Hi, This patch gives userspace ability to prevent underlying file of loop device to be sparse. Currently, if loop device is 'trimmed' (BLKDISCARD), then underlying file will always become sparse and disk space freed. This behaviour is good for thin provisioning but not good for preallocated disk images. This patch introduces LO_FLAGS_NO_DEALLOC flag, which will write zeroes to underlying file instead of punching holes when BLKDISCARD is requested. Thus reducing file fragmentation of preallocated disk images and improve performance. I will also submit patches to util-linux to provide userspace support if this patch is merged. Changes in V1->V2: Renamed NODEALLOC to NO_DEALLOC, to avoid confusion between NO_DEALLOC and NODE_ALLOC. Suggested by Jens Axboe. Best Regards, Zhang Boyang
