On Fri, Sep 27, 2024 at 02:41:39PM -0400, Michael Stone wrote: > On Fri, Sep 27, 2024 at 06:18:20PM +0100, Matthew Wilcox wrote: > > Without looking at the source code, it seems likely that cp blindly > > tries FICLONE without checking to see whether the sparse flag is set. > > I suggest that setting --sparse=always should disable the FICLONE > > optimisation. > > I tend to disagree; the reflink is going to be more efficient in the default > case than making an explicit copy that has holes in it--so why should cp > assume you don't want a reflink? If you want to make an existing file > sparse, just use fallocate -d. Or, you could turn off reflink if you really > want to make a full copy, though this seems strange.
Maybe for cp --sparse=auto that makes sense, but when I've explicitly specified that I want to make a sparse copy, cp is ignoring my instructions. Yes, there are other commands that can make a file sparse, but if cp's current behaviour is correct, then this at least deserves a mention in the manpage because it's confusing as hell.
