call CheckDiskSpace() before pre-allocating space

- even if we are allowed to fail pre-allocating, it's better to check
  for sufficient space before calling AllocateFileRange() and if we
  are out of disk space return with error()
- the above change allows us to remove the CheckDiskSpace() check
  in CBlock::AcceptBlock()

src/main.cpp

@@ -1914,6 +1914,7 @@ bool FindBlockPos(CDiskBlockPos &pos, unsigned int nAddSize, unsigned int nHeigh
         unsigned int nOldChunks = (pos.nPos + BLOCKFILE_CHUNK_SIZE - 1) / BLOCKFILE_CHUNK_SIZE;
         unsigned int nNewChunks = (infoLastBlockFile.nSize + BLOCKFILE_CHUNK_SIZE - 1) / BLOCKFILE_CHUNK_SIZE;
         if (nNewChunks > nOldChunks) {
+            if (CheckDiskSpace(nNewChunks * BLOCKFILE_CHUNK_SIZE - pos.nPos)) {
                 FILE *file = OpenBlockFile(pos);
                 if (file) {
                     printf("Pre-allocating up to position 0x%x in blk%05u.dat\n", nNewChunks * BLOCKFILE_CHUNK_SIZE, pos.nFile);
@@ -1921,6 +1922,9 @@ bool FindBlockPos(CDiskBlockPos &pos, unsigned int nAddSize, unsigned int nHeigh
                     fclose(file);
                 }
             }
+            else
+                return error("FindBlockPos() : out of disk space");
+        }
     }
 
     if (!pblocktree->WriteBlockFileInfo(nLastBlockFile, infoLastBlockFile))
@@ -1956,6 +1960,7 @@ bool FindUndoPos(int nFile, CDiskBlockPos &pos, unsigned int nAddSize)
     unsigned int nOldChunks = (pos.nPos + UNDOFILE_CHUNK_SIZE - 1) / UNDOFILE_CHUNK_SIZE;
     unsigned int nNewChunks = (nNewSize + UNDOFILE_CHUNK_SIZE - 1) / UNDOFILE_CHUNK_SIZE;
     if (nNewChunks > nOldChunks) {
+        if (CheckDiskSpace(nNewChunks * UNDOFILE_CHUNK_SIZE - pos.nPos)) {
             FILE *file = OpenUndoFile(pos);
             if (file) {
                 printf("Pre-allocating up to position 0x%x in rev%05u.dat\n", nNewChunks * UNDOFILE_CHUNK_SIZE, pos.nFile);
@@ -1963,6 +1968,9 @@ bool FindUndoPos(int nFile, CDiskBlockPos &pos, unsigned int nAddSize)
                 fclose(file);
             }
         }
+        else
+            return error("FindUndoPos() : out of disk space");
+    }
 
     return true;
 }
@@ -2086,12 +2094,8 @@ bool CBlock::AcceptBlock(CDiskBlockPos *dbp)
     // Write block to history file
     unsigned int nBlockSize = ::GetSerializeSize(*this, SER_DISK, CLIENT_VERSION);
     CDiskBlockPos blockPos;
-    if (dbp == NULL) {
-        if (!CheckDiskSpace(::GetSerializeSize(*this, SER_DISK, CLIENT_VERSION)))
-            return error("AcceptBlock() : out of disk space");
-    } else {
+    if (dbp != NULL)
         blockPos = *dbp;
-    }
     if (!FindBlockPos(blockPos, nBlockSize+8, nHeight, nTime, dbp != NULL))
         return error("AcceptBlock() : FindBlockPos failed");
     if (dbp == NULL)