* Unify sparse and normal IO output
This commit refactors the code paths that excercise normal and sparse
writing of restored content. The goal is to expose sparsefile.Copy()
and iocopy.Copy() to be interchangeable, thereby allowing us to wrap
or transform their behavior more easily in the future.
* Introduce getStreamCopier()
* Pull ioCopy() into getStreamCopier()
* Fix small nit in E2E test
We should be getting the block size of the destination file, not
the source file.
* Call stat.GetBlockSize() once per FilesystemOutput
A tiny refactor to pull this call out of the generated stream copier,
as the block size should not change from one file to the next within
a restore entry.
NOTE: as a side effect, if block size could not be found (an error
is returned), we will return the default stream copier instead of
letting the sparse copier fail. A warning will be logged, but this
error will not cause the restore to fail; it will proceed silently.
* feat(snapshots): support restoring sparse files
This commit implements basic support for restoring sparse files from
a snapshot. When specifying "--mode=sparse" in a snapshot restore
command, Kopia will make a best effort to make sure the underlying
filesystem allocates the minimum amount of blocks needed to persist
restored files. In other words, enabling this feature will "force"
all restored files to be sparse-blocks of zero bytes in the source
file should not be allocated.
* Address review comments
- Separate sparse option into its own bool flag
- Implement sparsefile packagewith copySparse method
- Truncate once before writing sparse file
- Check error from Truncate
- Add unit test for copySparse
- Invoke GetBlockSize once per file copy
- Remove support for Windows and explain why
- Add unit test for stat package
Co-authored-by: Dave Smith-Uchida <dave@kasten.io>
