+/* pwd.c
+
+ Prints the absolute name of the present working directory. */
+
+#include <syscall.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+
+static bool getcwd (char *cwd, size_t cwd_size);
+
+int
+main (void)
+{
+ char cwd[128];
+ if (getcwd (cwd, sizeof cwd))
+ {
+ printf ("%s\n", cwd);
+ return 0;
+ }
+ else
+ {
+ printf ("error\n");
+ return 1;
+ }
+}
+\f
+/* Stores the inode number for FILE_NAME in *INUM.
+ Returns true if successful, false if the file could not be
+ opened. */
+static bool
+get_inumber (const char *file_name, int *inum)
+{
+ int fd = open (file_name);
+ if (fd >= 0)
+ {
+ *inum = inumber (fd);
+ close (fd);
+ return true;
+ }
+ else
+ return false;
+}
+
+/* Prepends PREFIX to the characters stored in the final *DST_LEN
+ bytes of the DST_SIZE-byte buffer that starts at DST.
+ Returns true if successful, false if adding that many
+ characters, plus a null terminator, would overflow the buffer.
+ (No null terminator is actually added or depended upon, but
+ its space is accounted for.) */
+static bool
+prepend (const char *prefix,
+ char *dst, size_t *dst_len, size_t dst_size)
+{
+ size_t prefix_len = strlen (prefix);
+ if (prefix_len + *dst_len + 1 <= dst_size)
+ {
+ *dst_len += prefix_len;
+ memcpy ((dst + dst_size) - *dst_len, prefix, prefix_len);
+ return true;
+ }
+ else
+ return false;
+}
+
+/* Stores the current working directory, as a null-terminated
+ string, in the CWD_SIZE bytes in CWD.
+ Returns true if successful, false on error. Errors include
+ system errors, directory trees deeper than MAX_LEVEL levels,
+ and insufficient space in CWD. */
+static bool
+getcwd (char *cwd, size_t cwd_size)
+{
+ size_t cwd_len = 0;
+
+#define MAX_LEVEL 20
+ char name[MAX_LEVEL * 3 + 1 + READDIR_MAX_LEN + 1];
+ char *namep;
+
+ int child_inum;
+
+ /* Make sure there's enough space for at least "/". */
+ if (cwd_size < 2)
+ return false;
+
+ /* Get inumber for current directory. */
+ if (!get_inumber (".", &child_inum))
+ return false;
+
+ namep = name;
+ for (;;)
+ {
+ int parent_inum, parent_fd;
+
+ /* Compose "../../../..", etc., in NAME. */
+ if ((namep - name) > MAX_LEVEL * 3)
+ return false;
+ *namep++ = '.';
+ *namep++ = '.';
+ *namep = '\0';
+
+ /* Open directory. */
+ parent_fd = open (name);
+ if (parent_fd < 0)
+ return false;
+ *namep++ = '/';
+
+ /* If parent and child have the same inumber,
+ then we've arrived at the root. */
+ parent_inum = inumber (parent_fd);
+ if (parent_inum == child_inum)
+ break;
+
+ /* Find name of file in parent directory with the child's
+ inumber. */
+ for (;;)
+ {
+ int test_inum;
+ if (!readdir (parent_fd, namep) || !get_inumber (name, &test_inum))
+ {
+ close (parent_fd);
+ return false;
+ }
+ if (test_inum == child_inum)
+ break;
+ }
+ close (parent_fd);
+
+ /* Prepend "/name" to CWD. */
+ if (!prepend (namep - 1, cwd, &cwd_len, cwd_size))
+ return false;
+
+ /* Move up. */
+ child_inum = parent_inum;
+ }
+
+ /* Finalize CWD. */
+ if (cwd_len > 0)
+ {
+ /* Move the string to the beginning of CWD,
+ and null-terminate it. */
+ memmove (cwd, (cwd + cwd_size) - cwd_len, cwd_len);
+ cwd[cwd_len] = '\0';
+ }
+ else
+ {
+ /* Special case for the root. */
+ strlcpy (cwd, "/", cwd_size);
+ }
+
+ return true;
+}
projects / pintos-anon / commitdiff