zvfs: 重构核心读写逻辑并新增 POSIX hook；引入目录元数据与伪 fd；分离创建、打开、关闭、删除的逻辑；

func_test.c

@@ -0,0 +1,40 @@
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+    const char *path = "/zvfs/func_test.dat";
+    if (argc > 2 && strcmp(argv[1], "-f") == 0) path = argv[2];
+    setenv("ZVFS_ROOT", "/zvfs", 0);
+
+    printf("open: %s\n", path);
+    int fd = open(path, O_CREAT|O_RDWR, 0644);
+    if (fd < 0) { perror("open"); return 1; }
+
+    const char *msg = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    ssize_t w = write(fd, msg, strlen(msg));
+    if (w < 0) { perror("write"); return 2; }
+    printf("write: %zd\n", w);
+
+    /* Rewind by closing and reopening for read */
+    close(fd);
+    fd = open(path, O_RDONLY);
+    if (fd < 0) { perror("open R"); return 3; }
+
+    char buf[256]; memset(buf, 0, sizeof(buf));
+    ssize_t r = read(fd, buf, sizeof(buf));
+    if (r < 0) { perror("read"); return 4; }
+    printf("read: %zd bytes: %.*s\n", r, (int)r, buf);
+    close(fd);
+
+    if (unlink(path) != 0) { perror("unlink"); return 5; }
+    printf("unlink: ok\n");
+    return 0;
+}