test ./tools/testing/selftests/bpf/test_offload.py failed

[Jie2x Zhou <jie2x.zhou@xxxxxxxxx>]

hi,

I try to know why output following error?
I found that "disable_ifindex" file do not set read function, so return -EINVAL when do read.
Is it a bug in test_offload.py?

test output:
 selftests: bpf: test_offload.py
 Test destruction of generic XDP...
......
     raise Exception("Command failed: %s\n%s" % (proc.args, stderr))
 Exception: Command failed: cat /sys/kernel/debug/netdevsim/netdevsim0//ports/0/dev/hwstats/l3/disable_ifindex
 
 cat: /sys/kernel/debug/netdevsim/netdevsim0//ports/0/dev/hwstats/l3/disable_ifindex: Invalid argument
 not ok 20 selftests: bpf: test_offload.py # exit=1

source code:
In drivers/net/netdevsim/hwstats.c:
define NSIM_DEV_HWSTATS_FOPS(ACTION, TYPE)                     \
        {                                                       \
                .fops = {                                       \
                        .open = simple_open,                    \
                        .write = nsim_dev_hwstats_do_write,     \
                        .llseek = generic_file_llseek,          \
                        .owner = THIS_MODULE,                   \
                },                                              \
                .action = ACTION,                               \
                .type = TYPE,                                   \
        }

static const struct nsim_dev_hwstats_fops nsim_dev_hwstats_l3_disable_fops =
        NSIM_DEV_HWSTATS_FOPS(NSIM_DEV_HWSTATS_DO_DISABLE,
                              NETDEV_OFFLOAD_XSTATS_TYPE_L3);

        debugfs_create_file("disable_ifindex", 0600, hwstats->l3_ddir, hwstats,
                            &nsim_dev_hwstats_l3_disable_fops.fops);

In fs/read_write.c:
ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
{
......
        if (file->f_op->read)
                ret = file->f_op->read(file, buf, count, pos);
        else if (file->f_op->read_iter)
                ret = new_sync_read(file, buf, count, pos);
        else
                ret = -EINVAL;
......
}

best regards,