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qemu treats blockjob bandwidth as a 64-bit number, in the units of bytes/second. But we stupidly modeled block job bandwidth after migration bandwidth, which in turn was an 'unsigned long' and therefore subject to 32-bit vs. 64-bit interpretations, and with a scale of MiB/s. Our code already has to convert between the two scales, and report overflow as appropriate; although this conversion currently lives in the monitor code. In fact, our conversion code limited things to 63 bits, because we checked against LLONG_MAX and reject what would be negative bandwidth if treated as signed. On the bright side, our use of MiB/s means that even with a 32-bit unsigned long, we still have no problem representing a bandwidth of 2GiB/s, which is starting to be more feasible as 10-gigabit or even faster interfaces are used. And once you get past the physical speeds of existing interfaces, any larger bandwidth number behaves the same - effectively unlimited. But on the low side, the granularity of 1MiB/s tuning is rather coarse. So the new virDomainBlockJob API decided to go with a direct 64-bit bytes/sec number instead of the scaled number that prior blockjob APIs had used. But there is no point in rounding this number to MiB/s just to scale it back to bytes/s for handing to qemu. In order to make future code sharing possible between the old virDomainBlockRebase and the new virDomainBlockCopy, this patch moves the scaling and overflow detection into the driver code. Several of the block job calls that can set speed are fed through a common interface, so it was easier to adjust all block jobs at once, for consistency. This patch is just code motion; there should be no user-visible change in behavior. * src/qemu/qemu_monitor.h (qemuMonitorBlockJob) (qemuMonitorBlockCommit, qemuMonitorDriveMirror): Change parameter type and scale. * src/qemu/qemu_monitor.c (qemuMonitorBlockJob) (qemuMonitorBlockCommit, qemuMonitorDriveMirror): Move scaling and overflow detection... * src/qemu/qemu_driver.c (qemuDomainBlockJobImpl) (qemuDomainBlockRebase, qemuDomainBlockCommit): ...here. (qemuDomainBlockCopy): Use bytes/sec. Signed-off-by: Eric Blake <eblake@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>