On Mon, May 24, 2010 at 9:04 AM, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > 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? Actually, SO_*BUF is pretty weird. It returns double what was supplied. It's not simply a matter of rounding up: it always doubles what was supplied. -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface" http://blog.man7.org/ -- 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
