journalctl: augment short mode with a cursor at the end

Two options are added: --show-cursor to print the cursor at the end,
and --after-cursor to resume logs on the next line after the previous one.

3 files changed, 129 insertions, 90 deletions

diff --git a/TODO b/TODO
index 902fbc695e..06771d5bf5 100644
--- a/TODO
+++ b/TODO
@@ -64,8 +64,6 @@ Features:
 
 * when parsing calendar timestamps support the UTC timezone (even if we won't support arbitrary timezone specs, support UTC itself certainly makes sense), also support syntaxes such as +0200
 
-* journalctl: add an output mode that looks like classic /var/log/messages, but also outputs the cursor of the last entry so that people can write scripts that can run iteratively and always process data that has been added since the last time.
-
 * when a kernel driver logs in a tight loop we should ratelimit that too.
 
 * man: document in the journalctl man page what the colors mean
diff --git a/man/journalctl.xml b/man/journalctl.xml
index 027f22d259..3e03c45f13 100644
--- a/man/journalctl.xml
+++ b/man/journalctl.xml
@@ -523,6 +523,16 @@
                         </varlistentry>
 
                         <varlistentry>
+                                <term><option>--after-cursor=</option></term>
+
+                                <listitem><para>Start showing entries from the
+                                location in the journal
+                                <emphasis>after</emphasis> the location
+                                specified by the this cursor.
+                                </para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
                                 <term><option>--since=</option></term>
                                 <term><option>--until=</option></term>
 
diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index 38b2cdd572..7415abc74f 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -74,6 +74,8 @@ static bool arg_boot_id = false;
 static char *arg_boot_id_descriptor = NULL;
 static bool arg_dmesg = false;
 static const char *arg_cursor = NULL;
+static const char *arg_after_cursor = NULL;
+static bool arg_show_cursor = false;
 static const char *arg_directory = NULL;
 static char **arg_file = NULL;
 static int arg_priorities = 0xFF;
@@ -114,50 +116,52 @@ static int help(void) {
         printf("%s [OPTIONS...] [MATCHES...]\n\n"
                "Query the journal.\n\n"
                "Flags:\n"
-               "     --system            Show only the system journal\n"
-               "     --user              Show only the user journal for current user\n"
-               "     --since=DATE        Start showing entries newer or of the specified date\n"
-               "     --until=DATE        Stop showing entries older or of the specified date\n"
-               "  -c --cursor=CURSOR     Start showing entries from specified cursor\n"
-               "  -b --boot[=ID]         Show data only from ID or current boot if unspecified\n"
-               "  -k --dmesg             Show kernel message log from current boot\n"
-               "  -u --unit=UNIT         Show data only from the specified unit\n"
-               "     --user-unit=UNIT    Show data only from the specified user session unit\n"
-               "  -p --priority=RANGE    Show only messages within the specified priority range\n"
-               "  -e --pager-end         Immediately jump to end of the journal in the pager\n"
-               "  -f --follow            Follow journal\n"
-               "  -n --lines[=INTEGER]   Number of journal entries to show\n"
-               "     --no-tail           Show all lines, even in follow mode\n"
-               "  -r --reverse           Show the newest entries first\n"
-               "  -o --output=STRING     Change journal output mode (short, short-monotonic,\n"
-               "                         verbose, export, json, json-pretty, json-sse, cat)\n"
-               "  -x --catalog           Add message explanations where available\n"
-               "  -l --full              Do not ellipsize fields\n"
-               "  -a --all               Show all fields, including long and unprintable\n"
-               "  -q --quiet             Don't show privilege warning\n"
-               "     --no-pager          Do not pipe output into a pager\n"
-               "  -m --merge             Show entries from all available journals\n"
-               "  -D --directory=PATH    Show journal files from directory\n"
-               "     --file=PATH         Show journal file\n"
-               "     --root=ROOT         Operate on catalog files underneath the root ROOT\n"
+               "     --system              Show only the system journal\n"
+               "     --user                Show only the user journal for current user\n"
+               "     --since=DATE          Start showing entries newer or of the specified date\n"
+               "     --until=DATE          Stop showing entries older or of the specified date\n"
+               "  -c --cursor=CURSOR       Start showing entries from specified cursor\n"
+               "     --after-cursor=CURSOR Start showing entries from specified cursor\n"
+               "     --show-cursor         Print the cursor after all the entries\n"
+               "  -b --boot[=ID]           Show data only from ID or current boot if unspecified\n"
+               "  -k --dmesg               Show kernel message log from current boot\n"
+               "  -u --unit=UNIT           Show data only from the specified unit\n"
+               "     --user-unit=UNIT      Show data only from the specified user session unit\n"
+               "  -p --priority=RANGE      Show only messages within the specified priority range\n"
+               "  -e --pager-end           Immediately jump to end of the journal in the pager\n"
+               "  -f --follow              Follow journal\n"
+               "  -n --lines[=INTEGER]     Number of journal entries to show\n"
+               "     --no-tail             Show all lines, even in follow mode\n"
+               "  -r --reverse             Show the newest entries first\n"
+               "  -o --output=STRING       Change journal output mode (short, short-monotonic,\n"
+               "                           verbose, export, json, json-pretty, json-sse, cat)\n"
+               "  -x --catalog             Add message explanations where available\n"
+               "  -l --full                Do not ellipsize fields\n"
+               "  -a --all                 Show all fields, including long and unprintable\n"
+               "  -q --quiet               Don't show privilege warning\n"
+               "     --no-pager            Do not pipe output into a pager\n"
+               "  -m --merge               Show entries from all available journals\n"
+               "  -D --directory=PATH      Show journal files from directory\n"
+               "     --file=PATH           Show journal file\n"
+               "     --root=ROOT           Operate on catalog files underneath the root ROOT\n"
 #ifdef HAVE_GCRYPT
-               "     --interval=TIME     Time interval for changing the FSS sealing key\n"
-               "     --verify-key=KEY    Specify FSS verification key\n"
+               "     --interval=TIME       Time interval for changing the FSS sealing key\n"
+               "     --verify-key=KEY      Specify FSS verification key\n"
+               "     --force               Force overriding new FSS key pair with --setup-keys\n"
 #endif
                "\nCommands:\n"
-               "  -h --help              Show this help\n"
-               "     --version           Show package version\n"
-               "     --new-id128         Generate a new 128 Bit ID\n"
-               "     --header            Show journal header information\n"
-               "     --disk-usage        Show total disk usage\n"
-               "  -F --field=FIELD       List all values a certain field takes\n"
-               "     --list-catalog      Show message IDs of all entries in the message catalog\n"
-               "     --dump-catalog      Show entries in the message catalog\n"
-               "     --update-catalog    Update the message catalog database\n"
+               "  -h --help                Show this help\n"
+               "     --version             Show package version\n"
+               "     --new-id128           Generate a new 128 Bit ID\n"
+               "     --header              Show journal header information\n"
+               "     --disk-usage          Show total disk usage\n"
+               "  -F --field=FIELD         List all values a certain field takes\n"
+               "     --list-catalog        Show message IDs of all entries in the message catalog\n"
+               "     --dump-catalog        Show entries in the message catalog\n"
+               "     --update-catalog      Update the message catalog database\n"
 #ifdef HAVE_GCRYPT
-               "     --setup-keys        Generate new FSS key pair\n"
-               "     --force             Force overriding new FSS key pair with --setup-keys\n"
-               "     --verify            Verify journal file consistency\n"
+               "     --setup-keys          Generate new FSS key pair\n"
+               "     --verify              Verify journal file consistency\n"
 #endif
                , program_invocation_short_name);
 
@@ -183,6 +187,8 @@ static int parse_argv(int argc, char *argv[]) {
                 ARG_DISK_USAGE,
                 ARG_SINCE,
                 ARG_UNTIL,
+                ARG_AFTER_CURSOR,
+                ARG_SHOW_CURSOR,
                 ARG_USER_UNIT,
                 ARG_LIST_CATALOG,
                 ARG_DUMP_CATALOG,
@@ -191,47 +197,49 @@ static int parse_argv(int argc, char *argv[]) {
         };
 
         static const struct option options[] = {
-                { "help",         no_argument,       NULL, 'h'              },
-                { "version" ,     no_argument,       NULL, ARG_VERSION      },
-                { "no-pager",     no_argument,       NULL, ARG_NO_PAGER     },
-                { "pager-end",    no_argument,       NULL, 'e'              },
-                { "follow",       no_argument,       NULL, 'f'              },
-                { "force",        no_argument,       NULL, ARG_FORCE        },
-                { "output",       required_argument, NULL, 'o'              },
-                { "all",          no_argument,       NULL, 'a'              },
-                { "full",         no_argument,       NULL, 'l'              },
-                { "lines",        optional_argument, NULL, 'n'              },
-                { "no-tail",      no_argument,       NULL, ARG_NO_TAIL      },
-                { "new-id128",    no_argument,       NULL, ARG_NEW_ID128    },
-                { "quiet",        no_argument,       NULL, 'q'              },
-                { "merge",        no_argument,       NULL, 'm'              },
-                { "boot",         optional_argument, NULL, 'b'              },
-                { "this-boot",    optional_argument, NULL, 'b'              }, /* deprecated */
-                { "dmesg",        no_argument,       NULL, 'k'              },
-                { "system",       no_argument,       NULL, ARG_SYSTEM       },
-                { "user",         no_argument,       NULL, ARG_USER         },
-                { "directory",    required_argument, NULL, 'D'              },
-                { "file",         required_argument, NULL, ARG_FILE         },
-                { "root",         required_argument, NULL, ARG_ROOT         },
-                { "header",       no_argument,       NULL, ARG_HEADER       },
-                { "priority",     required_argument, NULL, 'p'              },
-                { "setup-keys",   no_argument,       NULL, ARG_SETUP_KEYS   },
-                { "interval",     required_argument, NULL, ARG_INTERVAL     },
-                { "verify",       no_argument,       NULL, ARG_VERIFY       },
-                { "verify-key",   required_argument, NULL, ARG_VERIFY_KEY   },
-                { "disk-usage",   no_argument,       NULL, ARG_DISK_USAGE   },
-                { "cursor",       required_argument, NULL, 'c'              },
-                { "since",        required_argument, NULL, ARG_SINCE        },
-                { "until",        required_argument, NULL, ARG_UNTIL        },
-                { "unit",         required_argument, NULL, 'u'              },
-                { "user-unit",    required_argument, NULL, ARG_USER_UNIT    },
-                { "field",        required_argument, NULL, 'F'              },
-                { "catalog",      no_argument,       NULL, 'x'              },
-                { "list-catalog", no_argument,       NULL, ARG_LIST_CATALOG },
-                { "dump-catalog", no_argument,       NULL, ARG_DUMP_CATALOG },
-                { "update-catalog",no_argument,      NULL, ARG_UPDATE_CATALOG },
-                { "reverse",      no_argument,       NULL, 'r'              },
-                { NULL,           0,                 NULL, 0                }
+                { "help",           no_argument,       NULL, 'h'                },
+                { "version" ,       no_argument,       NULL, ARG_VERSION        },
+                { "no-pager",       no_argument,       NULL, ARG_NO_PAGER       },
+                { "pager-end",      no_argument,       NULL, 'e'                },
+                { "follow",         no_argument,       NULL, 'f'                },
+                { "force",          no_argument,       NULL, ARG_FORCE          },
+                { "output",         required_argument, NULL, 'o'                },
+                { "all",            no_argument,       NULL, 'a'                },
+                { "full",           no_argument,       NULL, 'l'                },
+                { "lines",          optional_argument, NULL, 'n'                },
+                { "no-tail",        no_argument,       NULL, ARG_NO_TAIL        },
+                { "new-id128",      no_argument,       NULL, ARG_NEW_ID128      },
+                { "quiet",          no_argument,       NULL, 'q'                },
+                { "merge",          no_argument,       NULL, 'm'                },
+                { "boot",           optional_argument, NULL, 'b'                },
+                { "this-boot",      optional_argument, NULL, 'b'                }, /* deprecated */
+                { "dmesg",          no_argument,       NULL, 'k'                },
+                { "system",         no_argument,       NULL, ARG_SYSTEM         },
+                { "user",           no_argument,       NULL, ARG_USER           },
+                { "directory",      required_argument, NULL, 'D'                },
+                { "file",           required_argument, NULL, ARG_FILE           },
+                { "root",           required_argument, NULL, ARG_ROOT           },
+                { "header",         no_argument,       NULL, ARG_HEADER         },
+                { "priority",       required_argument, NULL, 'p'                },
+                { "setup-keys",     no_argument,       NULL, ARG_SETUP_KEYS     },
+                { "interval",       required_argument, NULL, ARG_INTERVAL       },
+                { "verify",         no_argument,       NULL, ARG_VERIFY         },
+                { "verify-key",     required_argument, NULL, ARG_VERIFY_KEY     },
+                { "disk-usage",     no_argument,       NULL, ARG_DISK_USAGE     },
+                { "cursor",         required_argument, NULL, 'c'                },
+                { "after-cursor",   required_argument, NULL, ARG_AFTER_CURSOR   },
+                { "show-cursor",    no_argument,       NULL, ARG_SHOW_CURSOR    },
+                { "since",          required_argument, NULL, ARG_SINCE          },
+                { "until",          required_argument, NULL, ARG_UNTIL          },
+                { "unit",           required_argument, NULL, 'u'                },
+                { "user-unit",      required_argument, NULL, ARG_USER_UNIT      },
+                { "field",          required_argument, NULL, 'F'                },
+                { "catalog",        no_argument,       NULL, 'x'                },
+                { "list-catalog",   no_argument,       NULL, ARG_LIST_CATALOG   },
+                { "dump-catalog",   no_argument,       NULL, ARG_DUMP_CATALOG   },
+                { "update-catalog", no_argument,       NULL, ARG_UPDATE_CATALOG },
+                { "reverse",        no_argument,       NULL, 'r'                },
+                { NULL,             0,                 NULL, 0                  }
         };
 
         int c, r;
@@ -379,6 +387,14 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_cursor = optarg;
                         break;
 
+                case ARG_AFTER_CURSOR:
+                        arg_after_cursor = optarg;
+                        break;
+
+                case ARG_SHOW_CURSOR:
+                        arg_show_cursor = true;
+                        break;
+
                 case ARG_HEADER:
                         arg_action = ACTION_PRINT_HEADER;
                         break;
@@ -549,8 +565,8 @@ static int parse_argv(int argc, char *argv[]) {
                 return -EINVAL;
         }
 
-        if (arg_cursor && arg_since_set) {
-                log_error("Please specify either --since= or --cursor=, not both.");
+        if (!!arg_cursor + !!arg_after_cursor + !!arg_since_set > 1) {
+                log_error("Please specify only one of --since=, --cursor=, and --after-cursor.");
                 return -EINVAL;
         }
 
@@ -1435,16 +1451,20 @@ int main(int argc, char *argv[]) {
                         return EXIT_FAILURE;
         }
 
-        if (arg_cursor) {
-                r = sd_journal_seek_cursor(j, arg_cursor);
+        if (arg_cursor || arg_after_cursor) {
+                r = sd_journal_seek_cursor(j, arg_cursor ? arg_cursor : arg_after_cursor);
                 if (r < 0) {
                         log_error("Failed to seek to cursor: %s", strerror(-r));
                         return EXIT_FAILURE;
                 }
                 if (!arg_reverse)
-                        r = sd_journal_next(j);
+                        r = sd_journal_next_skip(j, 1 + !!arg_after_cursor);
                 else
-                        r = sd_journal_previous(j);
+                        r = sd_journal_previous_skip(j, 1 + !!arg_after_cursor);
+
+                if (arg_after_cursor && r < 2 && !arg_follow)
+                        /* We couldn't find the next entry after the cursor. */
+                        arg_lines = 0;
 
         } else if (arg_since_set && !arg_reverse) {
                 r = sd_journal_seek_realtime_usec(j, arg_since);
@@ -1592,8 +1612,19 @@ int main(int argc, char *argv[]) {
                         n_shown++;
                 }
 
-                if (!arg_follow)
+                if (!arg_follow) {
+                        if (arg_show_cursor) {
+                                _cleanup_free_ char *cursor = NULL;
+
+                                r = sd_journal_get_cursor(j, &cursor);
+                                if (r < 0 && r != -EADDRNOTAVAIL)
+                                        log_error("Failed to get cursor: %s", strerror(-r));
+                                else if (r >= 0)
+                                        printf("-- cursor: %s\n", cursor);
+                        }
+
                         break;
+                }
 
                 r = sd_journal_wait(j, (uint64_t) -1);
                 if (r < 0) {