feat: Add reflink FileCopyMethod (copy-on-write) #166
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This will be used so we can have multiple implementations for copying a regular file. Currently, there is just CopyBytes, which is the old fcopy code. The FileCopyMethod struct is a struct with an un-exported member. This is done to make the type opaque so the user can't make their own copy function. There are still design questions left about passing around the `Options` struct and `os.FileInfo`, so I opted to do this so that can be figured out later. The type can be made into `type FileCopyMethod func(...)` later, and it won't be a breaking change. Or, instead, a `UserCopy(func (src, dest string) error) FileCopyMethod` function can be added.
Permission changes, ownership preservation, and access/modify/creation time presevation is something all implementations need. I brought it out of the CopyBytes implementation so it can be shared when more implementations are added later. A small note: The "ignore if source file deleted" check had to be brought out of `CopyBytes`. The way it worked before is it returned no error, which meant `fcopy` would try and modify the destination file (which was never created). Instead, I check for the error explicitly in `fcopy`.
External contributors don't do development on the main or develop branch, but may still need to see the CI results. This lets them do `gh workflow run Go --repo=<user>/copy` on their own branches.
When we add support for reflinks, we need to make sure we are able to check that regressions aren't introduced. Explicitly testing on different filesystems allows us to do that.
We want comprehensive testing, no matter the FileCopyMethod. Using an environment variable is a quick, clean, and easy way to do this.
The only `FileCopyMethod` that supports this is CopyBytes.
The only `FileCopyMethod` that supports this is CopyBytes.
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This commit is stacked on top of #165. That must be reviewed and merged first.
Note
I'm calling it
reflinkbecause that's what Linux users understand it as.This brings copy-on-write file copying support as a
FileCopyMethod.Tests are passing: https://github.com/eth-p/forked-copy/actions/runs/10543146003/
TODO