package: Add Debian postinst script (#13)

Cargo.toml

@@ -129,6 +129,8 @@ assets = [
     [ "LICENSE", "usr/share/doc/qcp/", "644" ],
     # gzip -9n < CHANGELOG.md > misc/changelog.gz
     [ "misc/changelog.gz", "usr/share/doc/qcp/", "644" ],
-    [ "misc/20-qcp.conf", "etc/sysctl.d/", "644" ],
+    [ "misc/20-qcp.conf", "etc/sysctl.d/", "644" ], # this is automatically recognised as a conffile
     [ "misc/qcp.1", "usr/share/man/man1/", "644" ],
 ]
+maintainer-scripts="debian"
+depends = "$auto,debconf"

debian/config

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+set -e
+
+if [ -e /usr/share/debconf/confmodule ]; then
+    . /usr/share/debconf/confmodule
+    db_version 2.0
+    db_capb
+    db_settitle qcp/title
+fi
+
+# We cannot meaningfully preconfigure as postinst checks the filesystem at runtime.

debian/postinst

@@ -0,0 +1,74 @@
+#!/bin/sh
+
+set -e
+
+# By Debian policy, packages must not ask unnecessary questions.
+#
+# Therefore, we examine the persistent sysctl directories to see
+# if there are any mentions of the sysctls we want to set.
+# If not, we presume that the system has no special requirements
+# (this is expected to be the general case).
+
+SYSCTL_FILE=20-qcp.conf
+SYSCTL_PATH=/etc/sysctl.d/${SYSCTL_FILE}
+
+. /usr/share/debconf/confmodule
+db_version 2.0
+db_capb
+db_settitle qcp/title
+
+#when testing this script, this line resets the db:
+#db_fset qcp/sysctl_clash seen false
+
+check_for_clashing_sysctls() {
+    for DIR in /etc/sysctl.d /usr/lib/sysctl.d; do
+        if grep -qcr -e net.core.rmem_max -e net.core.wmem_max --exclude "*${SYSCTL_FILE}*" ${DIR}; then
+            return 0
+        fi
+    done
+    return 1
+}
+
+activate_our_sysctls() {
+    sysctl -w -p ${SYSCTL_PATH}
+}
+
+disable_our_file() {
+    if [ -e ${SYSCTL_PATH} ]; then
+        mv -f ${SYSCTL_PATH} ${SYSCTL_PATH}.disabled
+    fi
+}
+
+try_to_enable_our_file() {
+    if [ -e ${SYSCTL_PATH}.disabled ]; then
+        mv -f ${SYSCTL_PATH}.disabled ${SYSCTL_PATH}
+    fi
+}
+
+alert_sysadmin() {
+    db_input high qcp/sysctl_clash || true
+    db_go || true
+
+    db_get qcp/sysctl_clash || true
+    case "$RET" in
+        "install and activate now")
+            try_to_enable_our_file
+            activate_our_sysctls
+        ;;
+        "install but do NOT activate")
+            try_to_enable_our_file
+            # do nothing
+        ;;
+        "do not install")
+            # they don't want it, OK
+            disable_our_file
+        ;;
+    esac
+}
+
+if check_for_clashing_sysctls; then
+    alert_sysadmin
+else
+    # No clashes; proceed quietly.
+    activate_our_sysctls
+fi

debian/postrm

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+set -e
+
+if [ -e /usr/share/debconf/confmodule ]; then
+. /usr/share/debconf/confmodule
+db_version 2
+
+case "$1" in
+purge)
+    # Remove my changes to the db.
+    if [ -e /usr/share/debconf/confmodule ]; then
+        . /usr/share/debconf/confmodule
+        db_version 2
+        db_purge
+    fi
+    ;;
+esac
+
+fi

debian/templates

@@ -0,0 +1,16 @@
+Template: qcp/title
+Type: title
+Description: qcp sysctl files
+
+Template: qcp/sysctl_clash
+Type: select
+Choices: install and activate now, install but do NOT activate, do not install
+Default: install and activate now
+Description: Install sysctl files for qcp?
+ qcp has detected a possible sysctl clash!
+ .
+ qcp would like to install sysctl files to configure the kernel for good performance.
+ .
+ The sysctls used by qcp are:    net.core.rmem_max  net.core.wmem_max
+ .
+ sysctl config files may be found in:  /etc/sysctl.d  /usr/lib/sysctl.d