Am 06.01.2012 15:01, schrieb Stefan Hajnoczi: > From: Marcelo Tosatti <mtosa...@redhat.com> > > Add support for streaming data from an intermediate section of the > image chain (see patch and documentation for details). > > Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> > --- > block.c | 64 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > block.h | 4 +++ > block/stream.c | 28 +++++++++++++++++++++--- > block_int.h | 3 +- > blockdev.c | 11 ++++++--- > 5 files changed, 101 insertions(+), 9 deletions(-) > > diff --git a/block.c b/block.c > index 9b688a0..d2143b1 100644 > --- a/block.c > +++ b/block.c > @@ -2263,6 +2263,70 @@ int bdrv_is_allocated(BlockDriverState *bs, int64_t > sector_num, int nb_sectors, > return data.ret; > } > > +/* > + * Given an image chain: [BASE] -> [INTER1] -> [INTER2] -> [TOP] > + * > + * Return true if the given sector is allocated in top or base. > + * Return false if the given sector is allocated in intermediate images.
This description is inexact. A sector could be allocated both in base in an intermediate image. Also initially I thought that we not only need to check whether the sector is allocated in BASE, but also in any parents of BASE. You don't do this: Clusters that are completely unallocated all through the chain are reported as allocated. After reading all of the patch, I believe this provides the right semantics: "Normal" image streaming would copy them into the topmost file, but if you keep a backing file, you want to copy as little as possible and keep using the backing file whenever possible. So I suggest to fix the description rather than the implementation. Maybe we should also rename the function. With this semantics it's not a generic is_allocated function any more, but something quite specific to streaming with a base file. Kevin
