types of seals */
+
+#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 */
+#define F_SEAL_FUTURE_WRITE 0x0010 /* Prevent future writes while mapped */
+
 /* int creat(const char *path, mode_t mode);
  *
  * is equivalent to open with O_WRONLY|O_CREAT|O_TRUNC.

include/sys/memfd.h

@@ -0,0 +1,72 @@
+/****************************************************************************
+ * include/sys/memfd.h
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+#ifndef __INCLUDE_SYS_MEMFD_H
+#define __INCLUDE_SYS_MEMFD_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <fcntl.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#define MFD_CLOEXEC       O_CLOEXEC
+#define MFD_ALLOW_SEALING (1 << 16)
+#define MFD_HUGETLB       (1 << 17)
+
+#define MFD_HUGE_SHIFT   26
+#define MFD_HUGE_MASK    0x3f
+#define MFD_HUGE_64KB    (16 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_512KB   (19 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_1MB     (20 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_2MB     (21 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_8MB     (23 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_16MB    (24 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_32MB    (25 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_256MB   (28 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_512MB   (29 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_1GB     (30 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_2GB     (31 << MFD_HUGE_SHIFT)
+#define MFD_HUGE_16GB    (34 << MFD_HUGE_SHIFT)
+
+/****************************************************************************
+ * Public Function Prototypes
+ ****************************************************************************/
+
+#ifdef __cplusplus
+#define EXTERN extern "C"
+extern "C"
+{
+#else
+#define EXTERN extern
+#endif
+
+int memfd_create(FAR const char *name, unsigned int flags);
+
+#undef EXTERN
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __INCLUDE_SYS_MEMFD_H */

libs/libc/misc/Kconfig

@@ -62,6 +62,13 @@ config LIBC_ENVPATH
 		Use the contents of the common environment variable to locate executable
 		or library files.  Default: n
 
+config MEM_FD_VFS_PATH
+	string "Relative path to memfd storage"
+	default "memfd"
+	depends on FS_TMPFS
+	---help---
+		The relative path to where memfd will exist in the tmpfs namespace.
+
 config LIBC_ERR
 	bool "Support err() verr() verrx() warn() vwarn() vwarnx()"
 	default y

libs/libc/misc/Make.defs

@@ -22,7 +22,7 @@
 
 CSRCS += lib_mknod.c lib_umask.c lib_utsname.c lib_getrandom.c
 CSRCS += lib_xorshift128.c lib_tea_encrypt.c lib_tea_decrypt.c
-CSRCS += lib_cxx_initialize.c lib_impure.c
+CSRCS += lib_cxx_initialize.c lib_impure.c lib_memfd.c
 
 # Support for platforms that do not have long long types
 

libs/libc/misc/lib_memfd.c

@@ -0,0 +1,51 @@
+/****************************************************************************
+ * libs/libc/misc/lib_memfd.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <sys/memfd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#define MEM_FD_VFS_PATH CONFIG_LIBC_TMPDIR "/" CONFIG_MEM_FD_VFS_PATH "/%s"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+int memfd_create(FAR const char *name, unsigned int flags)
+{
+#ifdef CONFIG_FS_TMPFS
+  char path[PATH_MAX];
+
+  snprintf(path, sizeof(path), MEM_FD_VFS_PATH, name);
+  return open(path, O_RDWR | flags);
+#else
+  set_errno(ENOSYS);
+  return -1;
+#endif
+}