Replace two copies of readlink code with single gnulib version.

5 files changed, 49 insertions, 57 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index c2e28251cb0..5649c8819d3 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,15 @@
+2011-04-01  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Replace two copies of readlink code with single gnulib version.
+	The gnulib version avoids calling malloc in the usual case,
+	and on 64-bit hosts doesn't have some arbitrary 32-bit limits.
+	* fileio.c (Ffile_symlink_p): Use emacs_readlink.
+	* filelock.c (current_lock_owner): Likewise.
+	* lisp.h (READLINK_BUFSIZE, emacs_readlink): New function.
+	* sysdep.c: Include allocator.h, careadlinkat.h.
+	(emacs_no_realloc_allocator): New static constant.
+	(emacs_readlink): New function.
+
 2011-03-31  Juanma Barranquero  <lekktu@gmail.com>
 
 	* xdisp.c (redisplay_internal): Fix prototype.
diff --git a/src/fileio.c b/src/fileio.c
index 85431dfd5b1..552044f7272 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -2579,9 +2579,8 @@ points to a nonexistent file.  */)
 {
   Lisp_Object handler;
   char *buf;
-  int bufsize;
-  int valsize;
   Lisp_Object val;
+  char readlink_buf[READLINK_BUFSIZE];
 
   CHECK_STRING (filename);
   filename = Fexpand_file_name (filename, Qnil);
@@ -2594,36 +2593,15 @@ points to a nonexistent file.  */)
 
   filename = ENCODE_FILE (filename);
 
-  bufsize = 50;
-  buf = NULL;
-  do
-    {
-      bufsize *= 2;
-      buf = (char *) xrealloc (buf, bufsize);
-      memset (buf, 0, bufsize);
-
-      errno = 0;
-      valsize = readlink (SSDATA (filename), buf, bufsize);
-      if (valsize == -1)
-	{
-#ifdef ERANGE
-	  /* HP-UX reports ERANGE if buffer is too small.  */
-	  if (errno == ERANGE)
-	    valsize = bufsize;
-	  else
-#endif
-	    {
-	      xfree (buf);
-	      return Qnil;
-	    }
-	}
-    }
-  while (valsize >= bufsize);
+  buf = emacs_readlink (SSDATA (filename), readlink_buf);
+  if (! buf)
+    return Qnil;
 
-  val = make_string (buf, valsize);
+  val = build_string (buf);
   if (buf[0] == '/' && strchr (buf, ':'))
     val = concat2 (build_string ("/:"), val);
-  xfree (buf);
+  if (buf != readlink_buf)
+    xfree (buf);
   val = DECODE_FILE (val);
   return val;
 }
diff --git a/src/filelock.c b/src/filelock.c
index 2138eaa502b..13b27c72f19 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -396,36 +396,16 @@ within_one_second (time_t a, time_t b)
 static int
 current_lock_owner (lock_info_type *owner, char *lfname)
 {
-  int len, ret;
+  int ret;
+  size_t len;
   int local_owner = 0;
   char *at, *dot, *colon;
-  char *lfinfo = 0;
-  int bufsize = 50;
-  /* Read arbitrarily-long contents of symlink.  Similar code in
-     file-symlink-p in fileio.c.  */
-  do
-    {
-      bufsize *= 2;
-      lfinfo = (char *) xrealloc (lfinfo, bufsize);
-      errno = 0;
-      len = readlink (lfname, lfinfo, bufsize);
-#ifdef ERANGE
-      /* HP-UX reports ERANGE if the buffer is too small.  */
-      if (len == -1 && errno == ERANGE)
-	len = bufsize;
-#endif
-    }
-  while (len >= bufsize);
+  char readlink_buf[READLINK_BUFSIZE];
+  char *lfinfo = emacs_readlink (lfname, readlink_buf);
 
   /* If nonexistent lock file, all is well; otherwise, got strange error. */
-  if (len == -1)
-    {
-      xfree (lfinfo);
-      return errno == ENOENT ? 0 : -1;
-    }
-
-  /* Link info exists, so `len' is its length.  Null terminate.  */
-  lfinfo[len] = 0;
+  if (!lfinfo)
+    return errno == ENOENT ? 0 : -1;
 
   /* Even if the caller doesn't want the owner info, we still have to
      read it to determine return value, so allocate it.  */
@@ -441,7 +421,8 @@ current_lock_owner (lock_info_type *owner, char *lfname)
   dot = strrchr (lfinfo, '.');
   if (!at || !dot)
     {
-      xfree (lfinfo);
+      if (lfinfo != readlink_buf)
+	xfree (lfinfo);
       return -1;
     }
   len = at - lfinfo;
@@ -467,7 +448,8 @@ current_lock_owner (lock_info_type *owner, char *lfname)
   owner->host[len] = 0;
 
   /* We're done looking at the link info.  */
-  xfree (lfinfo);
+  if (lfinfo != readlink_buf)
+    xfree (lfinfo);
 
   /* On current host?  */
   if (STRINGP (Fsystem_name ())
diff --git a/src/lisp.h b/src/lisp.h
index 85838d111db..63f346f6a25 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3340,6 +3340,8 @@ extern int emacs_open (const char *, int, int);
 extern int emacs_close (int);
 extern int emacs_read (int, char *, unsigned int);
 extern int emacs_write (int, const char *, unsigned int);
+enum { READLINK_BUFSIZE = 1024 };
+extern char *emacs_readlink (const char *, char [READLINK_BUFSIZE]);
 #ifndef HAVE_MEMSET
 extern void *memset (void *, int, size_t);
 #endif
diff --git a/src/sysdep.c b/src/sysdep.c
index 1bb400421f0..a165a9ca52f 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -31,6 +31,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #endif /* HAVE_LIMITS_H */
 #include <unistd.h>
 
+#include <allocator.h>
+#include <careadlinkat.h>
 #include <ignore-value.h>
 
 #include "lisp.h"
@@ -1866,6 +1868,22 @@ emacs_write (int fildes, const char *buf, unsigned int nbyte)
     }
   return (bytes_written);
 }
+
+static struct allocator const emacs_norealloc_allocator =
+  { xmalloc, NULL, xfree, memory_full };
+
+/* Get the symbolic link value of FILENAME.  Return a pointer to a
+   NUL-terminated string.  If readlink fails, return NULL and set
+   errno.  If the value fits in INITIAL_BUF, return INITIAL_BUF.
+   Otherwise, allocate memory and return a pointer to that memory.  If
+   memory allocation fails, diagnose and fail without returning.  If
+   successful, store the length of the symbolic link into *LINKLEN.  */
+char *
+emacs_readlink (char const *filename, char initial_buf[READLINK_BUFSIZE])
+{
+  return careadlinkat (AT_FDCWD, filename, initial_buf, READLINK_BUFSIZE,
+		       &emacs_norealloc_allocator, careadlinkatcwd);
+}
 
 #ifdef USG
 /*