add directory study

study/linux-travel/MINIX-1.5/1.5/Source/commands/printroot.c

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+/* printroot - print root device on stdout	Author: Bruce Evans */
+
+/* This program figures out what the root device is by doing a stat on it, and
+ * then searching /dev until it finds an entry with the same device number.
+ * A typical use (probably the only use) is in /etc/rc for initializing
+ * /etc/mtab, as follows:
+ *
+ *	/usr/bin/printroot >/etc/mtab
+ *
+ *  9 Dec     1989 - clean up for 1.5 - full prototypes (BDE)
+ * 15 October 1989 - avoid ACK cc bugs (BDE):
+ *		   - sizeof "foo" is 2 (from wrong type char *) instead of 4
+ *		   - char foo[10] = "bar"; allocates 4 bytes instead of 10
+ *  1 October 1989 - Minor changes by Andy Tanenbaum
+ */
+
+#include <sys/types.h>
+#include <sys/dir.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static char DEV_PATH[] = "/dev/";	/* #define would step on sizeof bug */
+static char MESSAGE[] =	" is root device\n";	/* ditto */
+#define UNKNOWN_DEV	"/dev/unknown"
+#define ROOT		"/"
+
+#ifdef __STDC__
+static void done(char *name, int status);
+#else
+static void done();
+#endif
+
+int main(argc, argv)
+int argc;
+char **argv;
+{
+  struct direct dir;
+  int fd;
+  struct stat filestat, rootstat;
+  static char namebuf[sizeof DEV_PATH + NAME_MAX];
+
+  if (stat(ROOT, &rootstat) == 0 && (fd = open(DEV_PATH, O_RDONLY)) >= 0) {
+	while (read(fd, (char *) &dir, sizeof dir) == sizeof dir) {
+		if (dir.d_ino == 0) continue;
+		strcpy(namebuf, DEV_PATH);
+
+		/* If next does not null-terminate, last in buf does it. */
+		strncat(namebuf, dir.d_name, NAME_MAX);
+		if (stat(namebuf, &filestat) != 0) continue;
+		if ((filestat.st_mode & S_IFMT) != S_IFBLK) continue;
+		if (filestat.st_rdev != rootstat.st_dev) continue;
+		done(namebuf, 0);
+	}
+  }
+  done(UNKNOWN_DEV, 1);
+  return 0;			/* not reached */
+}
+
+static void done(name, status)
+char *name;
+int status;
+{
+  write(1, name, strlen(name));
+  write(1, MESSAGE, sizeof MESSAGE - 1);
+  exit(status);
+}