tree bc2c54262cc3d4a777a667fe3089c00cafbf6fd8
parent 0c71550bf36a8d1590486e480fe2deb7253664cb
author Kelvin Zhang <zhangkelvin@google.com> 1612897585 -0500
committer Treehugger Robot <treehugger-gerrit@google.com> 1618898918 +0000

Refactor extent writer to take filedescriptor in constructor

Functions which receive an instance of extent writer need to manually
pass fd to ExtentWriter via Init() call, which breaks separation of
concerns. It makes it hard for us to decouple InstallOp execution from
writing of data, as the execution unit must be aware of which fd to pass
to extent writer. In addition, many extents writer, such as snapshot
extent writer, simply ignores the fd parameter, which is a indication of
poor code structure.

To address the above issue, we pass FileDescriptorPtr via constructor if
needed. This way, whoever is "executing" InstallOps don't need to care
about where the output data is going, and whoever's writing the data
would be responsible for initializing an ExtentWriter.

Test: th
Change-Id: I6d1eabde085eefd55da9ecc0352d4a16ae458698