On Sun, May 3, 2020 at 11:28 PM Yonghong Song <yhs@xxxxxx> wrote:
>
> Macro DEFINE_BPF_ITER_FUNC is implemented so target
> can define an init function to capture the BTF type
> which represents the target.
>
> The bpf_iter_meta is a structure holding meta data, common
> to all targets in the bpf program.
>
> Additional marker functions are called before/after
> bpf_seq_read() show() and stop() callback functions
> to help calculate precise seq_num and whether call bpf_prog
> inside stop().
>
> Two functions, bpf_iter_get_info() and bpf_iter_run_prog(),
> are implemented so target can get needed information from
> bpf_iter infrastructure and can run the program.
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
> include/linux/bpf.h | 11 +++++
> kernel/bpf/bpf_iter.c | 94 ++++++++++++++++++++++++++++++++++++++++---
> 2 files changed, 100 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 26daf85cba10..70c71c3cd9e8 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1129,6 +1129,9 @@ int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
> int bpf_obj_get_user(const char __user *pathname, int flags);
>
> #define BPF_ITER_FUNC_PREFIX "__bpf_iter__"
> +#define DEFINE_BPF_ITER_FUNC(target, args...) \
> + extern int __bpf_iter__ ## target(args); \
> + int __init __bpf_iter__ ## target(args) { return 0; }
Why is extern declaration needed here? Doesn't the same macro define
global function itself? I'm probably missing some C semantics thingy,
sorry...
>
> typedef int (*bpf_iter_init_seq_priv_t)(void *private_data);
> typedef void (*bpf_iter_fini_seq_priv_t)(void *private_data);
> @@ -1141,11 +1144,19 @@ struct bpf_iter_reg {
> u32 seq_priv_size;
> };
>
> +struct bpf_iter_meta {
> + __bpf_md_ptr(struct seq_file *, seq);
> + u64 session_id;
> + u64 seq_num;
> +};
> +
[...]
> /* bpf_seq_read, a customized and simpler version for bpf iterator.
> * no_llseek is assumed for this file.
> * The following are differences from seq_read():
> @@ -83,12 +119,15 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,
> if (!p || IS_ERR(p))
> goto Stop;
>
> + bpf_iter_inc_seq_num(seq);
so seq_num is one-based, not zero-based? So on first show() call it
will be set to 1, not 0, right?
> err = seq->op->show(seq, p);
> if (seq_has_overflowed(seq)) {
> + bpf_iter_dec_seq_num(seq);
> err = -E2BIG;
> goto Error_show;
> } else if (err) {
> /* < 0: go out, > 0: skip */
> + bpf_iter_dec_seq_num(seq);
> if (likely(err < 0))
> goto Error_show;
> seq->count = 0;
[...]
