Nick, Jens On Tue, Aug 5, 2008 at 4:57 AM, Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote: > On Tuesday 05 August 2008 01:29, Jamie Lokier wrote: >> Nick Piggin wrote: >> > On Saturday 02 August 2008 04:28, Miklos Szeredi wrote: >> > > On Fri, 1 Aug 2008, Nick Piggin wrote: >> > > > Well, a) it probably makes sense in that case to provide another mode >> > > > of operation which fills the data synchronously from the sender and >> > > > copys it to the pipe (although the sender might just use read/write) >> > > > And b) we could *also* look at clearing PG_uptodate as an >> > > > optimisation iff that is found to help. >> > > >> > > IMO it's not worth it to complicate the API just for the sake of >> > > correctness in the so-very-rare read error case. Users of the splice >> > > API will simply ignore this requirement, because things will work fine >> > > on ext3 and friends, and will break only rarely on NFS and FUSE. >> > > >> > > So I think it's much better to make the API simple: invalid pages are >> > > OK, and for I/O errors we return -EIO on the pipe. It's not 100% >> > > correct, but all in all it will result in less buggy programs. >> > >> > That's true, but I hate how we always (in the VM, at least) just brush >> > error handling under the carpet because it is too hard :( >> > >> > I guess your patch is OK, though. I don't see any reasons it could cause >> > problems... >> >> At least, if there are situations where the data received is not what >> a common sense programmer would expect (e.g. blocks of zeros, data >> from an unexpected time in syscall sequence, or something, or just >> "reliable except with FUSE and NFS"), please ensure it's documented in >> splice.txt or wherever. > > Not quite true. Many filesystems can return -EIO, and truncate can > partially zero pages. > > Basically the man page should note that until the splice API is > improved, then a) -EIO errors will be seen at the receiever, b) > the pages can see transient zeroes (this is the case with read(2) > as well, but splice has a much bigger window), and c) the sender > does not send a snapshot of data because it can still be modified > until it is recieved. > > c is not too surprising for an asynchronous interface, but it is > nice to document in case people are expecting COw or something. > b and c can more or less be worked around by not doing silly things > like truncating or scribbling on data until reciever really has it. > a, I argue, should be fixed in API. Nick, could you come up with a patch to the man page for this? Something that's ACKable by Jens? Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
