eBPF program to attach to 'SEC("kprobe/ext4_file_read_iter")' fails to load

[havefuncoding1]

Hi, I am working on a libbpf based ebpf program to monitor ext4 file i/o activities. Here is the code:

SEC("kprobe/ext4_file_read_iter")
int ext4_file_read_iter(struct pt_regs* ctx, struct kiocb *iocb, struct iov_iter *to)
{
    struct file* file = iocb->ki_filp;
    struct qstr qs = BPF_CORE_READ(file, f_path.dentry, d_name);
    ...
    return 0;
}

However, this program fails to load with following errors:

2024/05/14 00:28:11 libbpf [warn]: libbpf: prog 'ext4_file_read_iter': BPF program load failed: Permission denied
2024/05/14 00:28:11 libbpf [warn]: libbpf: prog 'ext4_file_read_iter': -- BEGIN PROG LOAD LOG --
0: R1=ctx() R10=fp0
; struct file* file = iocb->ki_filp;
0: (79) r3 = *(u64 *)(r2 +0)
R2 !read_ok 
processed 1 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
-- END PROG LOAD LOG --
2024/05/14 00:28:11 libbpf [warn]: libbpf: prog 'ext4_file_read_iter': failed to load: -13

Can someone tell me where the problem might be? My Ubuntu runs Linux kernel 6.8.0. I compared 'struct kiocb' in Linux source and vmlinux.h in my build environment, there is no difference. Really run out of ideas how to troubleshoot this further. Thanks a lot in advance for your help.

[havefuncoding1]

Figured out the problem... I should be calling "BPF_CORE_READ(iocb, ki_filp)", instead of "iocb->ki_filp".