dmesg: add --json output format

Fixes: https://github.com/util-linux/util-linux/issues/1495
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/sys-utils/dmesg.1.adoc b/sys-utils/dmesg.1.adoc
index b45d57a46d2f96658136e97934a0d4320b68aa3a..aa689ee0ac8be38d4957e663d49b7a1ec5d2822d 100644 (file)
--- a/sys-utils/dmesg.1.adoc
+++ b/sys-utils/dmesg.1.adoc
@@ -69,6 +69,9 @@ will print messages from system daemons only. For all supported facilities see t
 *-H*, *--human*::
 Enable human-readable output. See also *--color*, *--reltime* and *--nopager*.
 
+*-J*, *--json*::
+Use JSON output format. The time output format is in "sec.usec" format only, log priority level is not decoded by default (use *--decode* to split into facility and priority), the other options to control the output format or time format are silently ignored.
+
 *-k*, *--kernel*::
 Print kernel messages.
 

diff --git a/sys-utils/dmesg.c b/sys-utils/dmesg.c
index 690a64ec55b9afb3d57e21979b5bdaf7dd3fff02..4606880ea6bfb18d57249755d6093fb00637183b 100644 (file)
--- a/sys-utils/dmesg.c
+++ b/sys-utils/dmesg.c
@@ -35,6 +35,7 @@
 #include "monotonic.h"
 #include "mangle.h"
 #include "pager.h"
+#include "jsonwrt.h"
 
 /* Close the log.  Currently a NOP. */
 #define SYSLOG_ACTION_CLOSE          0
@@ -193,6 +194,8 @@ struct dmesg_control {
        size_t          pagesize;
        unsigned int    time_fmt;       /* time format */
 
+       struct ul_jsonwrt jfmt;         /* -J formatting */
+
        unsigned int    follow:1,       /* wait for new messages */
                        end:1,          /* seek to the of buffer */
                        raw:1,          /* raw mode */
@@ -202,6 +205,7 @@ struct dmesg_control {
                        decode:1,       /* use "facility: level: " prefix */
                        pager:1,        /* pipe output into a pager */
                        color:1,        /* colorize messages */
+                       json:1,         /* JSON output */
                        force_prefix:1; /* force timestamp and decode prefix
                                           on each line */
        int             indent;         /* due to timestamps if newline */
@@ -282,6 +286,7 @@ static void __attribute__((__noreturn__)) usage(void)
        fputs(_(" -F, --file <file>           use the file instead of the kernel log buffer\n"), out);
        fputs(_(" -f, --facility <list>       restrict output to defined facilities\n"), out);
        fputs(_(" -H, --human                 human readable output\n"), out);
+       fputs(_(" -J, --json                  use JSON output format\n"), out);
        fputs(_(" -k, --kernel                display kernel messages\n"), out);
        fprintf(out,
              _(" -L, --color[=<when>]        colorize messages (%s, %s or %s)\n"), "auto", "always", "never");
@@ -742,7 +747,7 @@ static int get_next_syslog_record(struct dmesg_control *ctl,
                        continue;       /* error or empty line? */
 
                if (*begin == '<') {
-                       if (ctl->fltr_lev || ctl->fltr_fac || ctl->decode || ctl->color)
+                       if (ctl->fltr_lev || ctl->fltr_fac || ctl->decode || ctl->color || ctl->json)
                                begin = parse_faclev(begin + 1, &rec->facility,
                                                     &rec->level);
                        else
@@ -913,6 +918,12 @@ static const char *get_subsys_delimiter(const char *mesg, size_t mesg_size)
        return NULL;
 }
 
+#define is_facpri_valid(_r)    \
+           (((_r)->level > -1) && ((_r)->level < (int) ARRAY_SIZE(level_names)) && \
+            ((_r)->facility > -1) && \
+            ((_r)->facility < (int) ARRAY_SIZE(facility_names)))
+
+
 static void print_record(struct dmesg_control *ctl,
                         struct dmesg_record *rec)
 {
@@ -928,10 +939,20 @@ static void print_record(struct dmesg_control *ctl,
                return;
 
        if (!rec->mesg_size) {
-               putchar('\n');
+               if (!ctl->json)
+                       putchar('\n');
                return;
        }
 
+       if (ctl->json) {
+               if (!ul_jsonwrt_is_ready(&ctl->jfmt)) {
+                       ul_jsonwrt_init(&ctl->jfmt, stdout, 0);
+                       ul_jsonwrt_root_open(&ctl->jfmt);
+                       ul_jsonwrt_array_open(&ctl->jfmt, "dmesg");
+               }
+               ul_jsonwrt_object_open(&ctl->jfmt, NULL);
+       }
+
        /*
         * Compose syslog(2) compatible raw output -- used for /dev/kmsg for
         * backward compatibility with syslog(2) buffers only
@@ -946,10 +967,7 @@ static void print_record(struct dmesg_control *ctl,
        }
 
        /* Store decode information (facility & priority level) in a buffer */
-       if (ctl->decode &&
-           (rec->level > -1) && (rec->level < (int) ARRAY_SIZE(level_names)) &&
-           (rec->facility > -1) &&
-           (rec->facility < (int) ARRAY_SIZE(facility_names)))
+       if (!ctl->json && ctl->decode && is_facpri_valid(rec))
                snprintf(fpbuf, sizeof(fpbuf), "%-6s:%-6s: ",
                         facility_names[rec->facility].name,
                         level_names[rec->level].name);
@@ -995,7 +1013,8 @@ static void print_record(struct dmesg_control *ctl,
                ctl->lasttm = cur;
                break;
        case DMESG_TIMEFTM_TIME:
-               ctl->indent = snprintf(tsbuf, sizeof(tsbuf), "[%5ld.%06ld] ",
+               ctl->indent = snprintf(tsbuf, sizeof(tsbuf),
+                                     ctl->json ? "%5ld.%06ld" : "[%5ld.%06ld] ",
                                      (long)rec->tv.tv_sec,
                                      (long)rec->tv.tv_usec);
                break;
@@ -1018,8 +1037,15 @@ static void print_record(struct dmesg_control *ctl,
 
 full_output:
        /* Output the decode information */
-       if (*fpbuf)
+       if (*fpbuf) {
                fputs(fpbuf, stdout);
+       } else if (ctl->json && is_facpri_valid(rec)) {
+               if (ctl->decode) {
+                       ul_jsonwrt_value_s(&ctl->jfmt, "fac", facility_names[rec->facility].name);
+                       ul_jsonwrt_value_s(&ctl->jfmt, "pri", level_names[rec->level].name);
+               } else
+                       ul_jsonwrt_value_u64(&ctl->jfmt, "pri", LOG_MAKEPRI(rec->facility, rec->level));
+       }
 
        /* Output the timestamp buffer */
        if (*tsbuf) {
@@ -1028,17 +1054,17 @@ full_output:
                        dmesg_enable_color(timebreak ? DMESG_COLOR_TIMEBREAK :
                                                       DMESG_COLOR_TIME);
                if (ctl->time_fmt != DMESG_TIMEFTM_RELTIME) {
-                       fputs(tsbuf, stdout);
+                       if (ctl->json)
+                               ul_jsonwrt_value_raw(&ctl->jfmt, "time", tsbuf);
+                       else
+                               fputs(tsbuf, stdout);
                } else {
                        /*
                         * For relative timestamping, the first line's
                         * timestamp is the offset and all other lines will
                         * report an offset of 0.000000.
                         */
-                       if (!line)
-                               fputs(tsbuf, stdout);
-                       else
-                               printf("[  +0.000000] ");
+                       fputs(!line ? tsbuf : "[  +0.000000] ", stdout);
                }
                if (ctl->color)
                        color_disable();
@@ -1081,8 +1107,12 @@ full_output:
                safe_fwrite(ctl, line, mesg_size, ctl->indent, stdout);
                if (has_color)
                        color_disable();
-       } else
-               safe_fwrite(ctl, line, mesg_size, ctl->indent, stdout);
+       } else {
+               if (ctl->json)
+                       ul_jsonwrt_value_s(&ctl->jfmt, "msg", line);
+               else
+                       safe_fwrite(ctl, line, mesg_size, ctl->indent, stdout);
+       }
 
        /* Get the next line */
        if (ctl->force_prefix) {
@@ -1096,7 +1126,10 @@ full_output:
 
 done:
        free(mesg_copy);
-       putchar('\n');
+       if (ctl->json)
+               ul_jsonwrt_object_close(&ctl->jfmt);
+       else
+               putchar('\n');
 }
 
 /*
@@ -1199,7 +1232,7 @@ static int parse_kmsg_record(struct dmesg_control *ctl,
 
        /* A) priority and facility */
        if (ctl->fltr_lev || ctl->fltr_fac || ctl->decode ||
-           ctl->raw || ctl->color)
+           ctl->raw || ctl->color || ctl->json)
                p = parse_faclev(p, &rec->facility, &rec->level);
        else
                p = skip_item(p, end, ",");
@@ -1371,6 +1404,7 @@ int main(int argc, char *argv[])
                { "follow-new",    no_argument,       NULL, 'W' },
                { "human",         no_argument,       NULL, 'H' },
                { "help",          no_argument,       NULL, 'h' },
+               { "json",          no_argument,       NULL, 'J' },
                { "kernel",        no_argument,       NULL, 'k' },
                { "level",         required_argument, NULL, 'l' },
                { "since",         required_argument, NULL, OPT_SINCE },
@@ -1410,7 +1444,7 @@ int main(int argc, char *argv[])
        textdomain(PACKAGE);
        close_stdout_atexit();
 
-       while ((c = getopt_long(argc, argv, "CcDdEeF:f:HhkL::l:n:iPprSs:TtuVWwx",
+       while ((c = getopt_long(argc, argv, "CcDdEeF:f:HhJkL::l:n:iPprSs:TtuVWwx",
                                longopts, NULL)) != -1) {
 
                err_exclusive_options(c, longopts, excl, excl_st);
@@ -1449,6 +1483,9 @@ int main(int argc, char *argv[])
                        colormode = UL_COLORMODE_AUTO;
                        ctl.pager = 1;
                        break;
+               case 'J':
+                       ctl.json = 1;
+                       break;
                case 'k':
                        ctl.fltr_fac = 1;
                        setbit(ctl.facilities, FAC_BASE(LOG_KERN));
@@ -1544,6 +1581,15 @@ int main(int argc, char *argv[])
                errtryhelp(EXIT_FAILURE);
        }
 
+       if (ctl.json) {
+               ctl.time_fmt = DMESG_TIMEFTM_TIME;
+               delta = 0;
+               ctl.force_prefix = 0;
+               ctl.raw = 0;
+               ctl.noesc = 1;
+               nopager = 1;
+       }
+
        if ((is_timefmt(&ctl, RELTIME) ||
             is_timefmt(&ctl, CTIME)   ||
             is_timefmt(&ctl, ISO8601))) {
@@ -1569,7 +1615,8 @@ int main(int argc, char *argv[])
                }
 
 
-       ctl.color = colors_init(colormode, "dmesg") ? 1 : 0;
+       if (!ctl.json)
+               ctl.color = colors_init(colormode, "dmesg") ? 1 : 0;
        if (ctl.follow)
                nopager = 1;
        ctl.pager = nopager ? 0 : ctl.pager;
@@ -1591,7 +1638,6 @@ int main(int argc, char *argv[])
                /* only kmsg supports multi-line messages */
                if (ctl.force_prefix && ctl.method != DMESG_METHOD_KMSG)
                        ctl.force_prefix = 0;
-
                if (ctl.pager)
                        pager_redirect();
                n = read_buffer(&ctl, &buf);
@@ -1601,6 +1647,10 @@ int main(int argc, char *argv[])
                        free(buf);
                if (ctl.kmsg >= 0)
                        close(ctl.kmsg);
+               if (ctl.json && ul_jsonwrt_is_ready(&ctl.jfmt)) {
+                       ul_jsonwrt_array_close(&ctl.jfmt);
+                       ul_jsonwrt_root_close(&ctl.jfmt);
+               }
                if (n < 0)
                        err(EXIT_FAILURE, _("read kernel buffer failed"));
                else if (ctl.action == SYSLOG_ACTION_READ_CLEAR)