Some block devices (ZFS volume) may require BLKDISCARD and BLKZEROOUT
ioctls for discard and write_zeroes operations respectively.
There is no good way to probe whether fallocate is supported on a block
device. Arguably, punch_hole and write_zeroes are rare. Instead of
having a complex scheme for the IO uring backend, we force it to always
use ioctls. The code can be changed if the synchronized ioctls become a
performance issue.
Changes:
- Detect block devices at construction time
- Use BLKDISCARD ioctl for punch_hole (discard) on block devices
- Use BLKZEROOUT ioctl for write_zeroes on block devices
- Add BLKDISCARD/BLKZEROOUT to VirtioBlock seccomp whitelist
- Keep fallocate() path for regular files (no behavior change)
- Consolidate some helper functions to the new sparse module
Signed-off-by: Wei Liu <liuwe@microsoft.com>
