Fix data types for CUTime and CSTime stat fields #403 (#404)

* Fix data types for CUTime and CSTime stat fields #403

These two stat fields (CUTime and CSTime) in the /proc/[pid]/stat file should have the signed long data type according to the documentation. But currently in the code their data type is just unsigned int. This commit fixes it and adds more tests.

See for details:
* https://man7.org/linux/man-pages/man5/proc.5.html
* https://man7.org/linux/man-pages/man3/scanf.3.html

Signed-off-by: Vyacheslav Kulakov <kulakov.home@gmail.com>

fixtures.ttar

@@ -589,7 +589,7 @@ SymlinkTo: /does/not/exist
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Path: fixtures/proc/26232/stat
 Lines: 1
-33 (ata_sff) S 2 0 0 0 -1 69238880 0 0 0 0 0 0 0 0 0 -20 1 0 5 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 17 1 0 0 0 0 0 0 0 0 0 0 0 0 0
+33 (ata_sff) S 2 0 0 0 -1 69238880 0 0 0 0 0 0 -9223372036854775808 9223372036854775807 0 -20 1 0 5 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 -9223372036854775808 9223372036854775807 0 0 0 0 0 0 0 0 0 0 0 0 0
 Mode: 644
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Path: fixtures/proc/26232/wchan

proc_stat.go

@@ -81,10 +81,10 @@ type ProcStat struct {
 	STime uint
 	// Amount of time that this process's waited-for children have been
 	// scheduled in user mode, measured in clock ticks.
-	CUTime uint
+	CUTime int
 	// Amount of time that this process's waited-for children have been
 	// scheduled in kernel mode, measured in clock ticks.
-	CSTime uint
+	CSTime int
 	// For processes running a real-time scheduling policy, this is the negated
 	// scheduling priority, minus one.
 	Priority int
@@ -141,6 +141,11 @@ func (p Proc) Stat() (ProcStat, error) {
 	}
 
 	s.Comm = string(data[l+1 : r])
+
+	// Check the following resources for the details about the particular stat
+	// fields and their data types:
+	// * https://man7.org/linux/man-pages/man5/proc.5.html
+	// * https://man7.org/linux/man-pages/man3/scanf.3.html
 	_, err = fmt.Fscan(
 		bytes.NewBuffer(data[r+2:]),
 		&s.State,

proc_stat_test.go

@@ -14,6 +14,7 @@
 package procfs
 
 import (
+	"math"
 	"os"
 	"testing"
 )
@@ -76,16 +77,30 @@ func TestProcStat(t *testing.T) {
 	}
 }
 
-func TestProcStatIgnored(t *testing.T) {
+func TestProcStatLimits(t *testing.T) {
 	p, err := getProcFixtures(t).Proc(26232)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	_, err = p.Stat()
+	s, err := p.Stat()
 	if err != nil {
 		t.Errorf("want not error, have %s", err)
 	}
+
+	// max values of stat int fields
+	for _, test := range []struct {
+		name string
+		want int
+		have int
+	}{
+		{name: "waited for children user time", want: math.MinInt64, have: s.CUTime},
+		{name: "waited for children system time", want: math.MaxInt64, have: s.CSTime},
+	} {
+		if test.want != test.have {
+			t.Errorf("want %s %d, have %d", test.name, test.want, test.have)
+		}
+	}
 }
 
 func TestProcStatComm(t *testing.T) {