On 2/2/22 16:37, Emanuele Giuseppe Esposito wrote:
So we have disk B with backing file C, and new disk A that wants to have
backing file C.
I think I understand what you mean, so in theory the operation would be
- create new child
- add child to A->children list
- add child to C->parents list
So in theory we need to
* drain A (without subtree), because it can't happen that child nodes of
A have in-flight requests that look at A status (children list), right?
In other words, if A has another node X, can a request in X inspect
A->children
* drain C, as parents can inspect C status (like B). Same assumption
here, C->children[x]->bs cannot have requests inspecting C->parents
list?
In that case (i.e. if parents have to be drained, but children need not)
bdrv_drained_begin_unlocked would be enough, right?
That would mean that ->children is I/O state but ->parents is global
state. I think it's quite a bit more complicated to analyze and to
understand.
Paolo
