Better strace logging for epoll syscalls.

Example:

epoll_ctl(0x3 anon_inode:[eventpoll], EPOLL_CTL_ADD, 0x6 anon_inode:[eventfd], 0x7efe2fd92a80 {events=EPOLLIN|EPOLLOUT data=0x10203040506070a}) = 0x0 (4.411µs)

epoll_wait(0x3 anon_inode:[eventpoll], 0x7efe2fd92b50 {{events=EPOLLOUT data=0x102030405060708}{events=EPOLLOUT data=0x102030405060708}{events=EPOLLOUT data=0x102030405060708}}, 0x3, 0xffffffff) = 0x3 (29.891µs)

PiperOrigin-RevId: 296258146

1 files changed, 89 insertions, 0 deletions

diff --git a/pkg/sentry/strace/epoll.go b/pkg/sentry/strace/epoll.go
new file mode 100644
index 000000000..a6e48b836
--- /dev/null
+++ b/pkg/sentry/strace/epoll.go
@@ -0,0 +1,89 @@
+// Copyright 2020 The gVisor Authors.
+//
+// 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.
+
+package strace
+
+import (
+	"fmt"
+	"strings"
+
+	"gvisor.dev/gvisor/pkg/abi"
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+func epollEvent(t *kernel.Task, eventAddr usermem.Addr) string {
+	var e linux.EpollEvent
+	if _, err := t.CopyIn(eventAddr, &e); err != nil {
+		return fmt.Sprintf("%#x {error reading event: %v}", eventAddr, err)
+	}
+	var sb strings.Builder
+	fmt.Fprintf(&sb, "%#x ", eventAddr)
+	writeEpollEvent(&sb, e)
+	return sb.String()
+}
+
+func epollEvents(t *kernel.Task, eventsAddr usermem.Addr, numEvents, maxBytes uint64) string {
+	var sb strings.Builder
+	fmt.Fprintf(&sb, "%#x {", eventsAddr)
+	addr := eventsAddr
+	for i := uint64(0); i < numEvents; i++ {
+		var e linux.EpollEvent
+		if _, err := t.CopyIn(addr, &e); err != nil {
+			fmt.Fprintf(&sb, "{error reading event at %#x: %v}", addr, err)
+			continue
+		}
+		writeEpollEvent(&sb, e)
+		if uint64(sb.Len()) >= maxBytes {
+			sb.WriteString("...")
+			break
+		}
+		if _, ok := addr.AddLength(uint64(linux.SizeOfEpollEvent)); !ok {
+			fmt.Fprintf(&sb, "{error reading event at %#x: EFAULT}", addr)
+			continue
+		}
+	}
+	sb.WriteString("}")
+	return sb.String()
+}
+
+func writeEpollEvent(sb *strings.Builder, e linux.EpollEvent) {
+	events := epollEventEvents.Parse(uint64(e.Events))
+	fmt.Fprintf(sb, "{events=%s data=[%#x, %#x]}", events, e.Data[0], e.Data[1])
+}
+
+var epollCtlOps = abi.ValueSet{
+	linux.EPOLL_CTL_ADD: "EPOLL_CTL_ADD",
+	linux.EPOLL_CTL_DEL: "EPOLL_CTL_DEL",
+	linux.EPOLL_CTL_MOD: "EPOLL_CTL_MOD",
+}
+
+var epollEventEvents = abi.FlagSet{
+	{Flag: linux.EPOLLIN, Name: "EPOLLIN"},
+	{Flag: linux.EPOLLPRI, Name: "EPOLLPRI"},
+	{Flag: linux.EPOLLOUT, Name: "EPOLLOUT"},
+	{Flag: linux.EPOLLERR, Name: "EPOLLERR"},
+	{Flag: linux.EPOLLHUP, Name: "EPULLHUP"},
+	{Flag: linux.EPOLLRDNORM, Name: "EPOLLRDNORM"},
+	{Flag: linux.EPOLLRDBAND, Name: "EPOLLRDBAND"},
+	{Flag: linux.EPOLLWRNORM, Name: "EPOLLWRNORM"},
+	{Flag: linux.EPOLLWRBAND, Name: "EPOLLWRBAND"},
+	{Flag: linux.EPOLLMSG, Name: "EPOLLMSG"},
+	{Flag: linux.EPOLLRDHUP, Name: "EPOLLRDHUP"},
+	{Flag: linux.EPOLLEXCLUSIVE, Name: "EPOLLEXCLUSIVE"},
+	{Flag: linux.EPOLLWAKEUP, Name: "EPOLLWAKEUP"},
+	{Flag: linux.EPOLLONESHOT, Name: "EPOLLONESHOT"},
+	{Flag: linux.EPOLLET, Name: "EPOLLET"},
+}