Implement config panel for swap management

helpers/helpers.v1.d/hardware

@@ -103,3 +103,109 @@ ynh_require_ram() {
         return 0
     fi
 }
+
+# Add swap
+#
+# usage: ynh_add_swap --size=SWAP in MiB
+# | arg: -s, --size= - Amount of SWAP to add in MiB.
+ynh_add_swap () {
+    # Declare an array to define the options of this helper.
+    declare -Ar args_array=( [s]=size= )
+    local size
+    # Manage arguments with getopts
+    ynh_handle_getopts_args "$@"
+
+    local swap_max_size=$(( $size * 1024 ))
+
+    local free_space=$(df --output=avail / | sed 1d)
+    # Because we don't want to fill the disk with a swap file, divide by 2 the available space.
+    local usable_space=$(( $free_space / 2 ))
+
+    SD_CARD_CAN_SWAP=${SD_CARD_CAN_SWAP:-0}
+
+    # Swap on SD card only if it's is specified
+    if ynh_is_main_device_a_sd_card && [ "$SD_CARD_CAN_SWAP" == "0" ]
+    then
+        ynh_print_warn --message="The main mountpoint of your system '/' is on an SD card, swap will not be added to prevent some damage to it. If you still want activate the swap, you can relaunch the command preceded by 'SD_CARD_CAN_SWAP=1'"
+        return
+    fi
+
+    # Configure swappiness
+    if [ ! -e /etc/sysctl.d/999-ynhswap.conf ]
+    then
+        echo "vm.swappiness=10" > /etc/sysctl.d/999-ynhswap.conf
+        sysctl --quiet --system
+    fi
+
+    # Compare the available space with the size of the swap.
+    # And set a acceptable size from the request
+    if [ $usable_space -ge $swap_max_size ]
+    then
+        swap_size=$swap_max_size
+    elif [ $usable_space -ge $(( $swap_max_size / 2 )) ]
+    then
+        swap_size=$(( $swap_max_size / 2 ))
+    elif [ $usable_space -ge $(( $swap_max_size / 3 )) ]
+    then
+        swap_size=$(( $swap_max_size / 3 ))
+    elif [ $usable_space -ge $(( $swap_max_size / 4 )) ]
+    then
+        swap_size=$(( $swap_max_size / 4 ))
+    else
+        echo "Not enough space left for a swap file" >&2
+        swap_size=0
+    fi
+
+    # If there's enough space for a swap, and no existing swap here
+    if [ $swap_size -ne 0 ] && [ ! -e /swap_file ]
+    then
+        # Create file
+        truncate -s 0 /swap_file
+
+        # set the No_COW attribute on the swapfile with chattr
+        # let's not fail here, as some filesystems like ext4 do not support COW
+        chattr +C /swap_file || true
+
+        # Preallocate space for the swap file, fallocate may sometime not be used, use dd instead in this case
+        if ! fallocate -l ${swap_size}K /swap_file
+        then
+            dd if=/dev/zero of=/swap_file bs=1024 count=${swap_size}
+        fi
+        chmod 0600 /swap_file
+        # Create the swap
+        mkswap /swap_file
+        # And activate it
+        swapon /swap_file
+        # Then add an entry in fstab to load this swap at each boot.
+        echo -e "/swap_file swap swap defaults 0 0 #Swap added by YunoHost config panel" >> /etc/fstab
+    fi
+}
+
+ynh_del_swap () {
+    # If there a swap at this place
+    if [ -e /swap_file ]
+    then
+        # Clean the fstab
+        sed -i "/#Swap added by YunoHost config panel/d" /etc/fstab
+        # Desactive the swap file
+        swapoff /swap_file
+        # And remove it
+        rm /swap_file
+    fi
+}
+
+# Check if the device of the main mountpoint "/" is an SD card
+#
+# [internal]
+#
+# return 0 if it's an SD card, else 1
+ynh_is_main_device_a_sd_card () {
+    local main_device=$(lsblk --output PKNAME --noheadings $(findmnt / --nofsroot --uniq --output source --noheadings --first-only))
+
+    if echo $main_device | grep --quiet "mmc" && [ $(tail -n1 /sys/block/$main_device/queue/rotational) == "0" ]
+    then
+        return 0
+    else
+        return 1
+    fi
+}

hooks/conf_regen/53-swap

@@ -0,0 +1,31 @@
+#!/bin/bash
+
+source /usr/share/yunohost/helpers
+
+do_pre_regen() {
+	:
+}
+
+do_post_regen() {
+    swapfile_enabled="$(yunohost settings get 'swap.swapfile.swapfile_enabled')"
+    swapfile_size="$(yunohost settings get 'swap.swapfile.swapfile_size')"
+
+    if [ ${swapfile_enabled} -eq 1 ]; then
+        # If a swapfile is requested
+        if [ -f /swap_file ] && [ $(stat -c%s /swap_file) -ne $swapfile_size ]; then
+            # Let's delete it first if it is not of the requested size
+            ynh_print_info --message="Deleting swap first..."
+            ynh_del_swap
+        fi
+        # create the swapfile
+        ynh_print_info --message="Attempting to create $swapfile_size MB swap..."
+        ynh_add_swap --size=$swapfile_size
+        ynh_print_info --message="A $((swap_size / 1024)) MB swap has been created."
+    else
+        # If not, make sure it is deleted
+        ynh_print_info --message="Deleting swap..."
+        ynh_del_swap
+    fi
+}
+
+do_$1_regen ${@:2}

share/config_global.toml

@@ -169,3 +169,25 @@ name = "Other"
         choices.ipv4 = "IPv4 Only"
         choices.ipv6 = "IPv6 Only"
         default = "both"
+[swap]
+name = "Swap"
+    [swap.swapfile]
+    name = "Swap file configuration"
+        [swap.swapfile.swapfile_warning]
+        ask = "Absolutely do not create a swap file if your root partition is on a SD card!"
+        help = "The intensive writing on the SD card will degrade it fast."
+        type = "alert"
+        style = "warning"
+
+        [swap.swapfile.swapfile_enabled]
+        ask = "Do you need to create a swap file?"
+        help = "A swap file will extend the available RAM by using some of your storage space."
+        type = "boolean"
+        default = false
+
+        [swap.swapfile.swapfile_size]
+        ask = "How many Mebibytes should the swap file be?"
+        help = "Only integers are accepted ( 1 MiB = 1024 B). Beware, if you reduce its current size, you may crash your server."
+        type = "number"
+        default = 1024
+        visible = "swapfile_enabled"

src/settings.py

@@ -366,3 +366,9 @@ def reconfigure_dovecot(setting_name, old_value, new_value):
             regen_conf(names=["dovecot"])
         command = ["apt-get", "-y", "remove", dovecot_package]
         subprocess.call(command, env=environment)
+
+@post_change_hook("swapfile_enabled")
+@post_change_hook("swapfile_size")
+def reconfigure_swapfile(setting_name, old_value, new_value):
+    if old_value != new_value:
+        regen_conf(names=["swap"])