Re: [Qemu-devel] [PATCH v2 10/17] block: define get_block_status return value

[Peter Lieven]

On 19.07.2013 11:58, Paolo Bonzini wrote:
> Il 19/07/2013 08:48, Peter Lieven ha scritto:
> > > -    return bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
> > > +    int64_t ret = bdrv_get_block_status(bs, sector_num, nb_sectors,
> > > pnum);
> > > +    return
> > > +        (ret & BDRV_BLOCK_DATA) ||
> > > +        ((ret & BDRV_BLOCK_ZERO) && !bdrv_has_zero_init(bs));
> > i do also not understand the "((ret & BDRV_BLOCK_ZERO) &&
> > !bdrv_has_zero_init(bs))";
> > if a block is unallocated and reads as zero, but the device lacks zero
> > init, it is declared as allocated with this, isn't it?
> Thinking more about it, I would say it is a bugfix.
>
> If a block is unallocated and reads as zero, but the device lacks zero
> init, the block contents have changed since the guest was created.  Thus
> the guest might well be relying on the zero content of the block, and it
> should be treated as allocated.
i was told that has_zero_init sole task is to report the state
of the device right after iscsi_create(). using it for r/w in qemu
might be a misuse.

> In any case, better safe than sorry---if in doubt, the conservative
> answer is always to return 1, and callers who want more precise
> information can use bdrv_get_block_status.
you mean for every call to the deprecated bdrv_is_allocate()?

Peter