Imported upstream 1.2.6

[nfs-utils.git] / utils / exportfs / exportfs.c

diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
index 7432a6592c8d0e69c60dfc69ececec56e92b1f34..a3323d733efb01c05a48c9bed8ae37f6dc40385d 100644 (file)
--- a/utils/exportfs/exportfs.c
+++ b/utils/exportfs/exportfs.c
@@ -16,6 +16,7 @@
 #include <sys/stat.h>
 #include <sys/vfs.h>
 #include <sys/stat.h>
+#include <sys/file.h>
 #include <unistd.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -43,6 +44,41 @@ static void  usage(const char *progname);
 static void    validate_export(nfs_export *exp);
 static int     matchhostname(const char *hostname1, const char *hostname2);
 static void    export_d_read(const char *dname);
+static void grab_lockfile(void);
+static void release_lockfile(void);
+
+static const char *lockfile = EXP_LOCKFILE;
+static int _lockfd = -1;
+
+/*
+ * If we aren't careful, changes made by exportfs can be lost
+ * when multiple exports process run at once:
+ *
+ *     exportfs process 1      exportfs process 2
+ *     ------------------------------------------
+ *     reads etab version A    reads etab version A
+ *     adds new export B       adds new export C
+ *     writes A+B              writes A+C
+ *
+ * The locking in support/export/xtab.c will prevent mountd from
+ * seeing a partially written version of etab, and will prevent 
+ * the two writers above from writing simultaneously and
+ * corrupting etab, but to prevent problems like the above we
+ * need these additional lockfile() routines.
+ */
+static void 
+grab_lockfile()
+{
+       _lockfd = open(lockfile, O_CREAT|O_RDWR, 0666);
+       if (_lockfd != -1) 
+               lockf(_lockfd, F_LOCK, 0);
+}
+static void 
+release_lockfile()
+{
+       if (_lockfd != -1)
+               lockf(_lockfd, F_ULOCK, 0);
+}
 
 int
 main(int argc, char **argv)
@@ -129,6 +165,13 @@ main(int argc, char **argv)
                        return 0;
                }
        }
+
+       /*
+        * Serialize things as best we can
+        */
+       grab_lockfile();
+       atexit(release_lockfile);
+
        if (f_export && ! f_ignore) {
                export_read(_PATH_EXPORTS);
                export_d_read(_PATH_EXPORTS_D);