On Mon, 05/19 13:38, Eric Blake wrote: > On 05/11/2014 07:35 PM, Fam Zheng wrote: > > Dropping intermediate could be useful both for commit and stream, and > > BDS refcnt plus bdrv_swap could do most of the job nicely. It also needs > > to work with op blockers. > > > > Signed-off-by: Fam Zheng <f...@redhat.com> > > --- > > block.c | 139 > > ++++++++++++++++++++++++++++----------------------------- > > block/commit.c | 2 +- > > 2 files changed, 70 insertions(+), 71 deletions(-) > > > > > - > > /* > > - * Drops images above 'base' up to and including 'top', and sets the image > > - * above 'top' to have base as its backing file. > > + * Drops images above 'base' up to and including 'top', and sets new > > 'base' as > > + * backing_hd of top's overlay (the image orignally has 'top' as backing > > file). > > + * top's overlay may be NULL if 'top' is active, no such update needed. > > + * Requires that the top's overlay to 'top' is opened r/w. > > + * > > + * 1) This will convert the following chain: > > + * > > + * ... <- base <- ... <- top <- overlay <-... <- active > > * > > - * Requires that the overlay to 'top' is opened r/w, so that the backing > > file > > - * information in 'bs' can be properly updated. > > + * to > > + * > > + * ... <- base <- overlay <- active > > Jeff is working on allowing the user full control over the string > written into overlay; let's make sure these efforts are coordinated. > https://lists.gnu.org/archive/html/qemu-devel/2014-05/msg02949.html
Looks they are not exclusive functional changes, I can rebase if it is merged before this. > > > + * > > + * 2) It is allowed for bottom==base, in which case it converts: > > * > > - * E.g., this will convert the following chain: > > - * bottom <- base <- intermediate <- top <- active > > + * base <- ... <- top <- overlay <- ... <- active > > * > > * to > > * > > - * bottom <- base <- active > > + * base <- overlay <- active > > * > > - * It is allowed for bottom==base, in which case it converts: > > + * 2) It also allows active==top, in which case it converts: > > Shouldn't this be 3) ? Yes, thanks! > > > * > > - * base <- intermediate <- top <- active > > + * ... <- base <- ... <- top (active) > > * > > * to > > * > > - * base <- active > > + * ... <- base == active == top > > + * > > + * i.e. only base and lower remains: *top == *base when return. > > + * > > + * 3) If base==NULL, it will drop all the BDS below overlay and set its > > and 4) > Yes, thanks! Fam
