Hello Ivan,

>This option will make --dump-dmesg save only the part of the dmesg
>buffer since it was last cleared on the crashed kernel (with
>dmesg --clear and such) instead of the whole buffer since boot or
>wrap-around. It works on kernels with commit f468908bb55a ("printk:
>add clear_idx symbol to vmcoreinfo") merged in v4.6 and otherwise
>will default to the regular behavior.
>
>Signed-off-by: Ivan Delalande <[email protected]>

Thanks, I'll merge this patch into v1.6.2.

Regards,
Atsushi Kumagai

>---
> makedumpfile.8 |  8 +++++++-
> makedumpfile.c | 24 ++++++++++++++++++++++--
> makedumpfile.h |  3 +++
> 3 files changed, 32 insertions(+), 3 deletions(-)
>
>diff --git a/makedumpfile.8 b/makedumpfile.8
>index 9932364..76a8d6e 100644
>--- a/makedumpfile.8
>+++ b/makedumpfile.8
>@@ -20,7 +20,7 @@ makedumpfile \- make a small dumpfile of kdump
> .br
> \fBmakedumpfile\fR    [\fIOPTION\fR] [\-\-xen-syms 
> \fIXEN-SYMS\fR|\-\-xen-vmcoreinfo \fIVMCOREINFO\fR] \fIVMCORE\fR
>\fIDUMPFILE\fR
> .br
>-\fBmakedumpfile\fR \-\-dump-dmesg [\-x \fIVMLINUX\fR|\-i \fIVMCOREINFO\fR] 
>\fIVMCORE\fR \fILOGFILE\fR
>+\fBmakedumpfile\fR \-\-dump-dmesg [\-\-partial-dmesg] [\-x \fIVMLINUX\fR|\-i 
>\fIVMCOREINFO\fR] \fIVMCORE\fR
>\fILOGFILE\fR
> .br
> \fBmakedumpfile\fR    [\fIOPTION\fR] \-x \fIVMLINUX\fR 
> \-\-diskset=\fIVMCORE1\fR \-\-diskset=\fIVMCORE2\fR
>[\-\-diskset=\fIVMCORE3\fR ..] \fIDUMPFILE\fR
> .br
>@@ -586,6 +586,12 @@ it is necessary to specfiy [\-x \fIVMLINUX\fR] or [\-i 
>\fIVMCOREINFO\fR].
>
>
> .TP
>+\fB\-\-partial-dmesg\fR
>+This option will make --dump-dmesg extract only dmesg logs since that buffer 
>was
>+last cleared on the crashed kernel, through "dmesg --clear" for example.
>+
>+
>+.TP
> \fB\-\-mem-usage\fR
> This option is only for x86_64.
> This option is used to show the page numbers of current system in different
>diff --git a/makedumpfile.c b/makedumpfile.c
>index 95cc5ef..6c5fa4c 100644
>--- a/makedumpfile.c
>+++ b/makedumpfile.c
>@@ -1498,6 +1498,7 @@ get_symbol_info(void)
>       SYMBOL_INIT(log_buf_len, "log_buf_len");
>       SYMBOL_INIT(log_end, "log_end");
>       SYMBOL_INIT(log_first_idx, "log_first_idx");
>+      SYMBOL_INIT(clear_idx, "clear_idx");
>       SYMBOL_INIT(log_next_idx, "log_next_idx");
>       SYMBOL_INIT(max_pfn, "max_pfn");
>       SYMBOL_INIT(modules, "modules");
>@@ -2115,6 +2116,7 @@ write_vmcoreinfo_data(void)
>       WRITE_SYMBOL("log_buf_len", log_buf_len);
>       WRITE_SYMBOL("log_end", log_end);
>       WRITE_SYMBOL("log_first_idx", log_first_idx);
>+      WRITE_SYMBOL("clear_idx", clear_idx);
>       WRITE_SYMBOL("log_next_idx", log_next_idx);
>       WRITE_SYMBOL("max_pfn", max_pfn);
>       WRITE_SYMBOL("high_memory", high_memory);
>@@ -2509,6 +2511,7 @@ read_vmcoreinfo(void)
>       READ_SYMBOL("log_buf_len", log_buf_len);
>       READ_SYMBOL("log_end", log_end);
>       READ_SYMBOL("log_first_idx", log_first_idx);
>+      READ_SYMBOL("clear_idx", clear_idx);
>       READ_SYMBOL("log_next_idx", log_next_idx);
>       READ_SYMBOL("max_pfn", max_pfn);
>       READ_SYMBOL("high_memory", high_memory);
>@@ -5025,6 +5028,7 @@ dump_dmesg()
>       int log_buf_len, length_log, length_oldlog, ret = FALSE;
>       unsigned long index, log_buf, log_end;
>       unsigned int idx, log_first_idx, log_next_idx;
>+      unsigned long long first_idx_sym;
>       unsigned long log_end_2_6_24;
>       unsigned      log_end_2_6_25;
>       char *log_buffer = NULL, *log_ptr = NULL;
>@@ -5058,7 +5062,13 @@ dump_dmesg()
>                       ERRMSG("Can't find variable-length record symbols");
>                       return FALSE;
>               } else {
>-                      if (!readmem(VADDR, SYMBOL(log_first_idx), 
>&log_first_idx,
>+                      if (info->flag_partial_dmesg
>+                          && SYMBOL(clear_idx) != NOT_FOUND_SYMBOL)
>+                              first_idx_sym = SYMBOL(clear_idx);
>+                      else
>+                              first_idx_sym = SYMBOL(log_first_idx);
>+
>+                      if (!readmem(VADDR, first_idx_sym, &log_first_idx,
>                           sizeof(log_first_idx))) {
>                               ERRMSG("Can't get log_first_idx.\n");
>                               return FALSE;
>@@ -5102,7 +5112,10 @@ dump_dmesg()
>       DEBUG_MSG("log_buf       : %lx\n", log_buf);
>       DEBUG_MSG("log_end       : %lx\n", log_end);
>       DEBUG_MSG("log_buf_len   : %d\n", log_buf_len);
>-      DEBUG_MSG("log_first_idx : %u\n", log_first_idx);
>+      if (info->flag_partial_dmesg)
>+              DEBUG_MSG("clear_idx : %u\n", log_first_idx);
>+      else
>+              DEBUG_MSG("log_first_idx : %u\n", log_first_idx);
>       DEBUG_MSG("log_next_idx  : %u\n", log_next_idx);
>
>       if ((log_buffer = malloc(log_buf_len)) == NULL) {
>@@ -10618,6 +10631,9 @@ check_param_for_creating_dumpfile(int argc, char 
>*argv[])
>               }
>       }
>
>+      if (info->flag_partial_dmesg && !info->flag_dmesg)
>+              return FALSE;
>+
>       if ((argc == optind + 2) && !info->flag_flatten
>                                && !info->flag_split
>                                && !info->flag_sadump_diskset) {
>@@ -11022,6 +11038,7 @@ static struct option longopts[] = {
>       {"message-level", required_argument, NULL, OPT_MESSAGE_LEVEL},
>       {"vtop", required_argument, NULL, OPT_VTOP},
>       {"dump-dmesg", no_argument, NULL, OPT_DUMP_DMESG},
>+      {"partial-dmesg", no_argument, NULL, OPT_PARTIAL_DMESG},
>       {"config", required_argument, NULL, OPT_CONFIG},
>       {"help", no_argument, NULL, OPT_HELP},
>       {"diskset", required_argument, NULL, OPT_DISKSET},
>@@ -11135,6 +11152,9 @@ main(int argc, char *argv[])
>               case OPT_DUMP_DMESG:
>                       info->flag_dmesg = 1;
>                       break;
>+              case OPT_PARTIAL_DMESG:
>+                      info->flag_partial_dmesg = 1;
>+                      break;
>               case OPT_MEM_USAGE:
>                      info->flag_mem_usage = 1;
>                      break;
>diff --git a/makedumpfile.h b/makedumpfile.h
>index 6ea8cc4..d3b7532 100644
>--- a/makedumpfile.h
>+++ b/makedumpfile.h
>@@ -1241,6 +1241,7 @@ struct DumpInfo {
>       int             flag_force;          /* overwrite existing stuff */
>       int             flag_exclude_xen_dom;/* exclude Domain-U from xen-kdump 
> */
>       int             flag_dmesg;          /* dump the dmesg log out of the 
> vmcore file */
>+      int             flag_partial_dmesg;  /* dmesg dump only from the last 
>cleared index*/
>       int             flag_mem_usage;  /*show the page number of memory in 
> different use*/
>       int             flag_use_printk_log; /* did we read printk_log symbol 
> name? */
>       int             flag_nospace;        /* the flag of "No space on 
> device" error */
>@@ -1529,6 +1530,7 @@ struct symbol_table {
>       unsigned long long      log_buf_len;
>       unsigned long long      log_end;
>       unsigned long long      log_first_idx;
>+      unsigned long long      clear_idx;
>       unsigned long long      log_next_idx;
>       unsigned long long      max_pfn;
>       unsigned long long      node_remap_start_vaddr;
>@@ -2268,6 +2270,7 @@ struct elf_prstatus {
> #define OPT_SPLITBLOCK_SIZE   OPT_START+14
> #define OPT_WORKING_DIR         OPT_START+15
> #define OPT_NUM_THREADS       OPT_START+16
>+#define OPT_PARTIAL_DMESG     OPT_START+17
>
> /*
>  * Function Prototype.
>--
>2.13.1


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