Re: [Qemu-devel] [PATCH v2 0/2] Dynamic module support for block drivers

["Denis V. Lunev" <den-lists@parallels.com>]

On 09/08/2015 04:53 PM, Marc Marí wrote:
> The current module infrastructure has been improved to enable dynamic module
> loading.
>
> This reduces the load time for very simple guests. For the following
> configuration (very loaded)
>
> ./configure --enable-sdl --enable-gtk --enable-vte --enable-curses \
>      --enable-vnc --enable-vnc-{jpeg,tls,sasl,png} --enable-virtfs \
>      --enable-brlapi --enable-curl --enable-fdt --enable-bluez \
>      --enable-kvm --enable-rdma --enable-uuid --enable-vde \
>      --enable-linux-aio --enable-cap-ng --enable-attr --enable-vhost-net \
>      --enable-vhost-scsi --enable-spice --enable-rbd --enable-libiscsi \
>      --enable-smartcard-nss --enable-guest-agent --enable-libusb \
>      --enable-usb-redir --enable-lzo --enable-snappy --enable-bzip2 \
>      --enable-seccomp --enable-coroutine-pool --enable-glusterfs \
>      --enable-tpm --enable-libssh2 --enable-vhdx --enable-numa \
>      --enable-tcmalloc --target-list=x86_64-softmmu
>
> With modules disabled, there are 142 libraries loaded at startup. Time is
> the following:
>   LD time: 0.065 seconds
>   QEMU time: 0.02 seconds
>   Total time: 0.085 seconds
>
> With this patch series and modules enabled, there are 128 libraries loaded
> at startup. Time is the following:
>   LD time: 0.02 seconds
>   QEMU time: 0.02 seconds
>   Total time: 0.04 seconds
>
> Where LD time is the time between the program startup and the jump to main,
> and QEMU time is the time between the start of main and the first kvm_entry.
>
> These results are just with a few block drivers, that were already a module.
> Adding more modules (block or not block) should be easy, and will reduce
> the load time even more.
>
> Marc Marí (2):
>    Add dynamic module loading for block drivers
>    Add dynamic generation of module_block.h
>
>   .gitignore                      |   1 +
>   Makefile                        |  10 ++-
>   block.c                         |  70 +++++++++++++++++++++
>   configure                       |   2 +-
>   include/qemu/module.h           |   3 +
>   scripts/modules/module_block.py | 134 ++++++++++++++++++++++++++++++++++++++++
>   util/module.c                   |  38 ++++--------
>   7 files changed, 227 insertions(+), 31 deletions(-)
>   create mode 100755 scripts/modules/module_block.py
>

 From my point of view the design looks a bit complex.
The approach should be quite similar to one used
in Linux kernel.

If the block driver is configured as a module, block_init
should register proper hooks and create generic lists.
C code parsing does not look like a good approach
to me.

If block_init is a bad name, we could use something like
module_init.