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watcher.go
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watcher.go
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//go:build linux
// Copyright Red Hat / IBM
// Copyright Grafana Labs
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// This implementation is a derivation of the code in
// https://github.com/netobserv/netobserv-ebpf-agent/tree/release-1.4
package ifaces
import (
"context"
"log/slog"
"syscall"
"github.com/vishvananda/netlink"
)
// Watcher uses system's netlink to get real-time information events about network interfaces'
// addition or removal.
type Watcher struct {
bufLen int
current map[Interface]struct{}
interfaces func() ([]Interface, error)
// linkSubscriber abstracts netlink.LinkSubscribe implementation, allowing the injection of
// mocks for unit testing
linkSubscriber func(ch chan<- netlink.LinkUpdate, done <-chan struct{}) error
}
func NewWatcher(bufLen int) *Watcher {
return &Watcher{
bufLen: bufLen,
current: map[Interface]struct{}{},
interfaces: netInterfaces,
linkSubscriber: netlink.LinkSubscribe,
}
}
func (w *Watcher) Subscribe(ctx context.Context) (<-chan Event, error) {
out := make(chan Event, w.bufLen)
go w.sendUpdates(ctx, out)
return out, nil
}
func (w *Watcher) sendUpdates(ctx context.Context, out chan Event) {
log := slog.With("component", "ifaces.Watcher")
// subscribe for interface events
links := make(chan netlink.LinkUpdate)
if err := w.linkSubscriber(links, ctx.Done()); err != nil {
log.Error("can't subscribe to links", "error", err)
return
}
// before sending netlink updates, send all the existing interfaces at the moment of starting
// the Watcher
if names, err := w.interfaces(); err != nil {
log.Error("can't fetch network interfaces. You might be missing flows", "error", err)
} else {
for _, name := range names {
w.current[name] = struct{}{}
out <- Event{Type: EventAdded, Interface: name}
}
}
for link := range links {
attrs := link.Attrs()
if attrs == nil {
log.Debug("received link update without attributes. Ignoring", "link", link)
continue
}
iface := Interface{Name: attrs.Name, Index: attrs.Index}
if link.Flags&(syscall.IFF_UP|syscall.IFF_RUNNING) != 0 {
log.Debug("Interface up and running",
"operstate", attrs.OperState,
"flags", attrs.Flags,
"name", attrs.Name)
if _, ok := w.current[iface]; !ok {
w.current[iface] = struct{}{}
out <- Event{Type: EventAdded, Interface: iface}
}
} else {
log.Debug("Interface down or not running",
"operstate", attrs.OperState,
"flags", attrs.Flags,
"name", attrs.Name)
if _, ok := w.current[iface]; ok {
delete(w.current, iface)
out <- Event{Type: EventDeleted, Interface: iface}
}
}
}
}