Describe dummy test model. Work on OpenFlow intro.

[openvswitch] / ovsdb / log.c

diff --git a/ovsdb/log.c b/ovsdb/log.c
index c0be5f5d6372f1ee08287c186b84cc8fef651566..b79535ac814b12b3073b6a66a7830888449cd394 100644 (file)
--- a/ovsdb/log.c
+++ b/ovsdb/log.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2009, 2010 Nicira Networks
+/* Copyright (c) 2009, 2010, 2011, 2012 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -43,6 +43,7 @@ enum ovsdb_log_mode {
 };
 
 struct ovsdb_log {
+    off_t prev_offset;
     off_t offset;
     char *name;
     struct lockfile *lockfile;
@@ -79,7 +80,7 @@ ovsdb_log_open(const char *name, enum ovsdb_log_open_mode open_mode,
         locking = open_mode != OVSDB_LOG_READ_ONLY;
     }
     if (locking) {
-        int retval = lockfile_lock(name, 0, &lockfile);
+        int retval = lockfile_lock(name, &lockfile);
         if (retval) {
             error = ovsdb_io_error(retval, "%s: failed to lock lockfile",
                                    name);
@@ -94,7 +95,16 @@ ovsdb_log_open(const char *name, enum ovsdb_log_open_mode open_mode,
     } else if (open_mode == OVSDB_LOG_READ_WRITE) {
         flags = O_RDWR;
     } else if (open_mode == OVSDB_LOG_CREATE) {
-        flags = O_RDWR | O_CREAT | O_EXCL;
+        if (stat(name, &s) == -1 && errno == ENOENT
+            && lstat(name, &s) == 0 && S_ISLNK(s.st_mode)) {
+            /* 'name' is a dangling symlink.  We want to create the file that
+             * the symlink points to, but POSIX says that open() with O_EXCL
+             * must fail with EEXIST if the named file is a symlink.  So, we
+             * have to leave off O_EXCL and accept the race. */
+            flags = O_RDWR | O_CREAT;
+        } else {
+            flags = O_RDWR | O_CREAT | O_EXCL;
+        }
     } else {
         NOT_REACHED();
     }
@@ -121,6 +131,7 @@ ovsdb_log_open(const char *name, enum ovsdb_log_open_mode open_mode,
     file->name = xstrdup(name);
     file->lockfile = lockfile;
     file->stream = stream;
+    file->prev_offset = 0;
     file->offset = 0;
     file->read_error = NULL;
     file->write_error = NULL;
@@ -284,9 +295,10 @@ ovsdb_log_read(struct ovsdb_log *file, struct json **jsonp)
         goto error;
     }
 
+    file->prev_offset = file->offset;
     file->offset = data_offset + data_length;
     *jsonp = json;
-    return 0;
+    return NULL;
 
 error:
     file->read_error = ovsdb_error_clone(error);
@@ -294,6 +306,22 @@ error:
     return error;
 }
 
+/* Causes the log record read by the previous call to ovsdb_log_read() to be
+ * effectively discarded.  The next call to ovsdb_log_write() will overwrite
+ * that previously read record.
+ *
+ * Calling this function more than once has no additional effect.
+ *
+ * This function is useful when ovsdb_log_read() successfully reads a record
+ * but that record does not make sense at a higher level (e.g. it specifies an
+ * invalid transaction). */
+void
+ovsdb_log_unread(struct ovsdb_log *file)
+{
+    assert(file->mode == OVSDB_LOG_READ);
+    file->offset = file->prev_offset;
+}
+
 struct ovsdb_error *
 ovsdb_log_write(struct ovsdb_log *file, struct json *json)
 {
@@ -353,7 +381,7 @@ ovsdb_log_write(struct ovsdb_log *file, struct json *json)
 
     file->offset += strlen(header) + length;
     free(json_string);
-    return 0;
+    return NULL;
 
 error:
     file->write_error = ovsdb_error_clone(error);
@@ -367,7 +395,7 @@ ovsdb_log_commit(struct ovsdb_log *file)
     if (fsync(fileno(file->stream))) {
         return ovsdb_io_error(errno, "%s: fsync failed", file->name);
     }
-    return 0;
+    return NULL;
 }
 
 /* Returns the current offset into the file backing 'log', in bytes.  This