On Fri, 2 Jun 2023 13:05:14 -0400 Linus Torvalds wrote: > Just to harp some more on this - if SPLICE_F_MORE is seen as purely a > performance hit, with no real semantic value, and will still set > random packet boundaries but we want big packets for all the _usual_ > cases, then I think something like "splice_end()" can be a fine > solution regardless of exact semantics. > > Alternatively, if we make it the rule that "splice_end()" is only > called on EOF situations - so signals etc do not matter - then the > semantics would be stable and sound fine to me too. > > In that second case, I'd like to literally name it that way, and > actually call it "splice_eof()". Because I'd like to really make it > very clear what the semantics would be. > > So a "splice_eof()" sounds fine to me, and we'd make the semantics be > the current behavior: > > - splice() sets SPLICE_F_MORE if 'len > read_len' > > - splice() _clears_ SPLICE_F_MORE if we have hit 'len' > > - splice always sets SPLICE_F_MORE if it was passed by the user > > BUT with the small new 'splice_eof()' rule that: > > - if the user did *not* set SPLICE_F_MORE *and* we didn't hit that > "use all of len" case that cleared SPLICE_F_MORE, *and* we did a > "->splice_in()" that returned EOF (ie zero), *then* we will also do > that ->splice_eof() call. > > The above sounds like "stable and possibly useful semantics" to me. It > would just have to be documented. > > Is that what people want? ->splice_eof() with the proposed semantics sounds perfect for the cases testers complained about it the past, IMHO. We can pencil that in as the contingency plan. Actually I like these semantics so much I'm tempted to ask David to implement it already and save users potential debugging :D > I don't think it's conceptually any different from my suggestion of > saying "->splice_read() can set SPLICE_F_MORE if it has more to give", > just a different implementation that doesn't require changes on the > splice_read() side. Setting SPLICE_F_MORE from the input side does feel much cleaner than guessing in splice.c. But we may end up needing the eof() callback for the corner cases, anyway :(
