Ping On 13.07.18 13:14, Max Reitz wrote: > This series allows using qemu-img rebase on images that do not have a > backing file. Right now, this fails with the rather cryptic error > message: > > $ qemu-img rebase -b base.qcow2 foo.qcow2 > qemu-img: Could not open old backing file '': The 'file' block driver > requires a file name > > Yeah, well, OK. > > With how rebase currently works, this would lead to the overlay being > filled with zeroes, however. This is where patch 2 comes in and instead > makes rebase use blk_pwrite_zeroes() whenever it handles an area past > the input’s backing file’s EOF. > > (Note that additionally we could try to punch holes in the overlay > whenever it matches the new backing file, but that’s something I’ll put > off for later. (We don’t even have a reliable method for punching holes > into an overlay yet, although I would like to have such because it could > make active commit more efficient.)) > > > And patch 3 adds the usual test. > > > Max Reitz (3): > qemu-img: Allow rebase with no input base > qemu-img: Use zero writes after source backing EOF > iotests: Add test for rebase without input base > > qemu-img.c | 72 +++++++++++++++++++++++--------------- > tests/qemu-iotests/024 | 70 ++++++++++++++++++++++++++++++++++++ > tests/qemu-iotests/024.out | 37 ++++++++++++++++++++ > 3 files changed, 150 insertions(+), 29 deletions(-) >
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