On Fri, Sep 27, 2024 at 09:31:37PM +0100, Matthew Wilcox wrote:
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.
It would be just as confusing for cp to ignore reflink, right?
