write objects.precache in tmp file first, then move it

It's a good standard to do so and in fact, we do this already in several
places, ex. the status.dat. This ensures the file is ready and completly
written before it will be used.

The issue here is, that naemon starts without any issues if the precached file
is empty for any reason. Except it has zero hosts/services then and removes all
existing states/downtime/comments.

Signed-off-by: Sven Nierlein <[email protected]>

src/naemon/objects.c

@@ -11,6 +11,7 @@
 #include "logging.h"
 #include "globals.h"
 #include "nm_alloc.h"
+#include "utils.h"
 
 int __nagios_object_structure_version = CURRENT_OBJECT_STRUCTURE_VERSION;
 
@@ -20,17 +21,32 @@ int fcache_objects(char *cache_file)
 	FILE *fp = NULL;
 	time_t current_time = 0L;
 	unsigned int i;
+	char *tmp_file = NULL;
+	int fd = 0;
+	int result = OK;
 
 	/* some people won't want to cache their objects */
 	if (!cache_file || !strcmp(cache_file, "/dev/null"))
 		return OK;
 
 	time(&current_time);
 
+	nm_asprintf(&tmp_file, "%sXXXXXX", cache_file);
+	if (tmp_file == NULL)
+		return ERROR;
+
+	if ((fd = mkstemp(tmp_file)) == -1) {
+		nm_log(NSLOG_RUNTIME_ERROR, "Error: Unable to create temp file '%s' for writing object cache data: %s\n", tmp_file, strerror(errno));
+		nm_free(tmp_file);
+		return ERROR;
+	}
+
 	/* open the cache file for writing */
-	fp = fopen(cache_file, "w");
+	fp = (FILE *)fopen(tmp_file, "w");
 	if (fp == NULL) {
-		nm_log(NSLOG_CONFIG_WARNING, "Warning: Could not open object cache file '%s' for writing!\n", cache_file);
+		unlink(tmp_file);
+		nm_log(NSLOG_CONFIG_WARNING, "Warning: Could not open object cache data file '%s' for writing!\n", tmp_file);
+		nm_free(tmp_file);
 		return ERROR;
 	}
 
@@ -44,7 +60,6 @@ int fcache_objects(char *cache_file)
 	fprintf(fp, "# Created: %s", ctime(&current_time));
 	fprintf(fp, "########################################\n\n");
 
-
 	/* cache timeperiods */
 	for (i = 0; i < num_objects.timeperiods; i++)
 		fcache_timeperiod(fp, timeperiod_ary[i]);
@@ -109,7 +124,41 @@ int fcache_objects(char *cache_file)
 			fcache_hostescalation(fp, esclist->object_ptr);
 	}
 
-	fclose(fp);
+	/* reset file permissions */
+	fchmod(fd, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH);
+
+	/* flush the file to disk */
+	fflush(fp);
+
+	/* fsync the file so that it is completely written out before moving it */
+	fsync(fd);
+
+	/* close the temp file */
+	result = ferror(fp) | fclose(fp);
+
+	/* save/close was successful */
+	if (result == 0) {
+
+		result = OK;
+
+		/* move the temp file to the status log (overwrite the old status log) */
+		if (my_rename(tmp_file, cache_file)) {
+			unlink(tmp_file);
+			nm_log(NSLOG_RUNTIME_ERROR, "Error: Unable to update cache data file '%s': %s", cache_file, strerror(errno));
+			result = ERROR;
+		}
+	}
+
+	/* a problem occurred saving the file */
+	else {
+		result = ERROR;
+
+		/* remove temp file and log an error */
+		unlink(tmp_file);
+		nm_log(NSLOG_RUNTIME_ERROR, "Error: Unable to save cache data file: %s", strerror(errno));
+	}
+
+	nm_free(tmp_file);
 
-	return OK;
+	return result;
 }