On 16.01.20 17:00, Richard W.M. Jones wrote: > On Thu, Jan 16, 2020 at 05:38:03PM +0200, Maxim Levitsky wrote: >> How about doing write zeros without discard only in this particular case >> (convert to existing image) >> Basically omitting the BDRV_REQ_MAY_UNMAP flag to blk_co_pwrite_zeroes. >> It will be slow, but maybe for this particular case, it is acceptable? > > I should probably say that we don't want to break the other case > (which is likely more important) where we write a sparse source to a > sparse target and want the target to contain only the union of the two > sparse maps, not fully allocated :-) > > It would be fine, I think, to have a new "make this disk fully > allocated" operation. qemu-img resize could almost do it with a > request to add 0 extra bytes, but the --preallocation flag only > applies to the new space.
Well, that works with -S 0, as Kevin has said. But that will take time because it will write actual zeroes wherever the source is zero. Max
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