Stop using /dev/null to find out the serialized object length

Now the rdbSave* functions return the number of bytes written (or
required to write) in serializing a Redis object, writing to /dev/null
and using ftell (which doesn't work on FreeBSD) isn't needed anymore.

src/debug.c

@@ -216,7 +216,7 @@ void debugCommand(redisClient *c) {
                 "encoding:%s serializedlength:%lld "
                 "lru:%d lru_seconds_idle:%lu",
                 (void*)val, val->refcount,
-                strenc, (long long) rdbSavedObjectLen(val,NULL),
+                strenc, (long long) rdbSavedObjectLen(val),
                 val->lru, estimateObjectIdleTime(val));
         } else {
             vmpointer *vp = (vmpointer*) val;

src/rdb.c

@@ -389,20 +389,15 @@ int rdbSaveObject(FILE *fp, robj *o) {
  * the rdbSaveObject() function. Currently we use a trick to get
  * this length with very little changes to the code. In the future
  * we could switch to a faster solution. */
-off_t rdbSavedObjectLen(robj *o, FILE *fp) {
-    int nwritten;
-    if (fp == NULL) fp = server.devnull;
-    rewind(fp);
-
-    /* Determining the saved length of an object should never return -1 */
-    redisAssert((nwritten = rdbSaveObject(fp,o)) != -1);
-    return nwritten;
+off_t rdbSavedObjectLen(robj *o) {
+    int len = rdbSaveObject(NULL,o);
+    redisAssert(len != -1);
+    return len;
 }
 
 /* Return the number of pages required to save this object in the swap file */
-off_t rdbSavedObjectPages(robj *o, FILE *fp) {
-    off_t bytes = rdbSavedObjectLen(o,fp);
-
+off_t rdbSavedObjectPages(robj *o) {
+    off_t bytes = rdbSavedObjectLen(o);
     return (bytes+(server.vm_page_size-1))/server.vm_page_size;
 }
 

src/redis.c

@@ -814,11 +814,6 @@ void initServer() {
     setupSigSegvAction();
 
     server.mainthread = pthread_self();
-    server.devnull = fopen("/dev/null","w");
-    if (server.devnull == NULL) {
-        redisLog(REDIS_WARNING, "Can't open /dev/null: %s", server.neterr);
-        exit(1);
-    }
     server.clients = listCreate();
     server.slaves = listCreate();
     server.monitors = listCreate();

src/redis.h

@@ -481,7 +481,6 @@ struct redisServer {
     dict *pubsub_channels; /* Map channels to list of subscribed clients */
     list *pubsub_patterns; /* A list of pubsub_patterns */
     /* Misc */
-    FILE *devnull;
     unsigned lruclock:22;        /* clock incrementing every minute, for LRU */
     unsigned lruclock_padding:10;
 };
@@ -743,8 +742,8 @@ int rdbSaveBackground(char *filename);
 void rdbRemoveTempFile(pid_t childpid);
 int rdbSave(char *filename);
 int rdbSaveObject(FILE *fp, robj *o);
-off_t rdbSavedObjectPages(robj *o, FILE *fp);
-off_t rdbSavedObjectLen(robj *o, FILE *fp);
+off_t rdbSavedObjectLen(robj *o);
+off_t rdbSavedObjectPages(robj *o);
 robj *rdbLoadObject(int type, FILE *fp);
 void backgroundSaveDoneHandler(int statloc);
 

src/vm.c

@@ -263,7 +263,7 @@ int vmWriteObjectOnSwap(robj *o, off_t page) {
  * If we can't find enough contiguous empty pages to swap the object on disk
  * NULL is returned. */
 vmpointer *vmSwapObjectBlocking(robj *val) {
-    off_t pages = rdbSavedObjectPages(val,NULL);
+    off_t pages = rdbSavedObjectPages(val);
     off_t page;
     vmpointer *vp;
 
@@ -821,9 +821,7 @@ void *IOThreadEntryPoint(void *arg) {
             vmpointer *vp = (vmpointer*)j->id;
             j->val = vmReadObjectFromSwap(j->page,vp->vtype);
         } else if (j->type == REDIS_IOJOB_PREPARE_SWAP) {
-            FILE *fp = fopen("/dev/null","w+");
-            j->pages = rdbSavedObjectPages(j->val,fp);
-            fclose(fp);
+            j->pages = rdbSavedObjectPages(j->val);
         } else if (j->type == REDIS_IOJOB_DO_SWAP) {
             if (vmWriteObjectOnSwap(j->val,j->page) == REDIS_ERR)
                 j->canceled = 1;