bug#63850: cp fails for files > 2 GB if copy offload is unsupported

[Mike Gilbert]

On Fri, Jun 02, 2023 at 11:05:24PM -0700, Paul Eggert wrote:
> On 2023-06-02 09:31, Pádraig Brady wrote:
> > I'm not sure it was working correctly before 9.3 either.
> > Before 9.3 we would have switched from copy_file_range() to read()/write()
> 
> Actually, cp shouldn't have been using copy_file_range at all, as the 
> code is supposed to never use copy_file_range unless the Linux kernel 
> version is 5.3 or later. See m4/copy-file-range.m4 and 
> lib/copy-file-range.c.
> 
> Since the bug is being reported against kernel 4.19, someone needs to 
> investigate why the Gentoo build is using the copy_file_range syscall on 
> that kernel. Either the Gentoo build isn't properly compiling the 
> replacement function in coreutils/lib/copy-file-range.c, or the 
> replacement function is incorrectly deciding that the kernel is new 
> enough, or something like that.
> 
> We shouldn't need to fiddle with src/copy.c on this.

The macro in copy-file-range.m4 performs a build time version check
against the installed linux headers (/usr/include/linux).

In this case, headers from linux-6.1 are being used at build time.
However, the code is being run on a linux-4.19 kernel.

Generally speaking, syscall checks must be done at run time on Linux,
not build time.