/* vi: set sw=4 ts=4: */
/*
- * xreadlink.c - safe implementation of readlink.
- * Returns a NULL on failure...
+ * xreadlink.c - safe implementation of readlink.
+ * Returns a NULL on failure...
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
*/
#include "libbb.h"
+/* some systems (eg Hurd) does not have MAXSYMLINKS definition,
+ * set it to some reasonable value if it isn't defined */
+#ifndef MAXSYMLINKS
+# define MAXSYMLINKS 20
+#endif
+
/*
* NOTE: This function returns a malloced char* that you will have to free
- * yourself. You have been warned.
+ * yourself.
*/
-
-char *xreadlink(const char *path)
+char* FAST_FUNC xmalloc_readlink(const char *path)
{
enum { GROWBY = 80 }; /* how large we will grow strings by */
int bufsize = 0, readsize = 0;
do {
- buf = xrealloc(buf, bufsize += GROWBY);
- readsize = readlink(path, buf, bufsize); /* 1st try */
+ bufsize += GROWBY;
+ buf = xrealloc(buf, bufsize);
+ readsize = readlink(path, buf, bufsize);
if (readsize == -1) {
- bb_perror_msg("%s", path);
free(buf);
return NULL;
}
- }
- while (bufsize < readsize + 1);
+ } while (bufsize < readsize + 1);
buf[readsize] = '\0';
return buf;
}
-char *xmalloc_realpath(const char *path)
+/*
+ * This routine is not the same as realpath(), which
+ * canonicalizes the given path completely. This routine only
+ * follows trailing symlinks until a real file is reached and
+ * returns its name. If the path ends in a dangling link or if
+ * the target doesn't exist, the path is returned in any case.
+ * Intermediate symlinks in the path are not expanded -- only
+ * those at the tail.
+ * A malloced char* is returned, which must be freed by the caller.
+ */
+char* FAST_FUNC xmalloc_follow_symlinks(const char *path)
+{
+ char *buf;
+ char *lpc;
+ char *linkpath;
+ int bufsize;
+ int looping = MAXSYMLINKS + 1;
+
+ buf = xstrdup(path);
+ goto jump_in;
+
+ while (1) {
+ linkpath = xmalloc_readlink(buf);
+ if (!linkpath) {
+ /* not a symlink, or doesn't exist */
+ if (errno == EINVAL || errno == ENOENT)
+ return buf;
+ goto free_buf_ret_null;
+ }
+
+ if (!--looping) {
+ free(linkpath);
+ free_buf_ret_null:
+ free(buf);
+ return NULL;
+ }
+
+ if (*linkpath != '/') {
+ bufsize += strlen(linkpath);
+ buf = xrealloc(buf, bufsize);
+ lpc = bb_get_last_path_component_strip(buf);
+ strcpy(lpc, linkpath);
+ free(linkpath);
+ } else {
+ free(buf);
+ buf = linkpath;
+ jump_in:
+ bufsize = strlen(buf) + 1;
+ }
+ }
+}
+
+char* FAST_FUNC xmalloc_readlink_or_warn(const char *path)
+{
+ char *buf = xmalloc_readlink(path);
+ if (!buf) {
+ /* EINVAL => "file: Invalid argument" => puzzled user */
+ const char *errmsg = "not a symlink";
+ int err = errno;
+ if (err != EINVAL)
+ errmsg = strerror(err);
+ bb_error_msg("%s: cannot read link: %s", path, errmsg);
+ }
+ return buf;
+}
+
+char* FAST_FUNC xmalloc_realpath(const char *path)
{
-#ifdef __GLIBC__
+#if defined(__GLIBC__) || \
+ (defined(__UCLIBC__) && UCLIBC_VERSION >= KERNEL_VERSION(0, 9, 31))
/* glibc provides a non-standard extension */
+ /* new: POSIX.1-2008 specifies this behavior as well */
return realpath(path, NULL);
#else
char buf[PATH_MAX+1];
- /* on error returns NULL (xstrdup(NULL) ==NULL) */
+ /* on error returns NULL (xstrdup(NULL) == NULL) */
return xstrdup(realpath(path, buf));
#endif
}