support /proc/net/snmp

This proc file contains statistics according to [1].

[1] https://tools.ietf.org/html/rfc2013

Signed-off-by: Jianfeng Tan <henry.tjf@antfin.com>
Change-Id: I9662132085edd8a7783d356ce4237d7ac0800d94

2 files changed, 136 insertions, 1 deletions

diff --git a/pkg/sentry/fs/proc/net.go b/pkg/sentry/fs/proc/net.go
index f70239449..ec1bc1d17 100644
--- a/pkg/sentry/fs/proc/net.go
+++ b/pkg/sentry/fs/proc/net.go
@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"reflect"
 	"time"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
@@ -33,6 +34,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix"
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
+	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // newNet creates a new proc net entry.
@@ -40,7 +42,8 @@ func (p *proc) newNetDir(ctx context.Context, k *kernel.Kernel, msrc *fs.MountSo
 	var contents map[string]*fs.Inode
 	if s := p.k.NetworkStack(); s != nil {
 		contents = map[string]*fs.Inode{
-			"dev": seqfile.NewSeqFileInode(ctx, &netDev{s: s}, msrc),
+			"dev":  seqfile.NewSeqFileInode(ctx, &netDev{s: s}, msrc),
+			"snmp": seqfile.NewSeqFileInode(ctx, &netSnmp{s: s}, msrc),
 
 			// The following files are simple stubs until they are
 			// implemented in netstack, if the file contains a
@@ -195,6 +198,118 @@ func (n *netDev) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]se
 	return data, 0
 }
 
+// netSnmp implements seqfile.SeqSource for /proc/net/snmp.
+//
+// +stateify savable
+type netSnmp struct {
+	s inet.Stack
+}
+
+// NeedsUpdate implements seqfile.SeqSource.NeedsUpdate.
+func (n *netSnmp) NeedsUpdate(generation int64) bool {
+	return true
+}
+
+type snmpLine struct {
+	prefix string
+	header string
+}
+
+var snmp = []snmpLine{
+	{
+		prefix: "Ip",
+		header: "Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests OutDiscards OutNoRoutes ReasmTimeout ReasmReqds ReasmOKs ReasmFails FragOKs FragFails FragCreates",
+	},
+	{
+		prefix: "Icmp",
+		header: "InMsgs InErrors InCsumErrors InDestUnreachs InTimeExcds InParmProbs InSrcQuenchs InRedirects InEchos InEchoReps InTimestamps InTimestampReps InAddrMasks InAddrMaskReps OutMsgs OutErrors OutDestUnreachs OutTimeExcds OutParmProbs OutSrcQuenchs OutRedirects OutEchos OutEchoReps OutTimestamps OutTimestampReps OutAddrMasks OutAddrMaskReps",
+	},
+	{
+		prefix: "IcmpMsg",
+	},
+	{
+		prefix: "Tcp",
+		header: "RtoAlgorithm RtoMin RtoMax MaxConn ActiveOpens PassiveOpens AttemptFails EstabResets CurrEstab InSegs OutSegs RetransSegs InErrs OutRsts InCsumErrors",
+	},
+	{
+		prefix: "Udp",
+		header: "InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti",
+	},
+	{
+		prefix: "UdpLite",
+		header: "InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti",
+	},
+}
+
+func toSlice(a interface{}) []uint64 {
+	v := reflect.Indirect(reflect.ValueOf(a))
+	return v.Slice(0, v.Len()).Interface().([]uint64)
+}
+
+func sprintSlice(s []uint64) string {
+	if len(s) == 0 {
+		return ""
+	}
+	r := fmt.Sprint(s)
+	return r[1 : len(r)-1] // Remove "[]" introduced by fmt of slice.
+}
+
+// ReadSeqFileData implements seqfile.SeqSource.ReadSeqFileData. See Linux's
+// net/core/net-procfs.c:dev_seq_show.
+func (n *netSnmp) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]seqfile.SeqData, int64) {
+	if h != nil {
+		return nil, 0
+	}
+
+	contents := make([]string, 0, len(snmp)*2)
+	types := []interface{}{
+		&inet.StatSNMPIP{},
+		&inet.StatSNMPICMP{},
+		nil, // TODO(gvisor.dev/issue/628): Support IcmpMsg stats.
+		&inet.StatSNMPTCP{},
+		&inet.StatSNMPUDP{},
+		&inet.StatSNMPUDPLite{},
+	}
+	for i, stat := range types {
+		line := snmp[i]
+		if stat == nil {
+			contents = append(
+				contents,
+				fmt.Sprintf("%s:\n", line.prefix),
+				fmt.Sprintf("%s:\n", line.prefix),
+			)
+			continue
+		}
+		if err := n.s.Statistics(stat, line.prefix); err != nil {
+			if err == syserror.EOPNOTSUPP {
+				log.Infof("Failed to retrieve %s of /proc/net/snmp: %v", line.prefix, err)
+			} else {
+				log.Warningf("Failed to retrieve %s of /proc/net/snmp: %v", line.prefix, err)
+			}
+		}
+		var values string
+		if line.prefix == "Tcp" {
+			tcp := stat.(*inet.StatSNMPTCP)
+			// "Tcp" needs special processing because MaxConn is signed. RFC 2012.
+			values = fmt.Sprintf("%s %d %s", sprintSlice(tcp[:3]), int64(tcp[3]), sprintSlice(tcp[4:]))
+		} else {
+			values = sprintSlice(toSlice(stat))
+		}
+		contents = append(
+			contents,
+			fmt.Sprintf("%s: %s\n", line.prefix, line.header),
+			fmt.Sprintf("%s: %s\n", line.prefix, values),
+		)
+	}
+
+	data := make([]seqfile.SeqData, 0, len(snmp)*2)
+	for _, l := range contents {
+		data = append(data, seqfile.SeqData{Buf: []byte(l), Handle: (*netSnmp)(nil)})
+	}
+
+	return data, 0
+}
+
 // netUnix implements seqfile.SeqSource for /proc/net/unix.
 //
 // +stateify savable
diff --git a/pkg/sentry/inet/inet.go b/pkg/sentry/inet/inet.go
index 80f227dbe..bc6cb1095 100644
--- a/pkg/sentry/inet/inet.go
+++ b/pkg/sentry/inet/inet.go
@@ -153,3 +153,23 @@ type Route struct {
 	// GatewayAddr is the route gateway address (RTA_GATEWAY).
 	GatewayAddr []byte
 }
+
+// Below SNMP metrics are from Linux/usr/include/linux/snmp.h.
+
+// StatSNMPIP describes Ip line of /proc/net/snmp.
+type StatSNMPIP [19]uint64
+
+// StatSNMPICMP describes Icmp line of /proc/net/snmp.
+type StatSNMPICMP [27]uint64
+
+// StatSNMPICMPMSG describes IcmpMsg line of /proc/net/snmp.
+type StatSNMPICMPMSG [512]uint64
+
+// StatSNMPTCP describes Tcp line of /proc/net/snmp.
+type StatSNMPTCP [15]uint64
+
+// StatSNMPUDP describes Udp line of /proc/net/snmp.
+type StatSNMPUDP [8]uint64
+
+// StatSNMPUDPLite describes UdpLite line of /proc/net/snmp.
+type StatSNMPUDPLite [8]uint64