-----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.
>
> On v5.13, commit 7d7a23a91c91 ("printk: use seqcount_latch for
> clear_seq") converted it from a simple value, and so an additional step
> is required to find and retrieve the sequence at the right offset in the
> latched_seq structure it now uses.
>
> Signed-off-by: Ivan Delalande <colona@xxxxxxxxxx>
The v2 patch tested OK on 5.12 and 5.14. Applied.
https://github.com/makedumpfile/makedumpfile/commit/bccc39c147fea2b29f98f9973614c7a6697a065d
Thanks,
Kazu
> ---
> makedumpfile.c | 12 ++++++++++++
> makedumpfile.h | 6 ++++++
> printk.c | 19 +++++++++++++++++++
> 3 files changed, 37 insertions(+)
>
> diff --git a/makedumpfile.c b/makedumpfile.c
> index b1b3b42..ac17f19 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");
> @@ -2000,6 +2001,9 @@ get_structure_info(void)
> OFFSET_INIT(printk_info.text_len, "printk_info", "text_len");
>
> OFFSET_INIT(atomic_long_t.counter, "atomic_long_t", "counter");
> +
> + SIZE_INIT(latched_seq, "latched_seq");
> + OFFSET_INIT(latched_seq.val, "latched_seq", "val");
> } else if (SIZE(printk_log) != NOT_FOUND_STRUCTURE) {
> /*
> * In kernel 3.11-rc4 the log structure name was renamed
> @@ -2231,6 +2235,7 @@ 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);
> @@ -2266,6 +2271,7 @@ write_vmcoreinfo_data(void)
> WRITE_STRUCTURE_SIZE("printk_ringbuffer", printk_ringbuffer);
> WRITE_STRUCTURE_SIZE("prb_desc", prb_desc);
> WRITE_STRUCTURE_SIZE("printk_info", printk_info);
> + WRITE_STRUCTURE_SIZE("latched_seq", latched_seq);
> } else if (info->flag_use_printk_log)
> WRITE_STRUCTURE_SIZE("printk_log", printk_log);
> else
> @@ -2335,6 +2341,8 @@ write_vmcoreinfo_data(void)
> WRITE_MEMBER_OFFSET("printk_info.text_len", printk_info.text_len);
>
> WRITE_MEMBER_OFFSET("atomic_long_t.counter", atomic_long_t.counter);
> +
> + WRITE_MEMBER_OFFSET("latched_seq.val", latched_seq.val);
> } else if (info->flag_use_printk_log) {
> WRITE_MEMBER_OFFSET("printk_log.ts_nsec", printk_log.ts_nsec);
> WRITE_MEMBER_OFFSET("printk_log.len", printk_log.len);
> @@ -2676,6 +2684,7 @@ 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);
> @@ -2784,6 +2793,9 @@ read_vmcoreinfo(void)
> READ_MEMBER_OFFSET("printk_info.text_len", printk_info.text_len);
>
> READ_MEMBER_OFFSET("atomic_long_t.counter", atomic_long_t.counter);
> +
> + READ_STRUCTURE_SIZE("latched_seq", latched_seq);
> + READ_MEMBER_OFFSET("latched_seq.val", latched_seq.val);
> } else if (SIZE(printk_log) != NOT_FOUND_STRUCTURE) {
> info->flag_use_printk_ringbuffer = FALSE;
> info->flag_use_printk_log = TRUE;
> diff --git a/makedumpfile.h b/makedumpfile.h
> index ca50a89..bd9e2f6 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;
> @@ -1749,6 +1750,7 @@ struct size_table {
> long printk_ringbuffer;
> long prb_desc;
> long printk_info;
> + long latched_seq;
>
> /*
> * for Xen extraction
> @@ -1973,6 +1975,10 @@ struct offset_table {
> long counter;
> } atomic_long_t;
>
> + struct latched_seq_s {
> + long val;
> + } latched_seq;
> +
> /*
> * symbols on ppc64 arch
> */
> diff --git a/printk.c b/printk.c
> index e8501c7..61e0b26 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 +217,24 @@ 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;
> + }
> + if (SIZE(latched_seq) != NOT_FOUND_STRUCTURE) {
> + kaddr = SYMBOL(clear_seq) + OFFSET(latched_seq.val) +
> + (clear_seq & 0x1) * sizeof(clear_seq);
> + if (!readmem(VADDR, kaddr, &clear_seq,
> + sizeof(clear_seq))) {
> + ERRMSG("Can't get latched 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");
> --
> 2.33.0
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