Add negative integration tests for stat syscalls (task 348)

Add three negative test scenarios for stat-family syscalls:
- stat-enoent: SYS_STAT on nonexistent file (ENOENT)
- stat-access-enoent: SYS_ACCESS on nonexistent file (ENOENT, since
  tests run as root and EACCES is bypassed)
- stat-fstat-ebadf: SYS_FSTAT on invalid fd 99999 (EBADF)

Each scenario verifies that ior captures the tracepoint on syscall
entry even when the syscall fails.

Amp-Thread-ID: https://ampcode.com/threads/T-019c81af-d01d-75db-8a92-37951fb1503c
Co-authored-by: Amp <amp@ampcode.com>

2 files changed, 98 insertions, 0 deletions

diff --git a/integrationtests/cmd/ioworkload/scenarios.go b/integrationtests/cmd/ioworkload/scenarios.go
index 5eb8acb..3f5ee4c 100644
--- a/integrationtests/cmd/ioworkload/scenarios.go
+++ b/integrationtests/cmd/ioworkload/scenarios.go
@@ -76,6 +76,9 @@ var scenarios = map[string]func() error{
 	"stat-statx":      statStatx,
 	"stat-access":     statAccess,
 	"stat-faccessat":  statFaccessat,
+	"stat-enoent":          statEnoent,
+	"stat-access-enoent":   statAccessEnoent,
+	"stat-fstat-ebadf":     statFstatEbadf,
 	"sync-basic":            syncBasic,
 	"sync-fdatasync":        syncFdatasync,
 	"sync-sync":             syncSync,
@@ -2009,6 +2012,69 @@ func statFaccessat() error {
 	return nil
 }
 
+// statEnoent attempts to stat a nonexistent file via raw SYS_STAT.
+// The syscall fails with ENOENT, but ior captures the enter_newstat
+// tracepoint because the filename is read on entry.
+func statEnoent() error {
+	dir, cleanup, err := makeTempDir("stat-enoent")
+	if err != nil {
+		return err
+	}
+	defer cleanup()
+
+	path := filepath.Join(dir, "stat-enoent-missing.txt")
+	pathBytes, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return fmt.Errorf("path bytes: %w", err)
+	}
+	var stat syscall.Stat_t
+	_, _, errno := syscall.Syscall(syscall.SYS_STAT, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(&stat)), 0)
+	runtime.KeepAlive(pathBytes)
+	runtime.KeepAlive(&stat)
+	if errno == 0 {
+		return fmt.Errorf("expected ENOENT, but stat succeeded")
+	}
+	return nil
+}
+
+// statAccessEnoent attempts to check access on a nonexistent file via raw
+// SYS_ACCESS. The syscall fails with ENOENT, but ior captures the
+// enter_access tracepoint because the path is read on entry.
+// We use ENOENT instead of EACCES because integration tests run as root,
+// which bypasses DAC permission checks.
+func statAccessEnoent() error {
+	dir, cleanup, err := makeTempDir("stat-access-enoent")
+	if err != nil {
+		return err
+	}
+	defer cleanup()
+
+	path := filepath.Join(dir, "access-enoent-missing.txt")
+	pathBytes, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return fmt.Errorf("path bytes: %w", err)
+	}
+	_, _, errno := syscall.Syscall(syscall.SYS_ACCESS, uintptr(unsafe.Pointer(pathBytes)), rOK, 0)
+	runtime.KeepAlive(pathBytes)
+	if errno == 0 {
+		return fmt.Errorf("expected ENOENT, but access succeeded")
+	}
+	return nil
+}
+
+// statFstatEbadf calls raw SYS_FSTAT on an invalid fd (99999).
+// The syscall fails with EBADF, but ior captures the enter_newfstat
+// tracepoint because it is recorded on syscall entry.
+func statFstatEbadf() error {
+	var stat syscall.Stat_t
+	_, _, errno := syscall.Syscall(syscall.SYS_FSTAT, 99999, uintptr(unsafe.Pointer(&stat)), 0)
+	runtime.KeepAlive(&stat)
+	if errno == 0 {
+		return fmt.Errorf("expected EBADF, but fstat succeeded")
+	}
+	return nil
+}
+
 // syncBasic opens a file, writes data, and fsyncs it.
 func syncBasic() error {
 	dir, cleanup, err := makeTempDir("sync-basic")
diff --git a/integrationtests/stat_test.go b/integrationtests/stat_test.go
index e38171a..400e61a 100644
--- a/integrationtests/stat_test.go
+++ b/integrationtests/stat_test.go
@@ -78,3 +78,35 @@ func TestStatFaccessat(t *testing.T) {
 		},
 	})
 }
+
+func TestStatEnoent(t *testing.T) {
+	runScenario(t, "stat-enoent", []ExpectedEvent{
+		{
+			PathContains: "stat-enoent-missing.txt",
+			Tracepoint:   "enter_newstat",
+			Comm:         "ioworkload",
+			MinCount:     1,
+		},
+	})
+}
+
+func TestStatAccessEnoent(t *testing.T) {
+	runScenario(t, "stat-access-enoent", []ExpectedEvent{
+		{
+			PathContains: "access-enoent-missing.txt",
+			Tracepoint:   "enter_access",
+			Comm:         "ioworkload",
+			MinCount:     1,
+		},
+	})
+}
+
+func TestStatFstatEbadf(t *testing.T) {
+	runScenario(t, "stat-fstat-ebadf", []ExpectedEvent{
+		{
+			Tracepoint: "enter_newfstat",
+			Comm:       "ioworkload",
+			MinCount:   1,
+		},
+	})
+}