--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2006-11-20  Jim Meyering  <jim@meyering.net>
 
+	* lib/idcache.c: Restore most of the 2006-11-06 patch, so as to
+	continue using the flexible array member (thus, this module performs
+	half as many malloc calls), with the addition that...
+	(getgroup, getuser): Consistently record a non-match via an empty
+	"name" string, and map an empty string match to a NULL return value.
+	* modules/idcache (Depends-on): Re-add flexmember.
+
 	* lib/idcache.c (getuser): Remove all uses of the register keyword.
 	(getuidbyname, getgroup, getgidbyname): Likewise.
 

--- a/lib/idcache.c
+++ b/lib/idcache.c
@@ -19,6 +19,7 @@
 
 #include <config.h>
 
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
@@ -40,8 +41,8 @@
       uid_t u;
       gid_t g;
     } id;
-  char *name;
   struct userid *next;
+  char name[FLEXIBLE_ARRAY_MEMBER];
 };
 
 static struct userid *user_alist;
@@ -55,21 +56,31 @@
 getuser (uid_t uid)
 {
   struct userid *tail;
-  struct passwd *pwent;
+  struct userid *match = NULL;
 
   for (tail = user_alist; tail; tail = tail->next)
-    if (tail->id.u == uid)
-      return tail->name;
+    {
+      if (tail->id.u == uid)
+	{
+	  match = tail;
+	  break;
+	}
+    }
 
-  pwent = getpwuid (uid);
-  tail = xmalloc (sizeof *tail);
-  tail->id.u = uid;
-  tail->name = pwent ? xstrdup (pwent->pw_name) : NULL;
+  if (match == NULL)
+    {
+      struct passwd *pwent = getpwuid (uid);
+      char const *name = pwent ? pwent->pw_name : "";
+      match = xmalloc (offsetof (struct userid, name) + strlen (name) + 1);
+      match->id.u = uid;
+      strcpy (match->name, name);
 
-  /* Add to the head of the list, so most recently used is first.  */
-  tail->next = user_alist;
-  user_alist = tail;
-  return tail->name;
+      /* Add to the head of the list, so most recently used is first.  */
+      match->next = user_alist;
+      user_alist = match;
+    }
+
+  return match->name[0] ? match->name : NULL;
 }
 
 /* Translate USER to a UID, with cache.
@@ -104,8 +115,8 @@
     }
 #endif
 
-  tail = xmalloc (sizeof *tail);
-  tail->name = xstrdup (user);
+  tail = xmalloc (offsetof (struct userid, name) + strlen (user) + 1);
+  strcpy (tail->name, user);
 
   /* Add to the head of the list, so most recently used is first.  */
   if (pwent)
@@ -131,21 +142,31 @@
 getgroup (gid_t gid)
 {
   struct userid *tail;
-  struct group *grent;
+  struct userid *match = NULL;
 
   for (tail = group_alist; tail; tail = tail->next)
-    if (tail->id.g == gid)
-      return tail->name;
+    {
+      if (tail->id.g == gid)
+	{
+	  match = tail;
+	  break;
+	}
+    }
 
-  grent = getgrgid (gid);
-  tail = xmalloc (sizeof *tail);
-  tail->id.g = gid;
-  tail->name = grent ? xstrdup (grent->gr_name) : NULL;
+  if (match == NULL)
+    {
+      struct group *grent = getgrgid (gid);
+      char const *name = grent ? grent->gr_name : "";
+      match = xmalloc (offsetof (struct userid, name) + strlen (name) + 1);
+      match->id.g = gid;
+      strcpy (match->name, name);
 
-  /* Add to the head of the list, so most recently used is first.  */
-  tail->next = group_alist;
-  group_alist = tail;
-  return tail->name;
+      /* Add to the head of the list, so most recently used is first.  */
+      match->next = group_alist;
+      group_alist = match;
+    }
+
+  return match->name[0] ? match->name : NULL;
 }
 
 /* Translate GROUP to a GID, with cache.
@@ -172,7 +193,7 @@
   grent = getgrnam (group);
 #ifdef __DJGPP__
   /* We need to pretend to belong to group GROUP, to make
-     grp functions know about any arbitrary group name.  */
+     grp functions know about an arbitrary group name.  */
   if (!grent && strspn (group, digits) < strlen (group))
     {
       setenv ("GROUP", group, 1);
@@ -180,8 +201,8 @@
     }
 #endif
 
-  tail = xmalloc (sizeof *tail);
-  tail->name = xstrdup (group);
+  tail = xmalloc (offsetof (struct userid, name) + strlen (group) + 1);
+  strcpy (tail->name, group);
 
   /* Add to the head of the list, so most recently used is first.  */
   if (grent)

--- a/modules/idcache
+++ b/modules/idcache
@@ -6,6 +6,7 @@
 m4/idcache.m4
 
 Depends-on:
+flexmember
 xalloc
 
 configure.ac: