From 7d386bb5aff0d880ecc0d0356436f3c83e5fb528 Mon Sep 17 00:00:00 2001
From: Dayang Shen <dayshen@microsoft.com>
Date: Sat, 25 Mar 2023 00:10:34 +0800
Subject: [PATCH] Read /dev/kmsg in non-block mode

---
 pkg/checkers/oom/oom.go      | 28 +++++++++++++++++++++++++++-
 pkg/checkers/oom/oom_test.go |  5 ++++-
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/pkg/checkers/oom/oom.go b/pkg/checkers/oom/oom.go
index 4d51b84..0263ca8 100644
--- a/pkg/checkers/oom/oom.go
+++ b/pkg/checkers/oom/oom.go
@@ -2,10 +2,13 @@ package oom
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
+	"io"
 	"os"
 	"regexp"
 	"strings"
+	"syscall"
 
 	"github.com/Azure/kdebug/pkg/base"
 )
@@ -83,6 +86,24 @@ func (c *OOMChecker) checkOOM(ctx *base.CheckContext) (*base.CheckResult, error)
 	}
 	return result, nil
 }
+
+type nonBlockReader struct {
+	fd int
+}
+
+func (r *nonBlockReader) Read(buf []byte) (n int, err error) {
+	n, err = syscall.Read(r.fd, buf)
+	if err != nil {
+		if errors.Is(err, syscall.EAGAIN) {
+			return 0, io.EOF
+		}
+	}
+	if n == 0 && err == nil {
+		return 0, io.EOF
+	}
+	return n, err
+}
+
 func (c *OOMChecker) getAndParseOOMLog() ([]string, error) {
 	file, err := os.Open(c.kernLogPath)
 	if err != nil {
@@ -90,8 +111,13 @@ func (c *OOMChecker) getAndParseOOMLog() ([]string, error) {
 	}
 	defer file.Close()
 
+	fd := int(file.Fd())
+	if err = syscall.SetNonblock(fd, true); err != nil {
+		return nil, fmt.Errorf("Fail to read in non-block mode: %s", err)
+	}
+
 	var oomInfos []string
-	scanner := bufio.NewScanner(file)
+	scanner := bufio.NewScanner(&nonBlockReader{fd})
 	for scanner.Scan() {
 		tmp := scanner.Text()
 		//todo: more sophisticated OOM context
diff --git a/pkg/checkers/oom/oom_test.go b/pkg/checkers/oom/oom_test.go
index bdf7067..a138e21 100644
--- a/pkg/checkers/oom/oom_test.go
+++ b/pkg/checkers/oom/oom_test.go
@@ -33,9 +33,12 @@ func TestCheckOOMLogWhenOOM(t *testing.T) {
 		if err != nil {
 			t.Errorf("Create tmp file error:%v", err)
 		}
-		result, _ := check.Check(&base.CheckContext{
+		result, err := check.Check(&base.CheckContext{
 			Environment: environment,
 		})
+		if err != nil {
+			t.Errorf("Expect no error but got: %s", err)
+		}
 		if len(result) != 1 {
 			t.Errorf("Get unexpected OOM result length %v", len(result))
 		}