Re: [PATCH] cp: use reflink=auto mode by default

[Pádraig Brady]

On 26/06/16 18:07, Alexandru Moise wrote:
> On some filesystems (BTRFS), copying a file within the filesystem may
> cross subvolume boundaries and we can use a lightweight reflink copy,
> which is faster than a full file copy.

Note the above is accurate for mv, but for cp it's significant
for _any_ copy within a BTRFS file system.

> This is enabled by default because it's only an optimization for
> the fall back copy and does not break user expectations or usability.

That simplifies the argument a bit, but I think there is some weight behind 
this change.
Coincidentally? I commented recently at 
https://news.ycombinator.com/item?id=11937781
where I describe there why cp may want to change this default behavior.
However I allude there to an implementation using copy_file_range() to be more
file system agnostic rather than trying something BTRFS specific
and falling back each time.

thanks,
Pádraig