From f27fa0d05bc7744234693a41f7cd04f76f35c0ed Mon Sep 17 00:00:00 2001
From: CyberLeo <cyberleo@cyberleo.net>
Date: Mon, 11 Jun 2012 09:01:02 -0500
Subject: [PATCH] j: add fstab maintenance hooks

Hooks to mount and umount mountpoints within chroot based on the
contents of an fstab file; and maintain an mtab file.
---
 j      | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 mount  |  1 +
 umount |  1 +
 3 files changed, 84 insertions(+), 7 deletions(-)
 create mode 120000 mount
 create mode 120000 umount

diff --git a/j b/j
index e69559d..9014e18 100755
--- a/j
+++ b/j
@@ -31,6 +31,10 @@ Usage:
 
   eval    evaluate a shell command line within the chroot
 
+  mount   mount chroot filesystems according to chroot fstab
+
+  umount  umount chroot filesystems that were mounted with 'mount'
+
 EOF
   exit 1
 }
@@ -136,6 +140,9 @@ j_params() {
       return 1
     fi
 
+    # Does this have a valid fstab file?
+    [ -f "${jdir}/fstab" ] && jfstab="${jdir}/fstab"
+
     # Where is the shell?
     jshell=""
     for shell in /bin/bash /usr/bin/bash /usr/local/bin/bash /bin/sh
@@ -152,7 +159,7 @@ j_params() {
       return 1
     fi
 
-    printf "jerror='' jname='%s' jdir='%s' jroot='%s' jshell='%s'\n" "${jname}" "${jdir}" "${jroot}" "${jshell}"
+    printf "jerror='' jname='%s' jdir='%s' jroot='%s' jfstab='%s' jshell='%s'\n" "${jname}" "${jdir}" "${jroot}" "${jfstab}" "${jshell}"
   )
 }
 
@@ -284,14 +291,64 @@ j_status() {
   done
 }
 
-# Mount /dev/pts and /proc in the chroot
+# Copy a mount from the host (for things like /dev, /proc, /sys, et alia)
+j_fstab_copy_mount() {
+  grep -Eq "${1}[[:space:]]" "${tmp_fstab}" || grep -E \
+    "[[:space:]]${1}[[:space:]]" /proc/mounts | head -n 1 >> "${tmp_fstab}"
+}
+
+# Prepare fstab for use:
+# * Strip comments
+# * Make sure certain required mounts exist (/dev/pts, /proc)
+# * Sort by mountpoint, to ensure mounts are performed in the correct order
+j_fstab_synthesize() {
+  local tmp_fstab="$(mktemp "${jdir}/.fstab.XXXXXXXX")"
+  [ -f "${jfstab}" ] && sed -e 's/#.*$//; /^\W*$/d' "${jfstab}" > "${tmp_fstab}"
+  j_fstab_copy_mount "/dev/pts"
+  j_fstab_copy_mount "/proc"
+  sort -k2 "${tmp_fstab}"
+  rm -f "${tmp_fstab}"
+}
+
+# Process fstab file and mount the filesystems therein; if no fstab file (or if
+# excludes certain critical filesystems) then augment it. This will also maintain
+# an mtab file so they can be unmounted later (and so df works inside chroot).
+#
+# All mountpoints listed in this file will be prepended with ${jroot} prior to
+# their being mounted or umounted! Make sure the fstab mountpoints are relative
+# to the chroot root!
+j_fstab_mount() {
+  echo "rootfs / rootfs rw 0 0" > "${jdir}/mtab"
+  j_fstab_synthesize | while read src dir type opts fsck dump
+  do
+    mkdir -p "${dir}" || break
+    mount -t "${type}" -o "${opts}" "${src}" "${jroot}/${dir}" || break
+    printf "%s %s %s %s 0 0\n" "${src}" "/${dir##/}" "${type}" "${opts}" >> "${jdir}/mtab"
+  done
+}
+
+# Process fstab and mtab files and unmount the filesystems therein (opposite j_fstab_mount)
+j_fstab_umount() {
+  [ -s "${jdir}/mtab" ] || j_fstab_synthesize > "${jdir}/mtab"
+  tac "${jdir}/mtab" | while read src dir unused
+  do
+    # Mounted?
+    grep -Eq "[[:space:]]${jroot}${dir%%/}[[:space:]]" /proc/mounts || continue
+    umount -f "${jroot}/${dir}" || umount -l "${jroot}/${dir}" || break
+  done
+  :>"${jdir}/mtab"
+}
+
+# Start up chroot
 j_start() {
   jname="${1:-${jname}}"
   j_up "${jname}" && return 0
   eval "$(j_params "${jname}")"
   meh "starting ${jname} ..."
-  mount -t devpts devpts "${jroot}/dev/pts"
-  mount -t proc proc "${jroot}/proc"
+
+  # Mount filesystems and copy in /etc/mtab
+  j_fstab_mount
+  cp "${jdir}/mtab" "${jroot}/etc/mtab"
 
   # Copy in ipcc and launch ipcd
   j_ipc_setup
@@ -319,13 +376,14 @@ j_eval() {
   env -i ${jenv} /usr/bin/chroot "${jroot}" /bin/su "${juser:-${USER}}" -c "${*}"
 }
 
+# Invoke a shell within the chroot
 j_shell() {
   jname="${1:-${jname}}"
   eval "$(j_params "${jname}")"
   j_eval "${jname}" "cd; exec ${jshell} -l"
 }
 
-# Unmount /dev/pts and /proc in the chroot
+# Shut down chroot
 j_stop() {
   jname="${1:-${jname}}"
   eval "$(j_params "${jname}")"
@@ -338,8 +396,8 @@ j_stop() {
   # Terminate ipcd
   j_ipc_stop
 
-  umount "${jroot}/proc"
-  umount "${jroot}/dev/pts"
+  # Unmount filesystems
+  j_fstab_umount
 }
 
 # Send a signal to all processes inside a chroot, if possible
@@ -358,6 +416,7 @@ j_signal() {
   fi
 }
 
+# Kill all processes inside chroot (TERM, then KILL)
 j_kill() {
   jname="${1:-${jname}}"
   eval "$(j_params "${jname}")"
@@ -368,6 +427,20 @@ j_kill() {
   j_signal "KILL" "${jname}"
 }
 
+# Hook to allow mounting chroot mounts from command line
+j_mount() {
+  jname="${1:-${jname}}"
+  eval "$(j_params "${jname}")"
+  j_fstab_mount
+}
+
+# Hook to allow unmounting chroot mounts from command line
+j_umount() {
+  jname="${1:-${jname}}"
+  eval "$(j_params "${jname}")"
+  j_fstab_umount
+}
+
 case "${cmd}" in
 init|create) j_init "${jname}" "${@}" ;;
 ls|list) j_ls ;;
@@ -377,5 +450,7 @@ shell|enter) j_shell "${jname}" ;;
 eval) j_eval "${jname}" "${*}" ;;
 stop) j_stop "${jname}" ;;
 kill) j_kill "${jname}" ;;
+mount) j_mount "${jname}" ;;
+umount) j_umount "${jname}" ;;
 *) pebkac ;;
 esac
diff --git a/mount b/mount
new file mode 120000
index 0000000..0fe2fa5
--- /dev/null
+++ b/mount
@@ -0,0 +1 @@
+j
\ No newline at end of file
diff --git a/umount b/umount
new file mode 120000
index 0000000..0fe2fa5
--- /dev/null
+++ b/umount
@@ -0,0 +1 @@
+j
\ No newline at end of file
-- 
2.42.0