On Mon, May 24 2010, OGAWA Hirofumi wrote: > Jens Axboe <jens.axboe@xxxxxxxxxx> writes: > > >> > We can easily make F_GETPIPE_SZ return bytes, but I don't think passing > >> > in bytes to F_SETPIPE_SZ makes a lot of sense. The pipe array must be a > >> > power of 2 in pages. So the question is if that makes the API cleaner, > >> > passing in number of pages but returning bytes? Or pass in bytes all > >> > around, but have F_SETPIPE_SZ round to the nearest multiple of pow2 in > >> > pages if need be. Then it would return a size at least what was passed > >> > in, or error. > > I really think "power of 2 in pages" is simply current implementation > detail, not detail of pipe API. Completely agree, one more reason more to make that dependency exposed in the API. > >> I'd recommend this: Pass it in and out in bytes. Don't round to a > >> power of 2. Require the user to know what they are doing. Give an > >> error if the user doesn't supply a power-of-2 * page-size for > >> F_SETPIPE_SZ. (Again, consider the case of architectures with > >> switchable page sizes.) > > > > But is there much point in erroring on an incorrect size? If the > > application says "I need at least 120kb of space in there", kernel > > returns "OK, you got 128kb". Would returning -1/EINVAL for that case > > really make a better API? Doesn't seem like it to me. > > FWIW, my first impression of this was setsockopt(SO_RCV/SNDBUF) of unix > socket. Well, API itself wouldn't say "at least this size" or "exactly > this size", so, in here, important thing is consistency of interfaces, I > think. (And the both is sane API at least for me if those had > consistency in the system.) > > Well, so how about set/get in bytes, and kernel will set "at least > specified size" actually like setsockopt(SO_RCV/SNDBUF)? Isn't that pretty much what I described? -- Jens Axboe -- 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
