Re: Splicing to/from a tty

[Al Viro]

On Wed, Jan 20, 2021 at 10:25:56PM +0000, David Laight wrote:

> I also wonder if pread/pwrite with offset == 0 should be valid
> on things where the offset makes no sense.
> 
> I'm rather surprised the offset isn't just silently ignored
> for devices where seeking is non-sensical.
> You might want to error it for mag tapes, but not pipes,
> ttys, sockets etc.
> 
> I really can't remember what SYSV, Solaris or NetBSD do.

... nor can you be arsed to RTFPOSIX.   Why am I not surprised?

In https://pubs.opengroup.org/onlinepubs/9699919799/functions/write.html
(located by arcane action known as googling for pwrite POSIX):
==============================
The pwrite() function shall fail if:

[EINVAL]
	The file is a regular file or block special file, and the offset argument is negative.
The file offset shall remain unchanged.
[ESPIPE]
	The file is incapable of seeking.
==============================