copy on write for splice() from file to pipe?

[Stefan Metzmacher]

Am 10.02.23 um 19:19 schrieb Jeremy Allison:
> On Fri, Feb 10, 2023 at 09:57:20AM -0800, Andy Lutomirski via samba-technical wrote:
>>
>> (And if Samba needs to make sure that future writes don't change the
>> outgoing data even two seconds later when the data has been sent but
>> not acked, then maybe a fancy API could be added to help, or maybe
>> Samba shouldn't be using zero copy IO in the first place!)
> 
> Samba doesn't need any of this. The simplest thing to do is
> to restrict splice-based zero-copy IO to files leased by
> a single client, where exclusive access to changes is controled
> by the client redirector.

Yes, I guess we can use it if the file is read-only (from it's acls),
or when the client has a read lease. And of course we can have an I don't care
option, maybe reusing 'use sendfile = yes' as that has the same problem in
the existing code already.

metze