Re: [PATCH] copy: disallow copy_file_range() on Linux kernels before 5.3

[Pádraig Brady]

On 18/05/2021 19:47, Kaz Kylheku (Coreutils) wrote:
> On 2021-05-12 16:09, Pádraig Brady wrote:
> > copy_file_range() before Linux kernel release 5.3 had many issues,
>
> Remark: although there is nothing wrong with the patch, and it is
> necessary, this seems like an issue for the C library to handle,
> as well.
>
> - The GNU C library provides the function copy_file_range. The
>     fact that this is a linux kernel feature is abstracted by the library.
>
> - The GNU C library knows what version of the kernel it is running on,
>     and provides workarounds in relation to that (or possibly refuses
>     to run at all).
>
> So, arguably, the responsibility of somehow working around this lies
> with glibc; glibc is the purveyor of the API.
>
> Unfortunately, I don't see any discussions about the issue in
> libc-alpha mailing list.
>
> The situation is not acceptable that a GNU program is working around
> broken GNU library functions, with no action being taken in the
> GNU library (even if that program will need to carry those workarounds
> anyway).

There is some validity to handling this in glibc.
However it would also have to be handled in musl libc etc. to be able to rely 
on that.
Also some uses of copy_file_range() might have been ok,
so precluding all uses may have been too restrictive.
Only a general copy program like cp needs to be careful as to use.
BTW I think Centos 7 disabled this at the glibc level due to general brokenness.

cheers,
Pádraig