On Wed, Jul 18, 2012 at 9:51 AM, Wenchao Xia <xiaw...@linux.vnet.ibm.com> wrote: > /* sync access */ > int qbdrvs_read(BlockDriverState *bs, int64_t sector_num, > uint8_t *buf, int nb_sectors); > int qbdrvs_write(BlockDriverState *bs, int64_t sector_num, > const uint8_t *buf, int nb_sectors);
Whether to provide sync and/or async access is a key question. Synchronous APIs are great for writing dedicated tools like dd, cp, convert, etc. Asynchronous APIs are essential for integrating image file I/O into event-driven programs like libvirt. Here, the ability to do other things while image file I/O is in progress is a requirement. It may also be necessary to cancel or timeout if an operation is not making progress or the user decides to stop it. I think we need to provide both sync and async. Libraries like libssh2 and libcurl already do this so their APIs can be used as a starting point for async I/O. Stefan
