recovery shell: print zerrors since the last command was executed

zfsbootmenu/bin/logs

@@ -0,0 +1 @@
+zlogtail

zfsbootmenu/install-helpers.sh

@@ -155,7 +155,8 @@ create_zbm_profiles() {
 	[ -f /etc/profile ] && source /etc/profile
 	[ -f /lib/zfsbootmenu-completions.sh ] && source /lib/zfsbootmenu-completions.sh
 
-	export PS1="\[\033[0;33m\]zfsbootmenu\[\033[0m\] \w > "
+	export PROMPT_COMMAND="/libexec/recovery-error-printer"
+	export PS1='\[\033[0;33m\]zfsbootmenu\[\033[0m\] \w > '
 
 	alias clear="tput clear"
 	alias reset="tput reset"

zfsbootmenu/lib/kmsg-log-lib.sh

@@ -86,6 +86,7 @@ zerror() {
 }
 
 # arg1: comma-separated log levels to print
+# arg2: optional date that messages must be timestamped after
 # prints: all logs at that level
 # returns: nothing
 
@@ -98,14 +99,17 @@ print_kmsg_logs() {
     return
   fi
 
-  # Try to use feature flags found in dmesg from util-linux
-  if output="$( dmesg --notime -f user --color=always -l "${levels}" 2>/dev/null )" ; then
-    echo -e "${output}"
+  since="${2}"
+
+  # dmesg from dmesg-util can helpfully do --since, but only if it's also allowed to print the time out
+  # so always print the time, optionally set --since, and filter the timestamp after
+  if output="$( dmesg -f user --color=never -l "${levels}" ${since:+--since ${since}} 2>/dev/null )" ; then
+    echo "${output}" | sed 's/^\[.*\]\ //'
   else
     # Both util-linux and Busybox dmesg support the -r flag. However, the log level that is
     # reported by Busybox dmesg is larger than that reported by util-linux dmesg. Busybox dmesg
     # is too bare-bones to do much of anything, so we just need to grep for both integers at 
-    # a given log level, then refly on matching ZFSBootMenu for info and lower, and ZBM for debug.
+    # a given log level, then rely on matching ZFSBootMenu for info and lower, and ZBM for debug.
 
     IFS=',' read -r -a levels_array <<<"${levels}"
     for level in "${levels_array[@]}"; do

zfsbootmenu/libexec/recovery-error-printer

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+PROMPT_TS_FILE="${BASE}/.errors_since"
+
+[ -f "${PROMPT_TS_FILE}" ] && read -r prompt_ts < "${PROMPT_TS_FILE}"
+
+# shellcheck disable=SC1091
+source /lib/kmsg-log-lib.sh || exit 0
+
+if [ -f "${BASE}/have_errors" ]; then 
+  echo
+  print_kmsg_logs "err" ${prompt_ts:+${prompt_ts}}
+  echo
+  rm "/zfsbootmenu/have_errors" 
+fi
+
+printf '%(%Y-%m-%dT%H:%M:%S)T' > "${PROMPT_TS_FILE}"