linux-kernel - Re: PROPOSAL: extend pipe() to support NULL argument.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 3 Jul 2009 16:27:29 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Amerigo Wang <xiyou.wangcong@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: PROPOSAL: extend pipe() to support NULL argument.

On Fri, Jul 3, 2009 at 4:16 PM, Amerigo Wang<xiyou.wangcong@...il.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@...il.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@...il.com)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/