On Tue 01-10-13 12:58:17, Zach Brown wrote: > > - app calls splice(from, 0, to, 0, SIZE_MAX) > > 1) VFS calls ->direct_splice(from, 0, to, 0, SIZE_MAX) > > 1.a) fs reflinks the whole file in a jiffy and returns the size of the file > > 1 b) fs does copy offload of, say, 64MB and returns 64M > > 2) VFS does page copy of, say, 1MB and returns 1MB > > - app calls splice(from, X, to, X, SIZE_MAX) where X is the new offset > > (It's not SIZE_MAX. It's MAX_RW_COUNT. INT_MAX with some > PAGE_CACHE_SIZE rounding noise. For fear of weird corners of fs code > paths that still use int, one assumes.) > > > The point is: the app is always doing the same (incrementing offset > > with the return value from splice) and the kernel can decide what is > > the best size it can service within a single uninterruptible syscall. > > > > Wouldn't that work? > > It seems like it should, if people are willing to allow splice() to > return partial counts. Quite a lot of IO syscalls technically do return > partial counts today if you try to write > MAX_RW_COUNT :). Yes. Also POSIX says that application must handle such case for read & write. But in practice programmers are lazy. > But returning partial counts on the order of a handful of megs that the > file systems make up as the point of diminishing returns is another > thing entirely. I can imagine people being anxious about that. > > I guess we'll find out! Return 4 KB once in a while to screw up buggy applications from the start :-p Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
