Re: [Qemu-devel] [PATCH] block migration: Allow compile time disable

[Kashyap Chamarthy <kchamart@redhat.com>]

On Wed, May 03, 2017 at 11:42:57AM +0100, Dr. David Alan Gilbert (git) wrote:

A small comment inline, in the 'ifndef' section.

> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Many users now prefer to use drive_mirror over NBD as an
> alternative to the older migrate -b option; drive_mirror is
> more complex to setup but gives you more options (e.g. only
> migrating some of the disks if some of them are shared).
> 
> Allow the large chunk of block migration code to be compiled
> out for those who don't use it.
> 
> Based on a downstream-patch we've had for a while by Jeff Cody.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  configure               | 11 +++++++++++
>  migration/Makefile.objs |  2 +-
>  migration/migration.c   | 12 ++++++++++++
>  vl.c                    |  2 ++
>  4 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/configure b/configure
> index 48a9370cc6..69eed5fb8d 100755
> --- a/configure
> +++ b/configure
> @@ -316,6 +316,7 @@ vte=""
>  virglrenderer=""
>  tpm="yes"
>  libssh2=""
> +live_block_migration="yes"
>  numa=""
>  tcmalloc="no"
>  jemalloc="no"
> @@ -1168,6 +1169,10 @@ for opt do
>    ;;
>    --enable-libssh2) libssh2="yes"
>    ;;
> +  --disable-live-block-migration) live_block_migration="no"
> +  ;;
> +  --enable-live-block-migration) live_block_migration="yes"
> +  ;;
>    --disable-numa) numa="no"
>    ;;
>    --enable-numa) numa="yes"
> @@ -1400,6 +1405,7 @@ disabled with --disable-FEATURE, default is enabled if available:
>    libnfs          nfs support
>    smartcard       smartcard support (libcacard)
>    libusb          libusb (for usb passthrough)
> +  live-block-migration   Block migration in the main migration stream
>    usb-redir       usb network redirection support
>    lzo             support of lzo compression library
>    snappy          support of snappy compression library
> @@ -5210,6 +5216,7 @@ echo "TPM support       $tpm"
>  echo "libssh2 support   $libssh2"
>  echo "TPM passthrough   $tpm_passthrough"
>  echo "QOM debugging     $qom_cast_debug"
> +echo "Live block migration $live_block_migration"
>  echo "lzo support       $lzo"
>  echo "snappy support    $snappy"
>  echo "bzip2 support     $bzip2"
> @@ -5776,6 +5783,10 @@ if test "$libssh2" = "yes" ; then
>    echo "LIBSSH2_LIBS=$libssh2_libs" >> $config_host_mak
>  fi
>  
> +if test "$live_block_migration" = "yes" ; then
> +  echo "CONFIG_LIVE_BLOCK_MIGRATION=y" >> $config_host_mak
> +fi
> +
>  # USB host support
>  if test "$libusb" = "yes"; then
>    echo "HOST_USB=libusb legacy" >> $config_host_mak
> diff --git a/migration/Makefile.objs b/migration/Makefile.objs
> index 480dd493a9..200b5e0c67 100644
> --- a/migration/Makefile.objs
> +++ b/migration/Makefile.objs
> @@ -9,5 +9,5 @@ common-obj-y += qjson.o
>  
>  common-obj-$(CONFIG_RDMA) += rdma.o
>  
> -common-obj-y += block.o
> +common-obj-$(CONFIG_LIVE_BLOCK_MIGRATION) += block.o
>  
> diff --git a/migration/migration.c b/migration/migration.c
> index 353f2728cf..ffce72aabc 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -692,6 +692,7 @@ MigrationInfo *qmp_query_migrate(Error **errp)
>  
>          populate_ram_info(info, s);
>  
> +#ifdef CONFIG_LIVE_BLOCK_MIGRATION
>          if (blk_mig_active()) {
>              info->has_disk = true;
>              info->disk = g_malloc0(sizeof(*info->disk));
> @@ -699,6 +700,7 @@ MigrationInfo *qmp_query_migrate(Error **errp)
>              info->disk->remaining = blk_mig_bytes_remaining();
>              info->disk->total = blk_mig_bytes_total();
>          }
> +#endif
>  
>          if (cpu_throttle_active()) {
>              info->has_cpu_throttle_percentage = true;
> @@ -720,6 +722,7 @@ MigrationInfo *qmp_query_migrate(Error **errp)
>  
>          populate_ram_info(info, s);
>  
> +#ifdef CONFIG_LIVE_BLOCK_MIGRATION
>          if (blk_mig_active()) {
>              info->has_disk = true;
>              info->disk = g_malloc0(sizeof(*info->disk));
> @@ -727,6 +730,7 @@ MigrationInfo *qmp_query_migrate(Error **errp)
>              info->disk->remaining = blk_mig_bytes_remaining();
>              info->disk->total = blk_mig_bytes_total();
>          }
> +#endif
>  
>          get_xbzrle_cache_stats(info);
>          break;
> @@ -1222,6 +1226,14 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
>      params.blk = has_blk && blk;
>      params.shared = has_inc && inc;
>  
> +#ifndef CONFIG_LIVE_BLOCK_MIGRATION
> +    if (params.blk || params.shared) {
> +        error_setg(errp, "QEMU compiled without old-style block migration. "
> +                         "Use drive_mirror+NBD.");

Is it worth spelling out briefly what the "old-style block migration"
is?  Something like:

    "QEMU compiled without old-style (i.e. QMP `migrate` with
    "inc":true) block migration. Use `drive-mirror`+NBD")
 
But I also wonder if it's needlessly wordy, so your call to incorporate
it or not.

I spelled out the QMP equivalent (as opposed to HMP: 'migrate -b')
because, that's what users of higher layers (libvirt, OpenStack etc) see
in their QMP interactions with QEMU, when the old-style approach is
used:

    {"execute":"migrate","arguments":{{"detach":true,"blk":false,"inc":true,"uri":"fd:migrate"}


[...]

-- 
/kashyap