nfs_server as new restore method

doc/rear.8.adoc

@@ -366,6 +366,11 @@ Use BorgBackup (short Borg) a deduplicating backup program to restore the data.
 Executing 'rear mkbackup' will create a Borg backup,
 see the section 'ReaR with Borg back end' in the ReaR user-guide 'Scenarios' documentation.
 
+BACKUP=*NFS4SERVER*::
+This is a restore only method. ReaR starts a NFSv4 server in the restore stage and
+provides the to be restored filesystems as NFSv4 share. Another
+server (with a special backup sotware) can mount this share and can push the backup data into it.
+
 The following +BACKUP+ methods are _internal_ of Relax-and-Recover:
 
 BACKUP=*NETFS*::

usr/share/rear/conf/default.conf

@@ -2169,6 +2169,28 @@ COPY_AS_IS_NBKDC=()
 COPY_AS_IS_EXCLUDE_NBKDC=()
 ####
 
+####
+# BACKUP=NFS4SERVER
+##
+# Note: This is for restore via NFS server, where another computer can connect to the rescue system via NFS and push
+#       the backup files onto the disks after ReaR prepared and formatted them.
+#
+#       This method has no backup functionality, only restore. And it requires interaction with an external system to push the files.
+#
+#       ReaR will wait for a signal file to appear to indicate that the file transfer is complete.
+#
+REQUIRED_PROGS_NFS4SERVER=("rpc.nfsd" "rpc.mountd" "exportfs" "ss" "nproc")
+NFS4SERVER_MODULES=(nfs nfsd)
+# List of share options for the recovery system, see 'General Options' in exports(5)
+NFS4SERVER_EXPORT_OPTS=(rw no_root_squash async no_subtree_check)
+# List of trusted systems that can mount the recovery system, see 'Machine Name Formats' in exports(5)
+# e.g. NFS4SERVER_TRUSTED_CLIENTS=( myclient 172.16.76.0/24 )
+NFS4SERVER_TRUSTED_CLIENTS=()
+# this file is relative to $TARGET_FS_ROOT/
+# it will be deleted after restore
+NFS4SERVER_RESTORE_FINISHED_FILE=var/lib/rear/rear_finished.txt
+
+
 ####
 # BACKUP=GALAXY
 ##

usr/share/rear/prep/NFS4SERVER/default/400_prep_nfs_server.sh

@@ -0,0 +1,13 @@
+# 400_prep_nfs_server.sh
+#
+# prepare stuff for NFS4SERVER
+#
+
+PROGS+=("${PROGS_NFS4SERVER[@]}")
+
+REQUIRED_PROGS+=("${REQUIRED_PROGS_NFS4SERVER[@]}")
+
+MODULES_LOAD+=("${NFS4SERVER_MODULES[@]}")
+
+# Check if at least one trusted client was specified
+(( "${#NFS4SERVER_TRUSTED_CLIENTS[@]}" > 0 )) || Error "You must have defined at least one client in NFS4SERVER_TRUSTED_CLIENTS."

usr/share/rear/restore/NFS4SERVER/default/300_start_nfs_server.sh

@@ -0,0 +1,42 @@
+# 300_start_nfs_server.sh
+
+# same options works for mountd
+local nfsd_opts=(--no-udp --no-nfs-version 3 -V 4.2)
+local cpu_cores
+cpu_cores=$(nproc) || Error "Could not determine CPU details via nproc"
+# 4 threads per cpu core
+local nfs_threads=$(( $cpu_cores * 4 ))
+# 8 are the standard and should be the minumun
+if (( nfs_threads < 8 )); then nfs_threads=8; fi
+
+# clear /etc/exports if the user rerun the restore with other options
+> /etc/exports
+
+# add all mountpoints to /etc/exports
+while read mountpoint junk ; do
+    local options=("${NFS4SERVER_EXPORT_OPTS[@]}")
+    if [[ $mountpoint == "/" ]]; then
+        options+=("fsid=0")
+    else
+        options+=(nohide)
+    fi
+    local nfs_options=$(IFS=',' ; echo "${options[*]}")
+    local nfs_trust_options=""
+    for trust in "${NFS4SERVER_TRUSTED_CLIENTS[@]}"; do
+        nfs_trust_options+="$trust($nfs_options) "
+    done
+
+    echo "${TARGET_FS_ROOT}${mountpoint} $nfs_trust_options" >> /etc/exports
+done < "${VAR_DIR}/recovery/mountpoint_device"
+Debug "$(cat /etc/exports)"
+
+exportfs $v -ra || Error "exportfs failed!"
+
+rpc.nfsd --debug "$nfs_threads" "${nfsd_opts[@]}" || Error "rpc.nfsd failed!"
+Debug "nfsd startet with $nfs_threads threads."
+
+if [ -z "$(pidof rpc.mountd)" ]; then
+    rpc.mountd --debug all "${nfsd_opts[@]}" || Error "rpc.mountd failed!"
+fi
+
+LogPrint "NFS-Server started successfully."

usr/share/rear/restore/NFS4SERVER/default/400_restore_with_nfs_server.sh

@@ -0,0 +1,23 @@
+# 400_restore_with_nfs_server.sh
+
+local check_file="$TARGET_FS_ROOT/$NFS4SERVER_RESTORE_FINISHED_FILE"
+
+LogPrint "Mount the nfs share: 'mount -t nfs <ip>:/ <destination>' and restore all files to mounted destination."
+LogPrint "Create the $check_file file when the restore is completed and umount the share."
+
+rm -f $check_file || Error "Couldn't delete restore finished file $check_file"
+
+LogPrint "Wait until $check_file was created and there is no connection on the NFS-Port 2049."
+
+# or look at /var/lib/nfs/rmtab
+local nfs_connections=1
+while [ ! -f "$check_file" ] || [ "$nfs_connections" -gt 0 ]; do
+    local used_space
+    used_space=$(df --total --local -h --exclude-type=tmpfs --exclude-type=devtmpf | tail -n 1 | awk '{print $3}') &&
+        ProgressInfo "      Used storage space: $used_space"
+
+    sleep 5
+    nfs_connections=$(ss -tanpH state established "( sport = 2049 )" | wc -l)
+done
+
+rm -f $check_file || Error "Couldn't delete restore finished file $check_file"

usr/share/rear/restore/NFS4SERVER/default/500_stop_nfs_server.sh

@@ -0,0 +1,5 @@
+# 500_stop_nfs_server.sh
+
+rpc.nfsd 0 || :
+
+kill $(pidof rpc.mountd) || :

usr/share/rear/verify/NFS4SERVER/default/400_verify_nfs_server.sh

@@ -0,0 +1,4 @@
+# 400_verify_nfs_server.sh
+
+# Check if at least one trusted client was specified
+(( "${#NFS4SERVER_TRUSTED_CLIENTS[@]}" > 0 )) || Error "You must have defined at least one client in NFS4SERVER_TRUSTED_CLIENTS."