Matthias Radestock
495a35a6a6
Closing a subscription can cause the associated fd to be re-used while the subscription goroutine is also still trying to use it. Which can have disastrous consequences. So as a work around we don't close subscriptions. This means we leak an fd, some buffer space, and goroutine. The latter will eventually block in a channel send of a subscription event, since nothing is left reading ont the other end. So at least it won't be consuming cycles.
85 lines
2.3 KiB
Go
85 lines
2.3 KiB
Go
package net
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import (
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"fmt"
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"net"
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"syscall"
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"github.com/vishvananda/netlink"
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)
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// Wait for an interface to come up.
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func EnsureInterface(ifaceName string) (*net.Interface, error) {
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iface, err := ensureInterface(ifaceName)
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if err != nil {
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return nil, err
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}
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return iface, err
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}
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func ensureInterface(ifaceName string) (*net.Interface, error) {
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ch := make(chan netlink.LinkUpdate)
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// NB: We do not supply (and eventually close) a 'done' channel
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// here since that can cause incorrect file descriptor
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// re-usage. See https://github.com/weaveworks/weave/issues/2120
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if err := netlink.LinkSubscribe(ch, nil); err != nil {
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return nil, err
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}
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// check for currently-existing interface after subscribing, to avoid race
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if iface, err := findInterface(ifaceName); err == nil {
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return iface, nil
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}
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for update := range ch {
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if ifaceName == update.Link.Attrs().Name && update.IfInfomsg.Flags&syscall.IFF_UP != 0 {
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break
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}
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}
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iface, err := findInterface(ifaceName)
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return iface, err
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}
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// Wait for an interface to come up and have a route added to the multicast subnet.
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// This matches the behaviour in 'weave attach', which is the only context in which
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// we expect this to be called. If you change one, change the other to match.
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func EnsureInterfaceAndMcastRoute(ifaceName string) (*net.Interface, error) {
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iface, err := ensureInterface(ifaceName)
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if err != nil {
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return nil, err
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}
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ch := make(chan netlink.RouteUpdate)
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if err := netlink.RouteSubscribe(ch, nil); err != nil {
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return nil, err
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}
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dest := net.IPv4(224, 0, 0, 0)
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check := func(route netlink.Route) bool {
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return route.Dst != nil && route.Dst.IP.Equal(dest)
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}
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// check for currently-existing route after subscribing, to avoid race
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routes, err := netlink.RouteList(nil, netlink.FAMILY_V4)
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if err != nil {
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return nil, err
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}
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for _, route := range routes {
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if check(route) {
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return iface, nil
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}
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}
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for update := range ch {
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if check(update.Route) {
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return iface, nil
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}
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}
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// should never get here
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return iface, nil
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}
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func findInterface(ifaceName string) (iface *net.Interface, err error) {
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if iface, err = net.InterfaceByName(ifaceName); err != nil {
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return iface, fmt.Errorf("Unable to find interface %s", ifaceName)
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}
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if 0 == (net.FlagUp & iface.Flags) {
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return iface, fmt.Errorf("Interface %s is not up", ifaceName)
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}
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return
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}
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