feat(filesystem): 引入Umount系统调用 (#719)

* feat(filesystem): 引入Umount系统调用

* 将所有ENOSYS误用更正

* 修复了一个使同一个挂载点可以挂载2个文件系统的bug

* 统一注释，增强程序稳定性，统一接口。注意：Umount时在fatfs的路径要使用大写，此受限于当前文件系统设计。

user/apps/test_ramfs/.gitignore

@@ -0,0 +1 @@
+test_ramfs

user/apps/test_ramfs/Makefile

@@ -0,0 +1,20 @@
+ifeq ($(ARCH), x86_64)
+	CROSS_COMPILE=x86_64-linux-musl-
+else ifeq ($(ARCH), riscv64)
+	CROSS_COMPILE=riscv64-linux-musl-
+endif
+
+CC=$(CROSS_COMPILE)gcc
+
+.PHONY: all
+all: main.c
+	$(CC) -static -o test_ramfs main.c
+
+.PHONY: install clean
+install: all
+	mv test_ramfs $(DADK_CURRENT_BUILD_DIR)/test_ramfs
+
+clean:
+	rm test_ramfs *.o
+
+fmt:

user/apps/test_ramfs/main.c

@@ -0,0 +1,115 @@
+// #include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/mount.h>
+
+#define MAX_PATH_LENGTH 100
+#define MAX_DIR_DEPTH 4
+
+
+int main(int argc, char const* argv[]) {
+
+    if (mkdir("/SOME", 0777) == -1) {
+        perror("Failed to create directory under /some");
+        return 1;
+    }
+
+    // Create a directory under /SOME/RAMFS
+    if (mkdir("/SOME/RAMFS", 0777) == -1) {
+        perror("Failed to create directory under /SOME/RAMFS");
+        return 1;
+    }
+
+    // Mount the first ramfs at /SOME/RAMFS
+    if (mount("", "/SOME/RAMFS", "ramfs", 0, NULL) == -1) {
+        perror("Failed to mount ramfs at /SOME/RAMFS");
+        return 1;
+    }
+
+    if (mkdir("/SOME/RAMFS/some", 0777) == -1) {
+        perror("Failed to create directory under /SOME/RAMFS/some");
+        return 1;
+    }
+
+    puts("Success mkdir /SOME/RAMFS/some");
+
+    // Create a directory under /SOME/RAMFS/some/another
+    if (mkdir("/SOME/RAMFS/some/another", 0777) == -1) {
+        perror("Failed to create directory under /SOME/RAMFS/some/another");
+        return 1;
+    }
+
+    puts("Success mkdir /SOME/RAMFS/some/another");
+
+    if (mount("", "/SOME/RAMFS/some/another", "ramfs", 0, NULL) == -1) {
+        perror("Failed to mount ramfs at /SOME/RAMFS/some/another");
+        return 1;
+    }
+
+    puts("Success mount on /SOME/RAMFS/some/another");
+
+    if (mkdir("/SOME/RAMFS/some/another/just_another", 0777) == -1) {
+        perror("Failed to create directory under /SOME/RAMFS/some/another");
+        return 1;
+    }
+
+    puts("Success mkdir /SOME/RAMFS/some/another/just_another");
+
+    if (mount("", "/SOME/RAMFS/some/another/just_another", "ramfs", 0, NULL) == -1) {
+        perror("Failed to mount ramfs at /SOME/RAMFS/some/another");
+        return 1;
+    }
+
+    puts("Success mount on /SOME/RAMFS/some/another/just_another");
+
+    // Write files under /SOME/RAMFS and /SOME/RAMFS/some/another
+    FILE* file1 = fopen("/SOME/RAMFS/file1.txt", "w");
+    if (file1 == NULL) {
+        perror("Failed to open /SOME/RAMFS/file1.txt");
+        return 1;
+    }
+    fprintf(file1, "This is file1.txt\n");
+    fclose(file1);
+
+    FILE* file2 = fopen("/SOME/RAMFS/some/another/file2.txt", "w");
+    if (file2 == NULL) {
+        perror("Failed to open /SOME/RAMFS/some/another/file2.txt");
+        return 1;
+    }
+    fprintf(file2, "This is file2.txt\n");
+    fclose(file2);
+
+    FILE* file3 = fopen("/SOME/RAMFS/some/another/just_another/file3.txt", "w+");
+    if (file3 == NULL) {
+        perror("Failed to open /SOME/RAMFS/some/another/just_another/file3.txt");
+        return 1;
+    }
+    fprintf(file3, "Multi mount behave well.\n");
+    // print file3.txt
+    char buffer[100];
+    fseek(file3, 0, SEEK_SET);
+    fread(buffer, 1, 100, file3);
+    printf("file3.txt content: %s\n", buffer);
+    fclose(file3);
+
+    // test umount with flags ( use umount2 )
+    if (umount("/SOME/RAMFS/some/another/just_another") == -1) {
+        perror("Failed to umount ramfs at /SOME/RAMFS/some/another/just_another");
+        return 1;
+    }
+
+    puts("Successful umount /SOME/RAMFS/some/another/just_another");
+
+    // delete just_another
+    if (rmdir("/SOME/RAMFS/some/another/just_another") == -1) {
+        perror("Failed to delete /SOME/RAMFS/some/another/just_another");
+        return 1;
+    }
+
+    return 0;
+}