[PATCH] makedumpfile: support --partial-dmesg on 5.10+ kernels

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Ivan,

-----Original Message-----
> The new printk ringbuffer implementation added in kernel v5.10 with
> commit 896fbe20b4e2 ("printk: use the lockless ringbuffer") also
> exported a new vmcore symbol "clear_seq" to keep track where dmesg had
> been cleared like "clear_idx" on previous versions. Use it in
> dump_lockless_dmesg when --partial-dmesg is passed to find and start
> dumping messages only from that index.

Thanks for the patch.

Kernel commit 7d7a23a91c91 ("printk: use seqcount_latch for clear_seq")
changed the clear_seq, the patch does not work correctly on 5.13+ kernels.

But the commit exported these values to vmcoreinfo:

SIZE(latched_seq)=24
OFFSET(latched_seq.val)=8

Can it support also 5.13+ with these?

Thanks,
Kazu

> 
> Signed-off-by: Ivan Delalande <colona at arista.com>
> ---
>  makedumpfile.c |  3 +++
>  makedumpfile.h |  1 +
>  printk.c       | 10 ++++++++++
>  3 files changed, 14 insertions(+)
> 
> diff --git a/makedumpfile.c b/makedumpfile.c
> index b1b3b42..caf4d12 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -1555,6 +1555,7 @@ get_symbol_info(void)
>  	SYMBOL_INIT(pgdat_list, "pgdat_list");
>  	SYMBOL_INIT(contig_page_data, "contig_page_data");
>  	SYMBOL_INIT(prb, "prb");
> +	SYMBOL_INIT(clear_seq, "clear_seq");
>  	SYMBOL_INIT(log_buf, "log_buf");
>  	SYMBOL_INIT(log_buf_len, "log_buf_len");
>  	SYMBOL_INIT(log_end, "log_end");
> @@ -2231,6 +2232,7 @@ write_vmcoreinfo_data(void)
>  	WRITE_SYMBOL("pgdat_list", pgdat_list);
>  	WRITE_SYMBOL("contig_page_data", contig_page_data);
>  	WRITE_SYMBOL("prb", prb);
> +	WRITE_SYMBOL("clear_seq", clear_seq);
>  	WRITE_SYMBOL("log_buf", log_buf);
>  	WRITE_SYMBOL("log_buf_len", log_buf_len);
>  	WRITE_SYMBOL("log_end", log_end);
> @@ -2676,6 +2678,7 @@ read_vmcoreinfo(void)
>  	READ_SYMBOL("pgdat_list", pgdat_list);
>  	READ_SYMBOL("contig_page_data", contig_page_data);
>  	READ_SYMBOL("prb", prb);
> +	READ_SYMBOL("clear_seq", clear_seq);
>  	READ_SYMBOL("log_buf", log_buf);
>  	READ_SYMBOL("log_buf_len", log_buf_len);
>  	READ_SYMBOL("log_end", log_end);
> diff --git a/makedumpfile.h b/makedumpfile.h
> index ca50a89..c57ac7a 100644
> --- a/makedumpfile.h
> +++ b/makedumpfile.h
> @@ -1656,6 +1656,7 @@ struct symbol_table {
>  	unsigned long long	pgdat_list;
>  	unsigned long long	contig_page_data;
>  	unsigned long long	prb;
> +	unsigned long long	clear_seq;
>  	unsigned long long	log_buf;
>  	unsigned long long	log_buf_len;
>  	unsigned long long	log_end;
> diff --git a/printk.c b/printk.c
> index e8501c7..a160a5f 100644
> --- a/printk.c
> +++ b/printk.c
> @@ -145,6 +145,7 @@ dump_record(struct prb_map *m, unsigned long id)
>  int
>  dump_lockless_dmesg(void)
>  {
> +	unsigned long long clear_seq;
>  	unsigned long head_id;
>  	unsigned long tail_id;
>  	unsigned long kaddr;
> @@ -216,6 +217,15 @@ dump_lockless_dmesg(void)
>  			OFFSET(atomic_long_t.counter));
>  	head_id = ULONG(m.desc_ring + OFFSET(prb_desc_ring.head_id) +
>  			OFFSET(atomic_long_t.counter));
> +	if (info->flag_partial_dmesg && SYMBOL(clear_seq) != NOT_FOUND_SYMBOL) {
> +		if (!readmem(VADDR, SYMBOL(clear_seq), &clear_seq,
> +			     sizeof(clear_seq))) {
> +			ERRMSG("Can't get clear_seq.\n");
> +			goto out_text_data;
> +		}
> +		tail_id = head_id - head_id % m.desc_ring_count +
> +			  clear_seq % m.desc_ring_count;
> +	}
> 
>  	if (!open_dump_file()) {
>  		ERRMSG("Can't open output file.\n");
> --
> 2.32.0