[PATCH] makedumpfile add dmesg PRINTK_CALLER id support
Edward Chron
echron at arista.com
Thu Dec 21 05:02:56 PST 2023
Submission to Project: makedumpfile
Component: dmesg
Files: printk.c makedumpfile.c makedumpfile.h
Code level patch applied against: 1.7.4++ - latest code pulled from
https://github.com/makedumpfile/makedumpfile
makedumpfile Issue #13
https://github.com/makedumpfile/makedumpfile/issues/13
Revision: #1 on 2023/12/15 per Kazu ensure spacing of dmesg output
matches dmesg -S and new dmesg caller_id
output format (space after timestamp)
Add support so that dmesg entries include the optional Linux Kernel
debug CONFIG option PRINTK_CALLER which adds an optional dmesg field
that contains the Thread Id or CPU Id that is issuing the printk to
add the message to the kernel ring buffer. If enabled, this CONFIG
option makes debugging simpler as dmesg entries for a specific
thread or CPU can be recognized.
The dmesg command supports printing the PRINTK_CALLER field. The
old syslog format (dmesg -S) and recently support was added for dmesg
using /dev/kmsg interface.
The additional field provided by PRINTK_CALLER is only present
if it was configured for the Linux kernel on the running system. The
PRINTK_CALLER is a debug option and not configured by default so the
dmesg output will only change for those kernels where the option was
configured when the kernel was built. For users who went to the
trouble to configure PRINTK_CALLER and have the extra field available
for debugging, having dmesg print the field is very helpful and so
it would be very useful to add makedumpfile support for it.
Size of the PRINTK_CALLER field is determined by the maximum number
tasks that can be run on the system which is limited by the value of
/proc/sys/kernel/pid_max as pid values are from 0 to value - 1.
This value determines the number of id digits needed by the caller id.
The PRINTK_CALLER field is printed as T<id> for a Task Id or C<id>
for a CPU Id for a printk in CPU context. The values are left space
padded and enclosed in parentheses such as:
[ T123] or [ C16]
For dmesg command the PRINTK_CALLER field when present is the last
field before the dmesg text so it makes sense to use the same format.
Signed-off-by: Ivan Delalande <colona at arista.com>
Signed-off-by: Edward Chron <echron at arista.com>
---
makedumpfile.c | 33 +++++++++++++++++++++++++++++++++
makedumpfile.h | 22 ++++++++++++++++++++++
printk.c | 27 +++++++++++++++++++++++++++
3 files changed, 82 insertions(+)
diff --git a/makedumpfile.c b/makedumpfile.c
index a6ec9d4..a427eaf 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -2118,6 +2118,7 @@ module_end:
SIZE_INIT(printk_info, "printk_info");
OFFSET_INIT(printk_info.ts_nsec, "printk_info", "ts_nsec");
OFFSET_INIT(printk_info.text_len, "printk_info", "text_len");
+ OFFSET_INIT(printk_info.caller_id, "printk_info", "caller_id");
OFFSET_INIT(atomic_long_t.counter, "atomic_long_t", "counter");
@@ -2133,6 +2134,7 @@ module_end:
OFFSET_INIT(printk_log.ts_nsec, "printk_log", "ts_nsec");
OFFSET_INIT(printk_log.len, "printk_log", "len");
OFFSET_INIT(printk_log.text_len, "printk_log", "text_len");
+ OFFSET_INIT(printk_info.caller_id, "printk_log", "caller_id");
} else {
info->flag_use_printk_ringbuffer = FALSE;
info->flag_use_printk_log = FALSE;
@@ -2462,6 +2464,7 @@ write_vmcoreinfo_data(void)
WRITE_MEMBER_OFFSET("printk_info.ts_nsec", printk_info.ts_nsec);
WRITE_MEMBER_OFFSET("printk_info.text_len", printk_info.text_len);
+ WRITE_MEMBER_OFFSET("printk_info.caller_id", printk_info.caller_id);
WRITE_MEMBER_OFFSET("atomic_long_t.counter", atomic_long_t.counter);
@@ -2470,6 +2473,7 @@ write_vmcoreinfo_data(void)
WRITE_MEMBER_OFFSET("printk_log.ts_nsec", printk_log.ts_nsec);
WRITE_MEMBER_OFFSET("printk_log.len", printk_log.len);
WRITE_MEMBER_OFFSET("printk_log.text_len", printk_log.text_len);
+ WRITE_MEMBER_OFFSET("printk_log.caller_id", printk_log.caller_id);
} else {
/* Compatibility with pre-3.11-rc4 */
WRITE_MEMBER_OFFSET("log.ts_nsec", printk_log.ts_nsec);
@@ -2921,6 +2925,7 @@ read_vmcoreinfo(void)
READ_STRUCTURE_SIZE("printk_info", printk_info);
READ_MEMBER_OFFSET("printk_info.ts_nsec", printk_info.ts_nsec);
READ_MEMBER_OFFSET("printk_info.text_len", printk_info.text_len);
+ READ_MEMBER_OFFSET("printk_info.caller_id", printk_info.caller_id);
READ_MEMBER_OFFSET("atomic_long_t.counter", atomic_long_t.counter);
@@ -2932,6 +2937,7 @@ read_vmcoreinfo(void)
READ_MEMBER_OFFSET("printk_log.ts_nsec", printk_log.ts_nsec);
READ_MEMBER_OFFSET("printk_log.len", printk_log.len);
READ_MEMBER_OFFSET("printk_log.text_len", printk_log.text_len);
+ READ_MEMBER_OFFSET("printk_log.caller_id", printk_log.caller_id);
} else {
info->flag_use_printk_ringbuffer = FALSE;
info->flag_use_printk_log = FALSE;
@@ -5604,6 +5610,33 @@ dump_log_entry(char *logptr, int fp, const char *file_name)
bufp = buf;
bufp += sprintf(buf, "[%5lld.%06ld] ", nanos, rem/1000);
+
+ if (OFFSET(printk_log.caller_id) > 0) {
+ ssize_t numspaces;
+ unsigned int pkc;
+ char idtype;
+ int digits;
+
+ /* Get id type, isolate id value in pkc for print */
+ pkc = UINT(logptr + OFFSET(printk_log.caller_id));
+ idtype = (pkc & 0x80000000) ? 'C' : 'T';
+ pkc &= ~0x80000000;
+ /* Determine size of padding space if needed */
+ digits = snprintf(NULL, 0, "%u", pkc);
+ numspaces = CALLER_ID_SIZE - digits;
+ if (numspaces > 0) {
+ char spc[16];
+
+ memset(spc, 0, sizeof(spc));
+ memset(spc, ' ', numspaces);
+ bufp += sprintf(bufp, "[%s%c%u] ", spc, idtype, pkc);
+ } else {
+ bufp += sprintf(bufp, "[%c%u] ", idtype, pkc);
+ }
+ } else {
+ bufp = stpcpy(bufp, " ");
+ }
+
indent_len = strlen(buf);
/* How much buffer space is needed in the worst case */
diff --git a/makedumpfile.h b/makedumpfile.h
index f1619c5..0a7acb5 100644
--- a/makedumpfile.h
+++ b/makedumpfile.h
@@ -2116,10 +2116,16 @@ struct offset_table {
long p_memsz;
} elf64_phdr;
+ /* The caller_id was added by the Linux-5.1 Kernel to hold
+ * the Thread id or CPU id of the caller adding a printk
+ * dmesg to the ring buffer. As such older versions of the
+ * kernel can ignore this field as it won't be filled in.
+ */
struct printk_log_s {
long ts_nsec;
long len;
long text_len;
+ long caller_id;
} printk_log;
/*
@@ -2671,6 +2677,22 @@ struct elf_prstatus {
#endif
+/*
+ * Minimum size of the id portion of the PRINTK_CALLER dmesg field if it is
+ * configured in the Linux Kernel. The size is used to pad with spaces the
+ * PRINTK_CALLER field in each dmesg. For 32 bit kernels the maximum number
+ * of PIDs supported was 2^15 so pid values 0 to 32,767 while 64 bit systems
+ * support the value specified in /proc/sys/kernel/pid_max which is capped at
+ * PID_MAX_LIMIT. We can use 7 digits as that accomodates both 32 bit and
+ * current 64 bit systems as PID_MAX_LIMIT is currently 2^22 so that will
+ * fit in 7 digits and the id will add an additional byte for the id type of
+ * either thread 'T' or CPU 'C', where the Thread ids will have much larger
+ * values, so the CPU ids will easily be accomodated. When systems exceed
+ * 7 digits that won't break anything, but print statements needing more
+ * then 7 digits will not precisely align.
+ */
+#define CALLER_ID_SIZE 7
+
/*
* Below are options which getopt_long can recognize. From OPT_START options are
* non-printable, just used for implementation.
diff --git a/printk.c b/printk.c
index 61e0b26..bfb3a96 100644
--- a/printk.c
+++ b/printk.c
@@ -114,6 +114,33 @@ dump_record(struct prb_map *m, unsigned long id)
bufp = buf;
bufp += sprintf(buf, "[%5lld.%06ld] ", nanos, rem/1000);
+
+ if (OFFSET(printk_info.caller_id) > 0) {
+ ssize_t numspaces;
+ unsigned int pkc;
+ char idtype;
+ int digits;
+
+ /* Get id type, isolate id value in pkc for print */
+ pkc = UINT(inf + OFFSET(printk_info.caller_id));
+ idtype = (pkc & 0x80000000) ? 'C' : 'T';
+ pkc &= ~0x80000000;
+ /* Determine size of padding space if needed */
+ digits = snprintf(NULL, 0, "%u", pkc);
+ numspaces = CALLER_ID_SIZE - digits;
+ if (numspaces > 0) {
+ char spc[16];
+
+ memset(spc, 0, sizeof(spc));
+ memset(spc, ' ', numspaces);
+ bufp += sprintf(bufp, "[%s%c%u] ", spc, idtype, pkc);
+ } else {
+ bufp += sprintf(bufp, "[%c%u] ", idtype, pkc);
+ }
+ } else {
+ bufp = stpcpy(bufp, " ");
+ }
+
indent_len = strlen(buf);
/* How much buffer space is needed in the worst case */
--
2.43.0
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