journalctl: remove ":" from the --boot syntax

Instead of :-0, :1, :5, etc., use -0, 1 or +1, 5, etc. For BOOT_ID+OFFSET,
use BOOT_ID+offset or BOOT_ID-offset (either + or - is required).

Also make error handling a bit more robust and verbose.
Modify the man page to describe the most common case (-b) first,
and the second most common case (-b -1) second.

2 files changed, 121 insertions, 117 deletions

diff --git a/man/journalctl.xml b/man/journalctl.xml
index 3e03c45f13..65a59ea4e7 100644
--- a/man/journalctl.xml
+++ b/man/journalctl.xml
@@ -399,42 +399,50 @@
                         </varlistentry>
 
                         <varlistentry>
-                                <term><option>-b <optional><replaceable>ID</replaceable></optional></option></term>
-                                <term><option>--boot=<optional><replaceable>ID</replaceable></optional></option></term>
+                                <term><option>-b <optional><replaceable>ID</replaceable></optional><optional><replaceable>±offset</replaceable></optional></option></term>
+                                <term><option>--boot=<optional><replaceable>ID</replaceable></optional><optional><replaceable>±offset</replaceable></optional></option></term>
 
-                                <listitem><para>Show messages from the specified
-                                boot <replaceable>ID</replaceable> or from
-                                current boot if no <replaceable>ID</replaceable>
-                                is given. This will add a match for
+                                <listitem><para>Show messages from a specific
+                                boot. This will add a match for
                                 <literal>_BOOT_ID=</literal>.</para>
 
-                                <para>The argument is a 128 bit ID given in
-                                short or UUID form and optionally followed by
-                                <literal>:n</literal> which identifies the nth
-                                boot relative to the boot ID given to the left
-                                of <literal>:</literal>. Supplying a negative
-                                value for n will look for a past boot and a
-                                positive value for a future boot. The boot IDs
-                                are searched for in chronological order. If no
-                                number is provided after <literal>:</literal>,
-                                <literal>-1</literal> is assumed. A value of 0
-                                is valid and equivalent to omitting
-                                <literal>:0</literal>.</para>
-
-                                <para>Alternatively, the argument may constist
-                                only of <literal>:n</literal>. In this case, a
-                                positive value will look up the nth boot
-                                starting from the beginning of the jouranl, a
-                                negative value will look up a previous boot
-                                relative to the current boot. <literal>:0</literal>
-                                will look for the current boot ID. Thus,
-                                <literal>:1</literal> is the first boot found in
-                                the journal, <literal>:2</literal> the second
-                                and so on; while <literal>:-1</literal> is the
-                                previous boot, <literal>:-2</literal> the boot
-                                before that and so on. Omitting a value after
-                                <literal>:</literal> will look for the previous
-                                boot.</para></listitem>
+                                <para>The argument may be empty, in which case
+                                logs for the current boot will be shown.</para>
+
+                                <para>If the boot ID is omitted, a positive
+                                <replaceable>offset</replaceable> will look up
+                                the boots starting from the beginning of the
+                                journal, and a equal-or-less-than zero
+                                <replaceable>offset</replaceable> will look up
+                                boots starting from the end of the
+                                journal. Thus, <constant>1</constant> means the
+                                first boot found in the journal in the
+                                chronological order, <constant>2</constant> the
+                                second and so on; while <constant>-0</constant>
+                                is the last boot, <constant>-1</constant> the
+                                boot before that, and so on. An empty
+                                <replaceable>offset</replaceable> is equivalent
+                                to specifying <constant>-0</constant>, except
+                                when the current boot is not the last boot
+                                (e.g. because <option>--directory</option> was
+                                specified to look at logs from a different
+                                machine).</para>
+
+                                <para>If the 32 character
+                                <replaceable>ID</replaceable> is specified, it
+                                may optionally be followed by
+                                <replaceable>offset</replaceable> which
+                                identifies the boot relative to the one given by
+                                boot <replaceable>ID</replaceable>. Negative
+                                values mean earlier boots and a positive values
+                                mean later boots. If
+                                <replaceable>offset</replaceable> is not
+                                specified, a value of zero is assumed and the
+                                logs for the boot given by
+                                <replaceable>ID</replaceable> are shown.
+                                </para>
+
+                                </listitem>
                         </varlistentry>
 
                         <varlistentry>
diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index 7099706696..9a40d69a75 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -70,8 +70,8 @@ static int arg_lines = -1;
 static bool arg_no_tail = false;
 static bool arg_quiet = false;
 static bool arg_merge = false;
-static bool arg_boot_id = false;
-static char *arg_boot_id_descriptor = NULL;
+static bool arg_boot = false;
+static char *arg_boot_descriptor = NULL;
 static bool arg_dmesg = false;
 static const char *arg_cursor = NULL;
 static const char *arg_after_cursor = NULL;
@@ -346,17 +346,24 @@ static int parse_argv(int argc, char *argv[]) {
                         break;
 
                 case 'b':
+                        arg_boot = true;
+
                         if (optarg)
-                                arg_boot_id_descriptor = optarg;
-                        else if (optind < argc && argv[optind][0] != '-') {
-                                arg_boot_id_descriptor = argv[optind];
-                                optind++;
+                                arg_boot_descriptor = optarg;
+                        else if (optind < argc) {
+                                int boot;
+
+                                if (argv[optind][0] != '-' ||
+                                    safe_atoi(argv[optind], &boot) >= 0) {
+                                        arg_boot_descriptor = argv[optind];
+                                        optind++;
+                                }
                         }
-                        arg_boot_id = true;
+
                         break;
 
                 case 'k':
-                        arg_boot_id = arg_dmesg = true;
+                        arg_boot = arg_dmesg = true;
                         break;
 
                 case ARG_SYSTEM:
@@ -671,23 +678,17 @@ static int boot_id_cmp(const void *a, const void *b) {
 static int get_relative_boot_id(sd_journal *j, sd_id128_t *boot_id, int relative) {
         int r;
         const void *data;
-        unsigned int id_count = 0;
+        unsigned int count = 0;
         size_t length, allocated = 0;
-        boot_id_t ref_boot_id, *id;
+        boot_id_t ref_boot_id = {SD_ID128_NULL}, *id;
         _cleanup_free_ boot_id_t *all_ids = NULL;
-        bool find_first_boot = false, ref_boot_found = false;
 
         assert(j);
         assert(boot_id);
 
-        if (relative == 0)
+        if (relative == 0 && !sd_id128_equal(*boot_id, SD_ID128_NULL))
                 return 0;
 
-        if (sd_id128_equal(*boot_id, SD_ID128_NULL) && relative > 0) {
-                find_first_boot = true;
-                relative--;
-        }
-
         r = sd_journal_query_unique(j, "_BOOT_ID");
         if (r < 0)
                 return r;
@@ -696,123 +697,118 @@ static int get_relative_boot_id(sd_journal *j, sd_id128_t *boot_id, int relative
                 if (length < strlen("_BOOT_ID="))
                         continue;
 
-                if (!GREEDY_REALLOC(all_ids, allocated, id_count + 1))
+                if (!GREEDY_REALLOC(all_ids, allocated, count + 1))
                         return log_oom();
 
-                id = &all_ids[id_count];
+                id = &all_ids[count];
 
                 r = sd_id128_from_string(((const char *)data) + strlen("_BOOT_ID="), &id->id);
-                if (r < 0) {
+                if (r < 0)
                         continue;
-                }
 
-                sd_journal_flush_matches(j);
                 r = sd_journal_add_match(j, data, length);
                 if (r < 0)
-                        continue;
+                        return r;
 
                 r = sd_journal_seek_head(j);
                 if (r < 0)
-                        continue;
+                        return r;
 
                 r = sd_journal_next(j);
-                if (r <= 0)
-                        continue;
+                if (r < 0)
+                        return r;
+                else if (r == 0)
+                        goto flush;
 
                 r = sd_journal_get_realtime_usec(j, &id->timestamp);
                 if (r < 0)
-                        continue;
+                        return r;
 
-                if (!find_first_boot && sd_id128_equal(id->id, *boot_id)) {
+                if (sd_id128_equal(id->id, *boot_id))
                         ref_boot_id = *id;
-                        ref_boot_found = true;
-                }
 
-                id_count++;
+                count++;
+        flush:
+                sd_journal_flush_matches(j);
         }
 
-        *boot_id = SD_ID128_NULL;
-        sd_journal_flush_matches(j);
+        qsort(all_ids, count, sizeof(boot_id_t), boot_id_cmp);
 
-        if (id_count == 0 || (!find_first_boot && !ref_boot_found))
-                return 0;
+        if (sd_id128_equal(*boot_id, SD_ID128_NULL)) {
+                if (relative > (int) count || relative <= -(int)count)
+                        return -EADDRNOTAVAIL;
 
-        qsort(all_ids, id_count, sizeof(boot_id_t), boot_id_cmp);
-        if (find_first_boot)
-                id = all_ids;
-        else
-                id = bsearch(&ref_boot_id, all_ids, id_count, sizeof(boot_id_t), boot_id_cmp);
+                *boot_id = all_ids[(relative <= 0)*count + relative - 1].id;
+        } else {
+                id = bsearch(&ref_boot_id, all_ids, count, sizeof(boot_id_t), boot_id_cmp);
 
-        if (!id || (relative < 0 && ((id - all_ids) + relative) < 0) ||
-            (relative >= 0 && (unsigned long)((id - all_ids) + relative) >= id_count))
-                return 0;
+                if (!id ||
+                    relative <= 0 ? (id - all_ids) + relative < 0 :
+                                    (id - all_ids) + relative >= count)
+                        return -EADDRNOTAVAIL;
+
+                *boot_id = (id + relative)->id;
+        }
 
-        id += relative;
-        *boot_id = id->id;
         return 0;
 }
 
 static int add_boot(sd_journal *j) {
         char match[9+32+1] = "_BOOT_ID=";
-        char *marker;
-        sd_id128_t boot_id;
+        char *offset;
+        sd_id128_t boot_id = SD_ID128_NULL;
         int r, relative = 0;
 
         assert(j);
 
-        if (!arg_boot_id)
+        if (!arg_boot)
                 return 0;
 
-        if (arg_boot_id_descriptor) {
-                marker = strchr(arg_boot_id_descriptor, ':');
-                if (marker) {
-                        *marker = '\0';
-                        marker++;
+        if (!arg_boot_descriptor)
+                return add_match_this_boot(j);
 
-                        if (*marker == '\0')
-                                relative = -1;
-                        else {
-                                r = safe_atoi(marker, &relative);
-                                if (r < 0) {
-                                        log_error("Failed to parse relative boot ID number '%s'", marker);
-                                        return -EINVAL;
-                                }
-                        }
+        if (strlen(arg_boot_descriptor) >= 32) {
+                char tmp = arg_boot_descriptor[32];
+                arg_boot_descriptor[32] = '\0';
+                r = sd_id128_from_string(arg_boot_descriptor, &boot_id);
+                arg_boot_descriptor[32] = tmp;
+
+                if (r < 0) {
+                        log_error("Failed to parse boot ID '%.32s': %s",
+                                  arg_boot_descriptor, strerror(-r));
+                        return r;
                 }
-        }
 
-        if (isempty(arg_boot_id_descriptor)) {
-                if (relative > 0) {
-                        /* We cannot look into the future. Instead, we look
-                         * into the past (starting from first boot). The ID
-                         * will be looked up later */
-                        boot_id = SD_ID128_NULL;
-                } else {
-                        r = sd_id128_get_boot(&boot_id);
-                        if (r < 0) {
-                                log_error("Failed to get boot ID: %s", strerror(-r));
-                                return r;
-                        }
+                offset = arg_boot_descriptor + 32;
+
+                if (*offset != '-' && *offset != '+') {
+                        log_error("Relative boot ID offset must start with a '+' or a '-', found '%s' ", offset);
+                        return -EINVAL;
                 }
-        } else {
-                r = sd_id128_from_string(arg_boot_id_descriptor, &boot_id);
+        } else
+                offset = arg_boot_descriptor;
+
+        if (*offset) {
+                r = safe_atoi(offset, &relative);
                 if (r < 0) {
-                        log_error("Failed to parse boot ID: %s", strerror(-r));
-                        return r;
+                        log_error("Failed to parse relative boot ID number '%s'", offset);
+                        return -EINVAL;
                 }
         }
 
         r = get_relative_boot_id(j, &boot_id, relative);
         if (r < 0) {
-                log_error("Failed to look up boot ID: %s", strerror(-r));
+                if (sd_id128_equal(boot_id, SD_ID128_NULL))
+                        log_error("Failed to look up boot %+d: %s", relative, strerror(-r));
+                else
+                        log_error("Failed to look up boot ID "SD_ID128_FORMAT_STR"%+d: %s",
+                                  SD_ID128_FORMAT_VAL(boot_id), relative, strerror(-r));
                 return r;
-        } else if (sd_id128_equal(boot_id, SD_ID128_NULL)) {
-                log_error("Failed to find boot ID");
-                return -1;
         }
 
         sd_id128_to_string(boot_id, match + 9);
-        r = sd_journal_add_match(j, match, strlen(match));
+
+        r = sd_journal_add_match(j, match, sizeof(match) - 1);
         if (r < 0) {
                 log_error("Failed to add match: %s", strerror(-r));
                 return r;