enhance exportfs to use new cache/upcall stuff

[nfs-utils.git] / support / export / xtab.c

diff --git a/support/export/xtab.c b/support/export/xtab.c
index 3ef36610357209f06e73e184cff3fc48e1d177dc..d9265a24e078627725ea4319e89f43a72f5cb7d9 100644 (file)
--- a/support/export/xtab.c
+++ b/support/export/xtab.c
@@ -18,6 +18,8 @@
 #include "xio.h"
 #include "xlog.h"
 
+static void cond_rename(char *newfile, char *oldfile);
+
 static int
 xtab_read(char *xtab, int is_export)
 {
@@ -104,7 +106,7 @@ xtab_write(char *xtab, char *xtabtmp, int is_export)
        }
        endexportent();
 
-       rename(xtabtmp, xtab);
+       cond_rename(xtabtmp, xtab);
 
        xfunlock(lockid);
 
@@ -142,3 +144,46 @@ xtab_append(nfs_export *exp)
        exp->m_xtabent = 1;
 }
 
+/*
+ * rename newfile onto oldfile unless
+ * they are identical 
+ */
+static void cond_rename(char *newfile, char *oldfile)
+{
+       int nfd, ofd;
+       char nbuf[4096], obuf[4096];
+       int ncnt, ocnt;
+
+       nfd = open(newfile, 0);
+       if (nfd < 0)
+               return;
+       ofd = open(oldfile, 0);
+       if (ofd < 0) {
+               close(nfd);
+               rename(newfile, oldfile);
+               return;
+       }
+
+       do {
+               ncnt = read(nfd, nbuf, sizeof(nbuf));
+               if (ncnt < 0)
+                       break;
+               ocnt = read(ofd, obuf, sizeof(obuf));
+               if (ocnt < 0)
+                       break;
+               if (ncnt != ocnt)
+                       break;
+               if (ncnt == 0) {
+                       close(nfd);
+                       close(ofd);
+                       unlink(newfile);
+                       return;
+               }
+       } while (memcmp(obuf, nbuf, ncnt) == 0);
+
+       /* some mis-match */
+       close(nfd);
+       close(ofd);
+       rename(newfile, oldfile);
+       return;
+}