+/* 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"
-#include <stdio.h>
+/* Some systems (eg Hurd) do 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.
*/
-
-#include <unistd.h>
-#include "libbb.h"
-
-extern char *xreadlink(const char *path)
+char* FAST_FUNC xmalloc_readlink(const char *path)
{
- static const int GROWBY = 80; /* how large we will grow strings by */
+ enum { GROWBY = 80 }; /* how large we will grow strings by */
char *buf = NULL;
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;
}
+
+/*
+ * 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)
+{
+/* NB: uclibc also defines __GLIBC__
+ * Therefore the test "if glibc, or uclibc >= 0.9.31" looks a bit weird:
+ */
+#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) */
+ return xstrdup(realpath(path, buf));
+#endif
+}
+
+char* FAST_FUNC xmalloc_realpath_coreutils(const char *path)
+{
+ char *buf;
+
+ errno = 0;
+ buf = xmalloc_realpath(path);
+ /*
+ * There is one case when "readlink -f" and
+ * "realpath" from coreutils succeed,
+ * even though file does not exist, such as:
+ * /tmp/file_does_not_exist
+ * (the directory must exist).
+ */
+ if (!buf && errno == ENOENT) {
+ char *last_slash = strrchr(path, '/');
+ if (last_slash) {
+ *last_slash++ = '\0';
+ buf = xmalloc_realpath(path);
+ if (buf) {
+ unsigned len = strlen(buf);
+ buf = xrealloc(buf, len + strlen(last_slash) + 2);
+ buf[len++] = '/';
+ strcpy(buf + len, last_slash);
+ }
+ } else {
+ char *target = xmalloc_readlink(path);
+ if (target) {
+ char *cwd;
+ if (target[0] == '/') {
+ /*
+ * $ ln -s /bin/qwe symlink # note: /bin is a link to /usr/bin
+ * $ readlink -f symlink
+ * /usr/bin/qwe/target_does_not_exist
+ * $ realpath symlink
+ * /usr/bin/qwe/target_does_not_exist
+ */
+ buf = xmalloc_realpath_coreutils(target);
+ free(target);
+ return buf;
+ }
+ /*
+ * $ ln -s target_does_not_exist symlink
+ * $ readlink -f symlink
+ * /CURDIR/target_does_not_exist
+ * $ realpath symlink
+ * /CURDIR/target_does_not_exist
+ */
+ cwd = xrealloc_getcwd_or_warn(NULL);
+ buf = concat_path_file(cwd, target);
+ free(cwd);
+ free(target);
+ return buf;
+ }
+ }
+ }
+
+ return buf;
+}
projects / oweals / busybox.git / blobdiff