areadlink, areadlinkat: rewrite in terms of careadlinkat

* lib/areadlink.c, lib/areadlinkat.c: Include careadlinkat.h
instead of errno.h, limits.h, stdint.h, stdlib.h, string.h, unistd.h.
(SSIZE_MAX, INITIAL_BUF_SIZE): Remove.
(malloc, realloc): Remove #undefs.
(areadlink, areadlinkat): Rewrite in terms of careadlinkat.
* modules/areadlink (Depends-on): Add careadlinkat.  Remove
readlink, ssize_t, stdint, unistd.
* modules/areadlinkat (Depends-on): Add careadlinkat.  Remove
areadlink, stdint.

careadlinkat: new module
* lib/allocator.h, lib/careadlinkat.h, lib/careadlinkat.c:
* modules/careadlinkat: New files, written by me with
a review and feedback from Ben Pfaff in
<http://lists.gnu.org/archive/html/bug-gnulib/2011-04/msg00008.html>.

1 files changed, 3 insertions, 83 deletions

diff --git a/lib/areadlinkat.c b/lib/areadlinkat.c
index a13c0e506d..2c227f36d9 100644
--- a/lib/areadlinkat.c
+++ b/lib/areadlinkat.c
@@ -25,101 +25,21 @@
 /* Specification.  */
 #include "areadlink.h"
 
-#include <errno.h>
-#include <limits.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-
-#ifndef SSIZE_MAX
-# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
-#endif
+#include "careadlinkat.h"
 
 #if HAVE_READLINKAT
 
-/* The initial buffer size for the link value.  A power of 2
-   detects arithmetic overflow earlier, but is not required.  */
-enum {
-  INITIAL_BUF_SIZE = 1024
-};
-
 /* Call readlinkat to get the symbolic link value of FILENAME relative to FD.
    Return a pointer to that NUL-terminated string in malloc'd storage.
    If readlinkat fails, return NULL and set errno (although failure to
    change directory will issue a diagnostic and exit).
-   If realloc fails, or if the link value is longer than SIZE_MAX :-),
+   If allocation fails, or if the link value is longer than SIZE_MAX :-),
    return NULL and set errno to ENOMEM.  */
 
 char *
 areadlinkat (int fd, char const *filename)
 {
-  /* Allocate the initial buffer on the stack.  This way, in the common
-     case of a symlink of small size, we get away with a single small malloc()
-     instead of a big malloc() followed by a shrinking realloc().  */
-  char initial_buf[INITIAL_BUF_SIZE];
-
-  char *buffer = initial_buf;
-  size_t buf_size = sizeof initial_buf;
-
-  while (1)
-    {
-      /* Attempt to read the link into the current buffer.  */
-       ssize_t link_length = readlinkat (fd, filename, buffer, buf_size);
-
-      /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
-         with errno == ERANGE if the buffer is too small.  */
-      if (link_length < 0 && errno != ERANGE)
-        {
-          if (buffer != initial_buf)
-            {
-              int saved_errno = errno;
-              free (buffer);
-              errno = saved_errno;
-            }
-          return NULL;
-        }
-
-      if ((size_t) link_length < buf_size)
-        {
-          buffer[link_length++] = '\0';
-
-          /* Return it in a chunk of memory as small as possible.  */
-          if (buffer == initial_buf)
-            {
-              buffer = (char *) malloc (link_length);
-              if (buffer == NULL)
-                /* errno is ENOMEM.  */
-                return NULL;
-              memcpy (buffer, initial_buf, link_length);
-            }
-          else
-            {
-              /* Shrink buffer before returning it.  */
-              if ((size_t) link_length < buf_size)
-                {
-                  char *smaller_buffer = (char *) realloc (buffer, link_length);
-
-                  if (smaller_buffer != NULL)
-                    buffer = smaller_buffer;
-                }
-            }
-          return buffer;
-        }
-
-      if (buffer != initial_buf)
-        free (buffer);
-      buf_size *= 2;
-      if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
-        {
-          errno = ENOMEM;
-          return NULL;
-        }
-      buffer = (char *) malloc (buf_size);
-      if (buffer == NULL)
-        /* errno is ENOMEM.  */
-        return NULL;
-    }
+  return careadlinkat (fd, filename, NULL, 0, NULL, readlinkat);
 }
 
 #else /* !HAVE_READLINKAT */