Date: Thu, 14 Dec 2000 06:17:40 -0800 From: Julian Elischer <julian@elischer.org> To: Alfred Perlstein <bright@wintelcom.net> Cc: Matt Dillon <dillon@earth.backplane.com>, Kirk McKusick <mckusick@mckusick.com>, arch@FreeBSD.ORG, net@FreeBSD.ORG Subject: Re: patch to cleanup inflight desciptor handling. Message-ID: <3A38D684.F241D6B9@elischer.org> References: <200012131852.KAA17423@beastie.mckusick.com> <200012132106.eBDL6Sg86570@earth.backplane.com> <20001213141917.Q16205@fw.wintelcom.net> <20001213145341.S16205@fw.wintelcom.net>
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Alfred Perlstein wrote: > > * Alfred Perlstein <bright@wintelcom.net> [001213 14:20] wrote: > > * Matt Dillon <dillon@earth.backplane.com> [001213 13:07] wrote: > > > :I believe that your changes have been sorely needed for many > > > :years. While I would like to see regular mbufs given a callback > > > :mechanism, your present approach of using an mbuf cluster > > > :solves 90% of the problem. > > > : > > > : Kirk McKusick > > > > > > ... Aflred, be careful that you don't break things we only just fixed > > > last year. The descriptor passing code has been broken for many years. > > > > > > I think the reason we have to scan the descriptor list is related to > > > locating isolated self-referential 'loops' with descriptor passing and > > > unix domain sockets and closing them. e.g. when you pass a descriptor > > > for a unix-domain socket through a unix-domain socket, it is possible > > > for the socket descriptors to reference each other and thus never have > > > their ref count drop to 0 even when all associated processes have > > > close()'d. This happens all the time. Be sure you don't break the > > > fix that solves that particular problem. > > > > Ok, I'll see if that can happen. Basically since the reference > > never goes to zero on the socket, the buffers are never forced to > > be flushed/cleared and the mbuf will then never be free'd resulting > > it it leaking itself. Basically a socket hanging there with an > > mbuf referencing itself. > > > > I wonder if Linux fixed/has this problem. > > Ok, my patch has this problem: > > void > parent(int con) > { > int fd; > > fd = open("/tmp/wank", O_RDONLY); > send_fd_withdata(con, con, "wank", 4); > sleep (5); > exit(1); > > } > > void > child(int con) > { > int fd, error; > char buf[100]; > > sleep(5); > get_fd_withdata(con, &fd, buf, sizeof(buf)); > send_fd_withdata(con, fd, "foo", 3); > exit(1); > buf[4] = '\0'; > printf("%s\n", buf); > if ((error = read(fd, buf, sizeof(buf))) < 0) > perror("read"); > buf[sizeof(buf)-1] = '\0'; > printf("%s\n", buf); > > > } > > This causes a leak, I think the trick is to just always call sorflush() > when the pcb is free'd. that's what I was trying to point out to you.... It get's more complicate when you have 2 pipes, and each has the filedescriptors for the other one in it. > > Looking at linux they still are using gc. I'll give this a lot > more thought before resubmitting this idea. > > sorry, > -- > -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org] > "I have the heart of a child; I keep it in a jar on my desk." > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-net" in the body of the message -- __--_|\ Julian Elischer / \ julian@elischer.org ( OZ ) World tour 2000 ---> X_.---._/ presently in: Budapest v To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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