Token available locally but data must be read

• The buffer is recently stolen to satisfy other needs for buffer space.
• A previous write obtained a desired range token for more than it needed.

In either case, the kernel extension determines that the buffer is not available, suspends the application thread, and sends a message to a daemon service thread requesting the buffer. If the write call is for a full file system block, an empty buffer is allocated since the entire block is replaced. If the write call is for less than a full block and the rest of the block exists, the existing version of the block must be read and overlaid. If the write call creates a new block in the file, the daemon searches the allocation map for a block that is free and assigns it to the file. With both a buffer assigned and a block on the disk associated with the buffer, the write proceeds as it would in Buffer available in memory.