Improved pool imports

1. Allow `zbm.prefer=<pool>!` syntax for a *mandatory* preference; a
   mandatory poll must be imported before other pools will be attempted
   and ZBM continues.

2. Eliminate limits on import retries; the loop will continue
   indefinitely, displaying a countdown that the user can interrupt to
   drop to an emergency shell.

90zfsbootmenu/zfsbootmenu-init.sh

@@ -46,31 +46,21 @@ else
   boot_pool="${root}"
 fi
 
-# Do a dedicated pass for the preferred pool if one was provided
-if [ -n "${boot_pool}" ]; then
-  first_pass=0
-else
-  first_pass=1
-fi
-
+# If a boot pool is specified, that will be tried first
+try_pool="${boot_pool}"
 zbm_import_attempt=0
 while true; do
-  if [ "${first_pass}" -eq 0 ]; then
-    # Try the preferred pool, exactly once
-    zdebug "attempting to import preferred pool ${boot_pool}"
-    try_pool="${boot_pool}"
-  else
-    try_pool=""
+  if [ -n "${try_pool}" ]; then
+    zdebug "attempting to import preferred pool ${try_pool}"
   fi
 
-  first_pass=1
-
   read_write='' import_pool "${try_pool}"
 
   # shellcheck disable=SC2154
   if check_for_pools; then
     if [ -n "${try_pool}" ]; then
-      # If a single pool was requested and imported, try again for the others
+      # If a single pool was requested and imported, try importing others
+      try_pool=""
       continue
     else
       # Otherwise, all possible pools were imported, nothing more to try
@@ -86,25 +76,24 @@ while true; do
     # Store the hostid to use for for KCL overrides
     echo -n "$spl_hostid" > "${BASE}/spl_hostid"
 
-    # Retry the cycle with a matched hostid
+    # If match_hostid succeeds, it has imported *a* pool;
+    # allow another pass to pick up others with the same hostid
+    try_pool=""
     continue
-  elif [ -n "${try_pool}" ]; then
-    # Failure to import a specific pool is not an emergency;
-    # subsequent import passes try all other possible pools
+  elif [ -n "${try_pool}" ] && [ "${zbm_require_bpool:-0}" -ne 1 ]; then
+    # If a specific pool was tried unsuccessfully but is not a requirement,
+    # allow another pass to try any other importable pools
+    try_pool=""
     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="$((zbm_import_attempt + 1))"
+  zbm_import_attempt="$((zbm_import_attempt + 1))"
+  zinfo "unable to import a pool on attempt ${zbm_import_attempt}"
 
-    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
+  # Just keep retrying after a delay until the user presses ESC
+  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

90zfsbootmenu/zfsbootmenu-parse-commandline.sh

@@ -93,20 +93,10 @@ 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
+  info "ZFSBootMenu: import retry delay is ${zbm_import_delay} seconds"
 else
   zbm_import_delay=5
 fi
@@ -196,6 +186,14 @@ case "${root}" in
     ;;
 esac
 
+# Pool preference ending in ! indicates a hard requirement
+bpool="${root%\!}"
+if [ "${bpool}" != "${root}" ]; then
+  # shellcheck disable=SC2034
+  zbm_require_bpool=1
+  root="${bpool}"
+fi
+
 # Make sure Dracut is happy that we have a root
 if [ ${wait_for_zfs} -eq 1 ]; then
   ln -s /dev/null /dev/root 2>/dev/null

90zfsbootmenu/zfsbootmenu-preinit.sh

@@ -30,10 +30,10 @@ export import_policy="${import_policy}"
 export menu_timeout="${menu_timeout}"
 export loglevel="${loglevel}"
 export root="${root}"
+export zbm_require_bpool="${zbm_require_bpool}"
 export zbm_sort="${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"