Subject: cp fails for files > 2 GB if copy offload is unsupported

From: Sam James <[email-masked]>
Date: Fri, 02 Jun 2023 16:44:57 +0100

Hello,

Forwarding a downstream report of a behaviour change between
coreutils-9.1 and coreutils-9.3 from https://bugs.gentoo.org/907474.

The reporter bisected it to 093a8b4bfaba60005f14493ce7ef11ed665a0176
("copy: fix --reflink=auto to fallback in more cases", see bug#62404)
and gave strace output showing:
```
fadvise64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0
copy_file_range(3, NULL, 4, NULL, 9223372035781033984, 0) = 2147479552
copy_file_range(3, NULL, 4, NULL, 9223372035781033984, 0) = -1 EINVAL
(Invalid argument)
```

"""
When I try to copy a large file (> 2 GB) like so:

cp --debug file_a file_b

output looks like this:

'file_a' -> 'file_b'
cp: error copying 'file_a' to 'file_b': Invalid argument
copy offload: unsupported, reflink: unsupported, sparse detection: no

Afterwards file_b has a size of 2147479552 bytes (= 2G - 4K).

On another system (with newer kernel version) it looks like this:

cp --debug file_a file_b
'file_a' -> 'file_b'
copy offload: yes, reflink: unsupported, sparse detection: no
"""

Let me know if you need further information, although there's
some more on the downstream Gentoo bug I linked.

Apparently this is only happening w/ the 4.19.x kernels.

Thanks!