Hi, all
currently I find that when do copy on write for a clone image. librbd
call the cls copyup function to write the data, reading from its
parent, to the child.
However, there is a issue here: if an object in the parent image -->
[0, 8192] with data and [8192, end] without data, then after COW
operation, it will filling the whole object [0, end] to the children
object with [8192, end] all zeros. This phenomenon also occurs in
flatten images.
Actually, we already have sparse_read to just read data without holes.
However, copyup function does not support to write serveral fragments
such as {[0, 8192], [16384,20480]}.
So it that possible to direct send OSDOp {[cow write], [cow write],
[user write]} instead of OSDOp {[copyup], [user write]} ?
Regards
Ning Yao
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