Overview -------- This patch series adds image streaming support for QED image files. Other image formats can also be supported in the future.
Image streaming populates the file in the background while the guest is running. This makes it possible to start the guest before its image file has been fully provisioned. Example use cases include: * Providing small virtual appliances for download that can be launched immediately but provision themselves in the background. * Reducing guest provisioning time by creating local image files but backing them with shared master images which will be streamed. When image streaming is enabled, the unallocated regions of the image file are populated with the data from the backing file. This occurs in the background and the guest can perform regular I/O in the meantime. Once the entire backing file has been streamed, the image no longer requires a backing file and will drop its reference. Example invocation ------------------ $ # my_fedora.qed is a tiny file initially but will be streamed when the guest starts $ ./qemu-img create -f qed -o backing_file=fedora-14.img my_fedora.qed Formatting 'my_fedora.qed', fmt=qed size=10737418240 backing_file='fedora-14.img' cluster_size=0 table_size=0 $ # run the guest and stream fedora-14.img into my_fedora.qed $ x86_64-softmmu/qemu-system-x86_64 -m 512 -enable-kvm -drive if=virtio,file=my_fedora.qed,cache=none,stream=on Details on changes ------------------ Image streaming introduces a new bdrv_aio_copy_backing() interface. Block drivers that implement this interface support streaming. This function scans for an unallocated cluster and populates it with data from the backing file. The details of populating the image file are actually best implemented as a copy-on-read operation. Copy-on-read means that a read request will populate the image file if it needs to fetch data from the backing file. The copy-on-read feature can be used outside the context of streaming and this patch series therefore introduces the -drive copy-on-read=on option for that purpose. Two new monitor interfaces are introduced: block_stream and query-block-stream. They can be used to start streaming a block device and to poll progress. QMP events are raised on completion and failure so that polling is not required. Adam Litke <a...@us.ibm.com> has implemented the libvirt APIs for image streaming: http://permalink.gmane.org/gmane.comp.emulators.libvirt/40080 Patches 1-2 qemu-config: },{ -> }, { to please checkpatch.pl block: add -drive copy-on-read=on|off These patches add the -drive copy-on-read=on|off option although no block driver supports it yet. Patches 3-7 qed: replace is_write with flags field qed: extract qed_start_allocating_write() qed: make qed_aio_write_alloc() reusable qed: add support for copy-on-read qed: avoid deadlock on emulated synchronous I/O These patches add copy-on-read support to the QED block driver. Patches 8-11 qerror: add qerror_from_args() to create qerror objects block: add bdrv_aio_copy_backing() qmp: add QMP support for stream commands block: add -drive stream=on|off These patches add the -drive stream=on|off and monitor commands for image streaming. Patch 12 qed: intelligent streaming implementation This patch adds image streaming support to the QED block driver. Patch 13 trace: trace bdrv_aio_readv/writev error paths This patch adds helpful trace events for block layer debugging. v1: * -drive copy-on-read=on|off,stream=on|off instead of image header bits * Latest libvirt API compatibility * Workaround and assert for synchronous I/O emulation deadlock Anthony Liguori (4): qed: add support for copy-on-read block: add bdrv_aio_copy_backing() qmp: add QMP support for stream commands qed: intelligent streaming implementation Stefan Hajnoczi (9): qemu-config: },{ -> }, { to please checkpatch.pl block: add -drive copy-on-read=on|off qed: replace is_write with flags field qed: extract qed_start_allocating_write() qed: make qed_aio_write_alloc() reusable qed: avoid deadlock on emulated synchronous I/O qerror: add qerror_from_args() to create qerror objects block: add -drive stream=on|off trace: trace bdrv_aio_readv/writev error paths block.c | 66 +++++++++- block.h | 6 + block/qed.c | 363 ++++++++++++++++++++++++++++++++++++++++++++++-------- block/qed.h | 8 +- block_int.h | 3 + blockdev.c | 286 +++++++++++++++++++++++++++++++++++++++++++ blockdev.h | 6 + hmp-commands.hx | 24 ++++- monitor.c | 23 ++++ monitor.h | 1 + qemu-config.c | 166 +++++++++++++------------ qemu-options.hx | 12 ++- qerror.c | 30 +++++ qerror.h | 12 ++ qmp-commands.hx | 68 ++++++++++ trace-events | 10 ++- 16 files changed, 940 insertions(+), 144 deletions(-) -- 1.7.5.3
