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Date: Sat, 12 Sep 2020 00:43:27 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Alan Somers <asomers@freebsd.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: Re: svn commit: r365643 - head/bin/cp
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On Fri, Sep 11, 2020 at 08:49:36PM +0000, Alan Somers wrote:
> Author: asomers
> Date: Fri Sep 11 20:49:36 2020
> New Revision: 365643
> URL: https://svnweb.freebsd.org/changeset/base/365643
> 
> Log:
>   cp: fall back to read/write if copy_file_range fails
>   
>   Even though copy_file_range has a file-system agnostic version, it still
>   fails on devfs (perhaps because the file descriptor is non-seekable?) In
>   that case, fallback to old-fashioned read/write. Fixes
>   "cp /dev/null /tmp/null"

Devices are seekable.

The reason for EINVAL is that vn_copy_file_range() checks that both in and out
vnodes are VREG.  For devfs, they are VCHR.