On Sat, Sep 28, 2024 at 01:20:17AM +0100, Matthew Wilcox wrote:
On Fri, Sep 27, 2024 at 06:23:05PM -0400, Michael Stone wrote:
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?
I didn't ask cp to use reflink. It chose to do that all by itself.
I asked for a sparse file to be made, and it didn't do that.
You did, by not selecting reflink=always or reflink=never.
