Messages in this thread | | | Date | Fri, 3 Jul 2009 16:27:29 +0800 | Subject | Re: PROPOSAL: extend pipe() to support NULL argument. | From | Changli Gao <> |
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On Fri, Jul 3, 2009 at 4:16 PM, Amerigo Wang<xiyou.wangcong@gmail.com> wrote: > On Fri, Jul 03, 2009 at 03:40:34PM +0800, Changli Gao wrote: >>On Fri, Jul 3, 2009 at 3:15 PM, Amerigo Wang<xiyou.wangcong@gmail.com> wrote: >>> >>> If saving one fd really helps here, probably you want to >>> save more, you will need a syscall like: >>> >>> int splice_without_new_fd(int infd, int outfd); >>Do you know sendfile()? Its current implementation is buggy, and will >>be blocked on outfd. Anyway, the above code is just a use case, there >>are other cases sendfile can't cover. > > So what? So you should fix it intead of inventing a new pipe() and use > splice(2)... I said: It just a special case. Fixing sendfile() won't fix everything.
> > Wait... if splice(2) doesn't block, what is your point for saving > an fd in your code? You can do: > > int splice_two_fd(int fd1, int fd2) > { > int fds[2]; > pipe(fds); > splice(fd1, fds[0]);//not block > splice(fds[1], fd2);//not block > close(fds[0]); //can be closed soon > close(fds[1]); //ditto > } > > Outside this function no new fd's are used. > In fact, sendfile(2) is implemented via splice(2) infrastructure. The logic is the same, and much clever than yours. Dive into its code, you will find the reason why it must be blocked on outfd.
>> >>> >>> But splice(2) is designed to be as it is. You need to increase >>> your fd limit, instead of saving one by pipe(). >>> >>I don't agree with you. We should save resource as much as we can, and >>not work around it. > > You are saying splice(2) is wrong? Because it is splice(2) who > needs 3 fd's finally. > It isn't splice(2)'s fault. In fact, I can also work around this issue by named pipe.
-- Regards, Changli Gao(xiaosuo@gmail.com) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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