Hi there, Do let me know if I am asking these questions on the wrong forum. I'd like to write a QEMU block driver which forwards IO requests to a custom-built storage cluster.
I have seen Jeff Cody's presentation <http://bugnik.us/kvm2013> and also browsed the source code for sheepdog, nbd and gluster in the "block" directory and had a few questions to confirm or correct my understanding. 1) What is the difference between bdrv_open and bdrv_file_open function pointers in the BlockDriver ? 2) Is it possible to implement only a protocol driver without a format driver (the distinction that Jeff made in his presentation above) ? In other words, can I only set the "protocol_name" and not "format_name" in BlockDriver ? I'd like to support all image formats (qemu, raw, etc) without having to reimplement the logic for each. 3) The control flow for creating a file starts with the image format driver and later invokes the protocol driver. image_driver->bdrv_create() --> bdrv_create_file --> bdrv_find_protocol(filename) --> bdrv_create ---> Protocol_driver->bdrv_create() Is this the case for all functions? Does the read/write first flow through the image format driver before getting passed down to the protocol driver (possibly via some coroutine invoked from the block layer or virtio-blk ) ? Can someone give me a hint as to how I can trace the control flow ? thx -Sandeep
