Hi:
I am reading the code of overlayfs and have some questions about copy-up.
If a file which doesn't exist on upper directory is modified, this file will
be copied to work directory and then be renamed to upper directory.
1. It seems the whole file(in lower directory) will be copied, that will be
a big cost in time and space. Is there any way to just copy the
modifed part?
Like "cp --reflink", keep the modified part in upper directory?
2. What's the purpose of renaming a file from work directory to upper directory?
Because rename is atomic?
3. When you talk about "a persistent file handle", what's the exact
form of "file handle",
is it "struct file * file"?
My questions may be silly, I would appreciate it if you could give me
a bit of hint.
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