Re: [Qemu-devel] [PATCHv3] block-migration: efficiently encode zero blocks

[Peter Lieven]

On 18.07.2013 07:03, Stefan Hajnoczi wrote:
> On Mon, Jul 15, 2013 at 12:55:05PM +0200, Peter Lieven wrote:
> > @@ -114,16 +115,29 @@ static void blk_mig_unlock(void)
> >   static void blk_send(QEMUFile *f, BlkMigBlock * blk)
> >   {
> >       int len;
> > +    uint64_t flags = BLK_MIG_FLAG_DEVICE_BLOCK;
> > +
> > +    if (migrate_zero_blocks() && buffer_is_zero(blk->buf, BLOCK_SIZE)) {
> [...]
> > +bool migrate_zero_blocks(void)
> > +{
> > +    MigrationState *s;
> > +
> > +    s = migrate_get_current();
> > +
> > +    return s->enabled_capabilities[MIGRATION_CAPABILITY_ZERO_BLOCKS];
> > +}
> blk_send() is called without locks held.  It would be safer and cleaner
> to stash bool migrate_zero_blocks in BlkMigBlock in init_blk_migration()
> instead of accessing migrate_get_current() without locks held.
>
> This eliminates the assumption that accessing migrate_get_current() is
> safe without locks.
>
> Besides this locking issue I'm happy with the code.
Thank you,

I will sent a v4 shortly. I have to rebase it anyway.

Peter