Support pool import retries

Configurable KCL options provide for a maximum number of retry attempts
(default: 0) and a delay between retries (default: 5s).

90zfsbootmenu/zfsbootmenu-init.sh

@@ -53,6 +53,7 @@ else
   first_pass=1
 fi
 
+zbm_import_attempt=0
 while true; do
   if [ "${first_pass}" -eq 0 ]; then
     # Try the preferred pool, exactly once
@@ -93,6 +94,19 @@ while true; do
     continue
   fi
 
+  if [ "${zbm_import_attempt}" -lt "${zbm_import_retries:-0}" ]; then
+    # The max number of import attempts has not been reached;
+    # retry unless the user decides to abort immediately
+    zbm_import_attempt="$((zbm_import_attempt + 1))"
+
+    zinfo "pool import failed on attempt ${zbm_import_attempt} of ${zbm_import_retries}"
+
+    if delay="${zbm_import_delay:-5}" prompt="Unable to import pool, retrying in %0.2d seconds" \
+        timed_prompt "[RETURN] to retry immediately" "[ESCAPE] for a recovery shell"; then
+      continue
+    fi
+  fi
+
   # Allow the user to attempt recovery
   emergency_shell "unable to successfully import a pool"
 done

90zfsbootmenu/zfsbootmenu-parse-commandline.sh

@@ -93,6 +93,24 @@ else
   menu_timeout=10
 fi
 
+zbm_import_retries=$( getarg zbm.import_retries )
+if [ "${zbm_import_retries:-0}" -gt 0 ] 2>/dev/null ; then 
+  # Beyond logging, this validates that zbm_import_retries is a number
+  info "ZFSBootMenu: will attempt up to ${zbm_import_retries} import retries"
+else
+  zbm_import_retries=0
+fi
+
+zbm_import_delay=$( getarg zbm.import_delay )
+if [ "${zbm_import_delay:-0}" -gt 0 ] 2>/dev/null ; then 
+  # Again, this validates that zbm_import_delay is numeric in addition to logging
+  if [ "${zbm_import_retries}" -gt 0 ]; then
+    info "ZFSBootMenu: import retry delay is ${zbm_import_delay} seconds"
+  fi
+else
+  zbm_import_delay=5
+fi
+
 # Allow setting of console size; there are no defaults here
 # shellcheck disable=SC2034
 zbm_lines=$( getarg zbm.lines=)

90zfsbootmenu/zfsbootmenu-preinit.sh

@@ -32,6 +32,8 @@ export loglevel="${loglevel}"
 export root="${root}"
 export zbm_sort="${zbm_sort}"
 export zbm_set_hostid="${zbm_set_hostid}"
+export zbm_import_delay="${zbm_import_delay}"
+export zbm_import_retries="${zbm_import_retries}"
 EOF
 
 getcmdline > "${BASE}/zbm.cmdline"

man/zfsbootmenu.7

@@ -133,13 +133,13 @@
 .\" ========================================================================
 .\"
 .IX Title "zfsbootmenu 7"
-.TH zfsbootmenu 7 "2021-04-23" "1.9.0" "ZFSBootMenu"
+.TH zfsbootmenu 7 "2021-06-03" "1.9.0" "ZFSBootMenu"
 .\" For nroff, turn off justification.  Always turn off hyphenation; it makes
 .\" way too many mistakes in technical documents.
 .if n .ad l
 .nh
 .SH "NAME"
-zfsbootmenu \- System integration
+zfsbootmenu \- System Integration
 .SH "SYNOPSIS"
 .IX Header "SYNOPSIS"
 ZFSBootMenu behavior is controlled through \s-1ZFS\s0 filesystem properties and command-line options provided to the ZFSBootMenu kernel.
@@ -152,6 +152,12 @@ When creating an initramfs or \s-1UEFI\s0 bundle, the \fI/etc/hostid\fR from the
 .IP "\fBzbm.prefer=<pool>\fR" 4
 .IX Item "zbm.prefer=<pool>"
 By default, ZFSBootMenu will look for the \fIbootfs\fR property on the first imported pool (sorted alphabetically) to select the default boot environment. If you have multiple pools, replace \fB<pool>\fR with the name of your preferred pool to override the default.
+.IP "\fBzbm.import_retries=<count>\fR" 4
+.IX Item "zbm.import_retries=<count>"
+If ZFSBootMenu fails to import a pool and \fB<count>\fR is a positive integer, the import will be attempted up to \fB<count>\fR times before dropping to an emergency shell to facilitate recovery. By default or if \fB<count>\fR is anything besides a positive integer, imports will not be retried.
+.IP "\fBzbm.import_delay=<time>\fR" 4
+.IX Item "zbm.import_delay=<time>"
+If ZFSBootMenu is configured to retry imports via \fBzbm.import_retries\fR, each retried attempt will proceed after a delay of \fB<time>\fR seconds. When \fB<time>\fR is unspecified or is anything other than a positive integer, a default value of 5 seconds will be used.
 .IP "\fBzbm.import_policy\fR" 4
 .IX Item "zbm.import_policy"
 This option controls how the pool import process should take place.

pod/zfsbootmenu.7.pod

@@ -22,6 +22,14 @@ When creating an initramfs or UEFI bundle, the I</etc/hostid> from the system is
 
 By default, ZFSBootMenu will look for the I<bootfs> property on the first imported pool (sorted alphabetically) to select the default boot environment. If you have multiple pools, replace B<E<lt>poolE<gt>> with the name of your preferred pool to override the default.
 
+=item B<zbm.import_retries=E<lt>countE<gt>>
+
+If ZFSBootMenu fails to import a pool and B<E<lt>countE<gt>> is a positive integer, the import will be attempted up to B<E<lt>countE<gt>> times before dropping to an emergency shell to facilitate recovery. By default or if B<E<lt>countE<gt>> is anything besides a positive integer, imports will not be retried.
+
+=item B<zbm.import_delay=E<lt>timeE<gt>>
+
+If ZFSBootMenu is configured to retry imports via B<zbm.import_retries>, each retried attempt will proceed after a delay of B<E<lt>timeE<gt>> seconds. When B<E<lt>timeE<gt>> is unspecified or is anything other than a positive integer, a default value of 5 seconds will be used.
+
 =item B<zbm.import_policy>
 
 This option controls how the pool import process should take place.