test: add Linux OFD lock regression tests

		t.Fatalf("tx.Commit failed: %v", err)

	}

}

// TestOFDLockInterleavedReadersWrite verifies that after two interleaved read

// transactions on separate connections in the same process have both committed,

// a subsequent write transaction on either connection succeeds without leaking

// an OFD read lock (which would cause SQLITE_BUSY).

//

// Authored by Jan Mercl (@cznic) in https://gitlab.com/cznic/libsqlite3/-/merge_requests/3#note_3726270793.

func TestOFDLockInterleavedReadersWrite(t *testing.T) {

	dbPath := filepath.Join(t.TempDir(), "interleaved_ofd_test.db")

	db, err := sql.Open(driverName, dbPath)

	if err != nil {

		t.Fatal(err)

	}

	defer db.Close()

	ctx := context.Background()

	c1, err := db.Conn(ctx)

	if err != nil {

		t.Fatal(err)

	}

	defer c1.Close()

	c2, err := db.Conn(ctx)

	if err != nil {

		t.Fatal(err)

	}

	defer c2.Close()

	if _, err := c1.ExecContext(ctx, "CREATE TABLE t(x); INSERT INTO t VALUES(1);"); err != nil {

		t.Fatal(err)

	}

	// 1. Begin read transaction on c1 (acquires kernel OFD read lock via c1's fd).

	var count int

	if _, err := c1.ExecContext(ctx, "BEGIN;"); err != nil {

		t.Fatal(err)

	}

	if err := c1.QueryRowContext(ctx, "SELECT count(*) FROM t;").Scan(&count); err != nil {

		t.Fatal(err)

	}

	// 2. Begin read transaction on c2 while c1 is still reading.

	if _, err := c2.ExecContext(ctx, "BEGIN;"); err != nil {

		t.Fatal(err)

	}

	if err := c2.QueryRowContext(ctx, "SELECT count(*) FROM t;").Scan(&count); err != nil {

		t.Fatal(err)

	}

	// 3. Commit c1 first, then commit c2.

	if _, err := c1.ExecContext(ctx, "COMMIT;"); err != nil {

		t.Fatal(err)

	}

	if _, err := c2.ExecContext(ctx, "COMMIT;"); err != nil {

		t.Fatal(err)

	}

	// 4. Now attempt a write transaction on c2.

	// If c1's kernel OFD read lock leaked because c2's unlock was a no-op on c1's fd,

	// this write will fail with SQLITE_BUSY.

	if _, err := c2.ExecContext(ctx, "BEGIN IMMEDIATE; INSERT INTO t VALUES(2); COMMIT;"); err != nil {

		t.Fatalf("write after interleaved reads failed (leaked OFD read lock): %v", err)

	}

}

// The SHARED range of SQLite's locking protocol: SHARED_FIRST = PENDING_BYTE+2,

// SHARED_SIZE = 510, with the default PENDING_BYTE = 0x40000000.

const (

	sharedFirst = 0x40000000 + 2

	sharedSize  = 510

)

// probeSharedRange attempts a conflicting F_OFD_SETLK write lock on the SHARED

// range from an independent descriptor and returns the fcntl error: nil means

// the kernel granted it, i.e. no connection in this process holds a read lock.

func probeSharedRange(t *testing.T, dbPath string) error {

	t.Helper()

	fd, err := syscall.Open(dbPath, syscall.O_RDWR, 0)

	if err != nil {

		t.Fatal(err)

	}

	defer syscall.Close(fd)

	fl := syscall.Flock_t{Type: syscall.F_WRLCK, Whence: 0, Start: sharedFirst, Len: sharedSize}

	err = syscall.FcntlFlock(uintptr(fd), fOfdSetlk, &fl)

	if err == syscall.EINVAL {

		t.Skipf("F_OFD_SETLK unsupported on this kernel/filesystem (errno %v)", err)

	}

	return err

}

// TestOFDLockReadOnlyFirstLocker: a read-only connection takes the first lock

// on the inode, then a read-write connection joins at SHARED, which moves the

// designated locking descriptor from the read-only to the read-write one. The

// process must keep a kernel read lock on the SHARED range throughout, and the

// read-write connection must still be able to upgrade.

func TestOFDLockReadOnlyFirstLocker(t *testing.T) {

	dbPath := filepath.Join(t.TempDir(), "ofd_ro_first.db")

	ctx := context.Background()

	rw, err := sql.Open(driverName, dbPath)

	if err != nil {

		t.Fatal(err)

	}

	defer rw.Close()

	if _, err := rw.ExecContext(ctx, "CREATE TABLE t(x); INSERT INTO t VALUES(1);"); err != nil {

		t.Fatal(err)

	}

	ro, err := sql.Open(driverName, "file:"+dbPath+"?mode=ro")

	if err != nil {

		t.Fatal(err)

	}

	defer ro.Close()

	roConn, err := ro.Conn(ctx)

	if err != nil {

		t.Fatal(err)

	}

	defer roConn.Close()

	rwConn, err := rw.Conn(ctx)

	if err != nil {

		t.Fatal(err)

	}

	defer rwConn.Close()

	var n int

	// 1. The read-only connection is the first locker on the inode.

	if _, err := roConn.ExecContext(ctx, "BEGIN"); err != nil {

		t.Fatal(err)

	}

	defer roConn.ExecContext(ctx, "ROLLBACK")

	if err := roConn.QueryRowContext(ctx, "SELECT count(*) FROM t").Scan(&n); err != nil {

		t.Fatal(err)

	}

	if err := probeSharedRange(t, dbPath); err == nil {

		t.Fatal("no kernel read lock while the read-only connection is inside a read transaction")

	}

	// 2. The read-write connection joins at SHARED.

	if _, err := rwConn.ExecContext(ctx, "BEGIN"); err != nil {

		t.Fatal(err)

	}

	defer rwConn.ExecContext(ctx, "ROLLBACK")

	if err := rwConn.QueryRowContext(ctx, "SELECT count(*) FROM t").Scan(&n); err != nil {

		t.Fatal(err)

	}

	if err := probeSharedRange(t, dbPath); err == nil {

		t.Fatal("kernel granted a write lock on the SHARED range while two connections hold read transactions")

	}

	// 3. The read-write connection can still upgrade (RESERVED through the

	// migrated descriptor).

	if _, err := rwConn.ExecContext(ctx, "INSERT INTO t VALUES(2)"); err != nil {

		t.Fatal(err)

	}

}

// TestOFDLockFailedFirstLock: the first SHARED attempt on an inode fails after

// its PENDING lock succeeded (a foreign write lock covers the SHARED range

// only), that connection is closed, and another connection that kept the inode

// alive then reads. The read must not go through the closed descriptor.

func TestOFDLockFailedFirstLock(t *testing.T) {

	dbPath := filepath.Join(t.TempDir(), "ofd_failed_first.db")

	ctx := context.Background()

	setup, err := sql.Open(driverName, dbPath)

	if err != nil {

		t.Fatal(err)

	}

	if _, err := setup.ExecContext(ctx, "CREATE TABLE t(x); INSERT INTO t VALUES(1);"); err != nil {

		t.Fatal(err)

	}

	setup.Close()

	// B is open and idle for the whole test: it keeps the inode entry alive.

	dbB, err := sql.Open(driverName, dbPath)

	if err != nil {

		t.Fatal(err)

	}

	defer dbB.Close()

	connB, err := dbB.Conn(ctx)

	if err != nil {

		t.Fatal(err)

	}

	defer connB.Close()

	if err := connB.PingContext(ctx); err != nil {

		t.Fatal(err)

	}

	dbA, err := sql.Open(driverName, dbPath)

	if err != nil {

		t.Fatal(err)

	}

	connA, err := dbA.Conn(ctx)

	if err != nil {

		t.Fatal(err)

	}

	// A foreign OFD write lock on the SHARED range only (no PENDING byte), so

	// A's SHARED attempt fails only after its PENDING lock succeeded.

	fd, err := syscall.Open(dbPath, syscall.O_RDWR, 0)

	if err != nil {

		t.Fatal(err)

	}

	fl := syscall.Flock_t{Type: syscall.F_WRLCK, Whence: 0, Start: sharedFirst, Len: sharedSize}

	if err := syscall.FcntlFlock(uintptr(fd), fOfdSetlk, &fl); err != nil {

		if err == syscall.EINVAL {

			t.Skipf("F_OFD_SETLK unsupported on this kernel/filesystem (errno %v)", err)

		}

		t.Fatal(err)

	}

	var n int

	if err := connA.QueryRowContext(ctx, "SELECT count(*) FROM t").Scan(&n); err == nil {

		t.Fatal("expected SQLITE_BUSY: the foreign write lock must block the SHARED lock")

	}

	connA.Close()

	dbA.Close()       // closes A's descriptor

	syscall.Close(fd) // releases the foreign lock

	if err := connB.QueryRowContext(ctx, "SELECT count(*) FROM t").Scan(&n); err != nil {

		t.Fatalf("read on the surviving connection failed: %v", err)

	}

}