win32: changes to stat(2) implementationFRP-4716-g31467ddfc

- Use repeated calls to readlink(2) rather than xmalloc_realpath()
  when asked to follow symlinks.

- Drop the non-standard feature that caused readlink(2) to return
  only the target string length.

This improves compatibility with BusyBox on Linux at a cost of
16-32 bytes.

1 files changed, 22 insertions, 15 deletions

diff --git a/win32/mingw.c b/win32/mingw.c
index 01d935eb9..72165cdd7 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -625,40 +625,51 @@ static int count_subdirs(const char *pathname)
  */
 static int do_lstat(int follow, const char *file_name, struct mingw_stat *buf)
 {
-        int err = EINVAL;
+        int err;
         WIN32_FILE_ATTRIBUTE_DATA fdata;
         WIN32_FIND_DATAA findbuf;
         DWORD low, high;
         off64_t size;
-        ssize_t len;
+        char lname[PATH_MAX];
 #if ENABLE_FEATURE_EXTRA_FILE_DATA
         DWORD flags;
         BY_HANDLE_FILE_INFORMATION hdata;
         HANDLE fh;
 #endif
 
-        while (file_name && !(err=get_file_attr(file_name, &fdata))) {
+        while (!(err=get_file_attr(file_name, &fdata))) {
                 buf->st_ino = 0;
                 buf->st_uid = DEFAULT_UID;
                 buf->st_gid = DEFAULT_GID;
                 buf->st_dev = buf->st_rdev = 0;
-                buf->st_tag =
-                        get_symlink_data(fdata.dwFileAttributes, file_name, &findbuf);
+                buf->st_attr = fdata.dwFileAttributes;
+                buf->st_tag = get_symlink_data(buf->st_attr, file_name, &findbuf);
 
                 if (buf->st_tag) {
+                        ssize_t len = readlink(file_name, lname, PATH_MAX);
+                        if (len < 0) {
+                                err = errno;
+                                break;
+                        } else if (len == PATH_MAX) {
+                                errno = ENAMETOOLONG;
+                                break;
+                        }
+
                         if (follow) {
                                 /* The file size and times are wrong when Windows follows
-                                 * a symlink.  Use the canonicalized path instead. */
-                                err = errno;
-                                file_name = auto_string(xmalloc_realpath(file_name));
+                                 * a symlink.  Use the symlink target instead. */
+                                if (follow++ > MAXSYMLINKS) {
+                                        err = ELOOP;
+                                        break;
+                                }
+                                lname[len] = '\0';
+                                file_name = lname;
                                 continue;
                         }
 
                         /* Get the contents of a symlink, not its target. */
                         buf->st_mode = S_IFLNK|S_IRWXU|S_IRWXG|S_IRWXO;
-                        buf->st_attr = fdata.dwFileAttributes;
-                        len = readlink(file_name, NULL, 0);
-                        buf->st_size = len == -1 ? 0 : len;
+                        buf->st_size = len;
                         buf->st_atim = filetime_to_timespec(&(findbuf.ftLastAccessTime));
                         buf->st_mtim = filetime_to_timespec(&(findbuf.ftLastWriteTime));
                         buf->st_ctim = filetime_to_timespec(&(findbuf.ftCreationTime));
@@ -666,7 +677,6 @@ static int do_lstat(int follow, const char *file_name, struct mingw_stat *buf)
                 else {
                         /* The file is not a symlink. */
                         buf->st_mode = file_attr_to_st_mode(fdata.dwFileAttributes);
-                        buf->st_attr = fdata.dwFileAttributes;
                         if (S_ISREG(buf->st_mode) &&
                                         !(buf->st_attr & FILE_ATTRIBUTE_DEVICE) &&
                                         (has_exe_suffix(file_name) || has_exec_format(file_name)))
@@ -1524,7 +1534,6 @@ char *realpath(const char *path, char *resolved_path)
 }
 
 #define SRPB rptr->SymbolicLinkReparseBuffer
-/* Non-standard feature:  if buf is NULL just return the length. */
 ssize_t readlink(const char *pathname, char *buf, size_t bufsiz)
 {
         HANDLE h;
@@ -1552,8 +1561,6 @@ ssize_t readlink(const char *pathname, char *buf, size_t bufsiz)
                 }
 
                 if (name) {
-                        if (buf == NULL)
-                                return len;
                         if (len > bufsiz)
                                 len = bufsiz;
                         len = WideCharToMultiByte(CP_ACP, 0, name, len, buf, bufsiz, 0, 0);