Re: [Qemu-devel] [PATCH v2 1/4] Add basic version of bridge helper

[Blue Swirl]

On Fri, Oct 21, 2011 at 15:07, Corey Bryant <address@hidden> wrote:
> This patch adds a helper that can be used to create a tap device attached to
> a bridge device.  Since this helper is minimal in what it does, it can be
> given CAP_NET_ADMIN which allows qemu to avoid running as root while still
> satisfying the majority of what users tend to want to do with tap devices.
>
> The way this all works is that qemu launches this helper passing a bridge
> name and the name of an inherited file descriptor.  The descriptor is one
> end of a socketpair() of domain sockets.  This domain socket is used to
> transmit a file descriptor of the opened tap device from the helper to qemu.
>
> The helper can then exit and let qemu use the tap device.
>
> Signed-off-by: Anthony Liguori <address@hidden>
> Signed-off-by: Richa Marwaha <address@hidden>
> Signed-off-by: Corey Bryant <address@hidden>
> ---
>  Makefile             |   12 +++-
>  configure            |    1 +
>  qemu-bridge-helper.c |  205 
> ++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 216 insertions(+), 2 deletions(-)
>  create mode 100644 qemu-bridge-helper.c
>
> diff --git a/Makefile b/Makefile
> index f63fc02..d9b447e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -35,6 +35,8 @@ $(call set-vpath, $(SRC_PATH):$(SRC_PATH)/hw)
>
>  LIBS+=-lz $(LIBS_TOOLS)
>
> +HELPERS-$(CONFIG_LINUX) = qemu-bridge-helper$(EXESUF)
> +
>  ifdef BUILD_DOCS
>  DOCS=qemu-doc.html qemu-tech.html qemu.1 qemu-img.1 qemu-nbd.8 
> QMP/qmp-commands.txt
>  else
> @@ -75,7 +77,7 @@ defconfig:
>
>  -include config-all-devices.mak
>
> -build-all: $(DOCS) $(TOOLS) recurse-all
> +build-all: $(DOCS) $(TOOLS) $(HELPERS-y) recurse-all
>
>  config-host.h: config-host.h-timestamp
>  config-host.h-timestamp: config-host.mak
> @@ -153,6 +155,8 @@ qemu-img$(EXESUF): qemu-img.o $(tools-obj-y)
>  qemu-nbd$(EXESUF): qemu-nbd.o $(tools-obj-y)
>  qemu-io$(EXESUF): qemu-io.o cmd.o $(tools-obj-y)
>
> +qemu-bridge-helper$(EXESUF): qemu-bridge-helper.o
> +
>  qemu-img-cmds.h: $(SRC_PATH)/qemu-img-cmds.hx
>        $(call quiet-command,sh $(SRC_PATH)/scripts/hxtool -h < $< > $@,"  GEN 
>   $@")
>
> @@ -221,7 +225,7 @@ clean:
>  # avoid old build problems by removing potentially incorrect old files
>        rm -f config.mak op-i386.h opc-i386.h gen-op-i386.h op-arm.h opc-arm.h 
> gen-op-arm.h
>        rm -f qemu-options.def
> -       rm -f *.o *.d *.a *.lo $(TOOLS) qemu-ga TAGS cscope.* *.pod *~ */*~
> +       rm -f *.o *.d *.a *.lo $(TOOLS) $(HELPERS-y) qemu-ga TAGS cscope.* 
> *.pod *~ */*~
>        rm -Rf .libs
>        rm -f slirp/*.o slirp/*.d audio/*.o audio/*.d block/*.o block/*.d 
> net/*.o net/*.d fsdev/*.o fsdev/*.d ui/*.o ui/*.d qapi/*.o qapi/*.d qga/*.o 
> qga/*.d
>        rm -f qemu-img-cmds.h
> @@ -289,6 +293,10 @@ install: all $(if $(BUILD_DOCS),install-doc) 
> install-sysconfig
>  ifneq ($(TOOLS),)
>        $(INSTALL_PROG) $(STRIP_OPT) $(TOOLS) "$(DESTDIR)$(bindir)"
>  endif
> +ifneq ($(HELPERS-y),)
> +       $(INSTALL_DIR) "$(DESTDIR)$(libexecdir)"
> +       $(INSTALL_PROG) $(STRIP_OPT) $(HELPERS-y) "$(DESTDIR)$(libexecdir)"
> +endif
>  ifneq ($(BLOBS),)
>        $(INSTALL_DIR) "$(DESTDIR)$(datadir)"
>        set -e; for x in $(BLOBS); do \
> diff --git a/configure b/configure
> index 4f87e0a..6c8b659 100755
> --- a/configure
> +++ b/configure
> @@ -2768,6 +2768,7 @@ echo "datadir=$datadir" >> $config_host_mak
>  echo "sysconfdir=$sysconfdir" >> $config_host_mak
>  echo "docdir=$docdir" >> $config_host_mak
>  echo "confdir=$confdir" >> $config_host_mak
> +echo "libexecdir=\${prefix}/libexec" >> $config_host_mak
>
>  case "$cpu" in
>   
> i386|x86_64|alpha|cris|hppa|ia64|lm32|m68k|microblaze|mips|mips64|ppc|ppc64|s390|s390x|sparc|sparc64|unicore32)
> diff --git a/qemu-bridge-helper.c b/qemu-bridge-helper.c
> new file mode 100644
> index 0000000..2ce82fb
> --- /dev/null
> +++ b/qemu-bridge-helper.c
> @@ -0,0 +1,205 @@
> +/*
> + * QEMU Bridge Helper
> + *
> + * Copyright IBM, Corp. 2011
> + *
> + * Authors:
> + * Anthony Liguori   <address@hidden>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include "config-host.h"
> +
> +#include <stdio.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <string.h>
> +#include <stdlib.h>
> +#include <ctype.h>
> +
> +#include <sys/types.h>
> +#include <sys/ioctl.h>
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +#include <sys/prctl.h>
> +
> +#include <net/if.h>
> +
> +#include <linux/sockios.h>
> +
> +#include "net/tap-linux.h"
> +
> +static int has_vnet_hdr(int fd)
> +{
> +    unsigned int features = 0;
> +    struct ifreq ifreq;
> +
> +    if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
> +        return -errno;
> +    }
> +
> +    if (!(features & IFF_VNET_HDR)) {
> +        return -ENOTSUP;
> +    }
> +
> +    if (ioctl(fd, TUNGETIFF, &ifreq) != -1 || errno != EBADFD) {
> +        return -ENOTSUP;
> +    }
> +
> +    return 1;
> +}
> +
> +static void prep_ifreq(struct ifreq *ifr, const char *ifname)
> +{
> +    memset(ifr, 0, sizeof(*ifr));
> +    snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
> +}
> +
> +static int send_fd(int c, int fd)
> +{
> +    char msgbuf[CMSG_SPACE(sizeof(fd))];
> +    struct msghdr msg = {
> +        .msg_control = msgbuf,
> +        .msg_controllen = sizeof(msgbuf),
> +    };
> +    struct cmsghdr *cmsg;
> +    struct iovec iov;
> +    char req[1] = { 0x00 };
> +
> +    cmsg = CMSG_FIRSTHDR(&msg);
> +    cmsg->cmsg_level = SOL_SOCKET;
> +    cmsg->cmsg_type = SCM_RIGHTS;
> +    cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
> +    msg.msg_controllen = cmsg->cmsg_len;
> +
> +    iov.iov_base = req;
> +    iov.iov_len = sizeof(req);
> +
> +    msg.msg_iov = &iov;
> +    msg.msg_iovlen = 1;
> +    memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
> +
> +    return sendmsg(c, &msg, 0);
> +}
> +
> +int main(int argc, char **argv)
> +{
> +    struct ifreq ifr;
> +    int fd, ctlfd, unixfd;
> +    int use_vnet = 0;
> +    int mtu;
> +    const char *bridge;
> +    char iface[IFNAMSIZ];
> +    int index;
> +
> +    /* parse arguments */
> +    if (argc < 3 || argc > 4) {
> +        fprintf(stderr, "Usage: %s [--use-vnet] BRIDGE FD\n", argv[0]);
> +        return 1;
> +    }
> +
> +    index = 1;
> +    if (strcmp(argv[index], "--use-vnet") == 0) {
> +        use_vnet = 1;
> +        index++;
> +        if (argc == 3) {
> +            fprintf(stderr, "invalid number of arguments\n");
> +            return -1;
> +        }
> +    }
> +
> +    bridge = argv[index++];
> +    unixfd = atoi(argv[index++]);
> +
> +    /* open a socket to use to control the network interfaces */
> +    ctlfd = socket(AF_INET, SOCK_STREAM, 0);
> +    if (ctlfd == -1) {
> +        fprintf(stderr, "failed to open control socket\n");
> +        return -errno;
> +    }
> +
> +    /* open the tap device */
> +    fd = open("/dev/net/tun", O_RDWR);
> +    if (fd == -1) {
> +        fprintf(stderr, "failed to open /dev/net/tun\n");
> +        return -errno;
> +    }
> +
> +    /* request a tap device, disable PI, and add vnet header support if
> +     * requested and it's available. */
> +    prep_ifreq(&ifr, "tap%d");
> +    ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
> +    if (use_vnet && has_vnet_hdr(fd)) {
> +        ifr.ifr_flags |= IFF_VNET_HDR;
> +    }
> +
> +    if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
> +        fprintf(stderr, "failed to create tun device\n");
> +        return -errno;
> +    }
> +
> +    /* save tap device name */
> +    snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
> +
> +    /* get the mtu of the bridge */
> +    prep_ifreq(&ifr, bridge);
> +    if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
> +        fprintf(stderr, "failed to get mtu of bridge `%s'\n", bridge);
> +        return -errno;
> +    }
> +
> +    /* save mtu */
> +    mtu = ifr.ifr_mtu;
> +
> +    /* set the mtu of the interface based on the bridge */
> +    prep_ifreq(&ifr, iface);
> +    ifr.ifr_mtu = mtu;
> +    if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
> +        fprintf(stderr, "failed to set mtu of device `%s' to %d\n",
> +                iface, mtu);
> +        return -errno;
> +    }
> +
> +    /* add the interface to the bridge */
> +    prep_ifreq(&ifr, bridge);
> +    ifr.ifr_ifindex = if_nametoindex(iface);
> +
> +    if (ioctl(ctlfd, SIOCBRADDIF, &ifr) == -1) {
> +        fprintf(stderr, "failed to add interface `%s' to bridge `%s'\n",
> +                iface, bridge);
> +        return -errno;
> +    }
> +
> +    /* bring the interface up */
> +    prep_ifreq(&ifr, iface);
> +    if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
> +        fprintf(stderr, "failed to get interface flags for `%s'\n", iface);
> +        return -errno;
> +    }
> +
> +    ifr.ifr_flags |= IFF_UP;
> +    if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
> +        fprintf(stderr, "failed to set bring up interface `%s'\n", iface);
> +        return -errno;
> +    }

It looks like only the above series of ioctls is Linux specific. I'm
not familiar if other OS could support similar bridges, if so, it
would be better to contain the bridge setup in a separate function.
This can be done later though.

> +
> +    /* write fd to the domain socket */
> +    if (send_fd(unixfd, fd) == -1) {
> +        fprintf(stderr, "failed to write fd to unix socket\n");
> +        return -errno;
> +    }
> +
> +    /* ... */
> +
> +    /* profit! */
> +
> +    close(fd);
> +
> +    close(ctlfd);
> +
> +    return 0;
> +}
> --
> 1.7.3.4
>
>
>