On Wed, 17 Sep 2014 22:20:45 +0000 Milosz Tanski <milosz@xxxxxxxxx> wrote: > This patcheset introduces an ability to perform a non-blocking read from > regular files in buffered IO mode. This works by only for those filesystems > that have data in the page cache. > > It does this by introducing new syscalls new syscalls readv2/writev2 and > preadv2/pwritev2. These new syscalls behave like the network sendmsg, recvmsg > syscalls that accept an extra flag argument (O_NONBLOCK). So I'm trying to understand the reasoning behind this approach so I can explain it to others. When you decided to add these syscalls, you ruled out some other approaches that have been out there for a while. I assume that, before these syscalls can be merged, people will want to understand why you did that. So I'll ask the dumb questions: - Non-blocking I/O has long been supported with a well-understood set of operations - O_NONBLOCK and fcntl(). Why do we need a different mechanism here - one that's only understood in the context of buffered file I/O? I assume you didn't want to implement support for poll() and all that, but is that a good enough reason to add a new Linux-specific non-blocking I/O technique? - Patches adding fincore() have been around since at least 2010; see, for example, https://lwn.net/Articles/371538/ or https://lwn.net/Articles/604640/. It seems this could be used in favor of four new read() syscalls; is there a reason it's not suitable for your use case? - Patches adding buffered support for AIO have been around since at least 2003 - https://lwn.net/Articles/24422/, for example. I guess I don't really have to ask why you don't want to take that approach! :) Apologies for my ignorance here; that's what I get for hanging around with the MM folks at LSFMM, I guess. Anyway, I suspect I'm not the only one who would appreciate any background you could give here. Thanks, jon -- 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
