From 25b1d7134115373c56db235ae4eb9d57e0738d4f Mon Sep 17 00:00:00 2001
From: Lucas Manning <lucasmanning@google.com>
Date: Wed, 15 Jan 2025 17:41:24 -0800
Subject: [PATCH] Add constants and types related to the implementation of
 PACKET_MMAP.

This is the first in a series of changes that implements PACKET_MMAP.

PiperOrigin-RevId: 716014872
---
 pkg/abi/linux/socket.go | 66 +++++++++++++++++++++++++++++++++++++++++
 pkg/syserr/netstack.go  |  3 ++
 pkg/tcpip/errors.go     | 18 +++++++++++
 pkg/tcpip/tcpip.go      | 13 ++++++++
 4 files changed, 100 insertions(+)

diff --git a/pkg/abi/linux/socket.go b/pkg/abi/linux/socket.go
index 2905f73ed..2efd17c60 100644
--- a/pkg/abi/linux/socket.go
+++ b/pkg/abi/linux/socket.go
@@ -144,6 +144,72 @@ const (
 	PACKET_OUTGOING  = 4 // Outgoing of any type
 )
 
+// Packet socket options from <linux/if_packet.h>
+const (
+	PACKET_RX_RING = 5
+)
+
+// Statuses for a frame in a packet_mmap ring buffer from <linux/if_packet.h>.
+const (
+	TP_STATUS_KERNEL          = 0
+	TP_STATUS_USER            = 0x1
+	TP_STATUS_COPY            = 0x2
+	TP_STATUS_LOSING          = 0x4
+	TP_STATUS_CSUM_NOT_READY  = 0x8
+	TP_STATUS_VLAN_VALID      = 0x10
+	TP_STATUS_BLK_TMO         = 0x20
+	TP_STATUS_VLAN_TPID_VALID = 0x40
+	TP_STATUS_CSUM_VALID      = 0x80
+	TP_STATUS_GSO_TCP         = 0x100
+)
+
+// TpacketReq is the request for a packet_mmap ring buffer from
+// <linux/if_packet.h>.
+//
+// +marshal
+type TpacketReq struct {
+	TpBlockSize uint32
+	TpBlockNr   uint32
+	TpFrameSize uint32
+	TpFrameNr   uint32
+}
+
+// TpacketHdr is the header for a frame in a packet_mmap ring buffer from
+// <linux/if_packet.h>.
+//
+// +marshal
+type TpacketHdr struct {
+	TpStatus  uint64
+	TpLen     uint32
+	TpSnaplen uint32
+	TpMac     uint16
+	TpNet     uint16
+	TpSec     uint32
+	TpUsec    uint32 `marshal:"unaligned"`
+}
+
+// TpacketAlignment is the alignment of a frame in a packet_mmap ring buffer
+// from <linux/if_packet.h>.
+const (
+	TPACKET_ALIGNMENT = 16
+)
+
+// TPACKET_V1 is the version of a packet_mmap ring buffer from
+// <linux/if_packet.h> that is implemented in gVisor.
+const (
+	TPACKET_V1 = iota
+)
+
+// TPACKET_HDRLEN is the length of a TpacketHdr from <linux/if_packet.h>.
+var (
+	TPACKET_HDRLEN = TPacketAlign(uint32((*TpacketHdr)(nil).SizeBytes()) + uint32((*SockAddrLink)(nil).SizeBytes()))
+)
+
+// TPacketAlign aligns a value to the alignment of a TPacket.
+func TPacketAlign(x uint32) uint32 {
+	return (x + TPACKET_ALIGNMENT - 1) &^ (TPACKET_ALIGNMENT - 1)
+}
+
 // Socket options from socket.h.
 const (
 	SO_DEBUG                 = 1
diff --git a/pkg/syserr/netstack.go b/pkg/syserr/netstack.go
index 3928106da..0cbcdd595 100644
--- a/pkg/syserr/netstack.go
+++ b/pkg/syserr/netstack.go
@@ -55,6 +55,7 @@ var (
 	ErrMulticastInputCannotBeOutput = New((&tcpip.ErrMulticastInputCannotBeOutput{}).String(), errno.EINVAL)
 	ErrMissingRequiredFields        = New((&tcpip.ErrMissingRequiredFields{}).String(), errno.EINVAL)
 	ErrNoNet                        = New((&tcpip.ErrNoNet{}).String(), errno.ENONET)
+	ErrEndpointBusy                 = New((&tcpip.ErrEndpointBusy{}).String(), errno.EBUSY)
 )
 
 // TranslateNetstackError converts an error from the tcpip package to a sentry
@@ -149,6 +150,8 @@ func TranslateNetstackError(err tcpip.Error) *Error {
 		return ErrMulticastInputCannotBeOutput
 	case *tcpip.ErrMissingRequiredFields:
 		return ErrMissingRequiredFields
+	case *tcpip.ErrEndpointBusy:
+		return ErrEndpointBusy
 	default:
 		panic(fmt.Sprintf("unknown error %T", err))
 	}
diff --git a/pkg/tcpip/errors.go b/pkg/tcpip/errors.go
index 0df3d8857..f6ed36176 100644
--- a/pkg/tcpip/errors.go
+++ b/pkg/tcpip/errors.go
@@ -620,4 +620,22 @@ func (*ErrMulticastInputCannotBeOutput) IgnoreStats() bool {
 }
 func (*ErrMulticastInputCannotBeOutput) String() string { return "output cannot contain input" }
 
+// ErrEndpointBusy indicates that the operation cannot be completed because the
+// endpoint is busy.
+//
+// +stateify savable
+type ErrEndpointBusy struct{}
+
+// isError implements Error.
+func (*ErrEndpointBusy) isError() {}
+
+// IgnoreStats implements Error.
+func (*ErrEndpointBusy) IgnoreStats() bool {
+	return true
+}
+
+func (*ErrEndpointBusy) String() string {
+	return "operation cannot be completed because the endpoint is busy"
+}
+
 // LINT.ThenChange(../syserr/netstack.go)
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index cea7530c2..970fe21d2 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -1185,6 +1185,19 @@ func (*ICMPv6Filter) isGettableSocketOption() {}
 
 func (*ICMPv6Filter) isSettableSocketOption() {}
 
+// TpacketReq is the tpacket_req structure as described in
+// https://www.kernel.org/doc/Documentation/networking/packet_mmap.txt
+//
+// +stateify savable
+type TpacketReq struct {
+	TpBlockSize uint32
+	TpBlockNr   uint32
+	TpFrameSize uint32
+	TpFrameNr   uint32
+}
+
+func (*TpacketReq) isSettableSocketOption() {}
+
 // EndpointState represents the state of an endpoint.
 type EndpointState uint8