feat: support bind mounting a tmpfs

A .cache can be bind mounted into the container to save the caches for
reuse, but sometimes we want to exclude specific caches (because they
don't work well, e.g. bazel's).

Component: makechrootpkg

4 files changed, 34 insertions, 20 deletions

diff --git a/contrib/completion/bash/devtools.in b/contrib/completion/bash/devtools.in
index 4073efe..9025b46 100644
--- a/contrib/completion/bash/devtools.in
+++ b/contrib/completion/bash/devtools.in
@@ -27,6 +27,7 @@ _makechrootpkg_args=(
 	-I
 	-l
 	-n
+	-t
 	-T
 	-U
 	-x
@@ -36,6 +37,7 @@ _makechrootpkg_args_D_opts() { _filedir -d; }
 _makechrootpkg_args_r_opts() { _filedir -d; }
 _makechrootpkg_args_I_opts() { _filedir '*.pkg.tar.*'; }
 _makechrootpkg_args_l_opts() { _filedir -d; }
+_makechrootpkg_args_t_opts() { _filedir -d; }
 _makechrootpkg_args_U_opts() { :; }
 _makechrootpkg_args_x_opts() { _devtools_completions_inspect; }
 _makechrootpkg() { __devtools_complete _makechrootpkg; }
diff --git a/contrib/completion/zsh/_devtools.in b/contrib/completion/zsh/_devtools.in
index d38733f..5c1b264 100644
--- a/contrib/completion/zsh/_devtools.in
+++ b/contrib/completion/zsh/_devtools.in
@@ -222,6 +222,7 @@ _makechrootpkg_args=(
 	'-c[Clean the chroot before building]'
 	'*-d[Bind directory into build chroot as read-write]:bind_dir_rw:_files -/'
 	'*-D[Bind directory into build chroot as read-only]:bind_dir_ro:_files -/'
+	'*-t[Mount a tmpfs at directory]:tmpfs_dir:_files -/'
 	'-u[Update the working copy of the chroot before building]'
 	'-r[The chroot dir to use]:chroot_dir:_files -/'
 	'*-I[Install a package into the working copy]:target:_files -g "*.pkg.tar.*(.)"'
diff --git a/doc/man/makechrootpkg.1.asciidoc b/doc/man/makechrootpkg.1.asciidoc
index 3aa1be5..34ba199 100644
--- a/doc/man/makechrootpkg.1.asciidoc
+++ b/doc/man/makechrootpkg.1.asciidoc
@@ -45,6 +45,9 @@ Options
 *-D* <dir>::
 	Bind directory into build chroot as read-only
 
+*-t* <dir>[:opts]::
+	Mount a tmpfs at 'dir'. See the '--tmpfs' argument in systemd-nspawn(1) for more details.
+
 *-u*::
 	Update the working copy of the chroot before building
 	This is useful for rebuilds without dirtying the pristine
@@ -76,5 +79,9 @@ Options
 *-x* <when>::
 	Inspect chroot after build, possible modes are 'never' (default), 'always' or 'failure'
 
+See Also
+--------
+
+systemd-nspawn(1)
 
 include::include/footer.asciidoc[]
diff --git a/src/makechrootpkg.in b/src/makechrootpkg.in
index 459f7ce..9df14e8 100644
--- a/src/makechrootpkg.in
+++ b/src/makechrootpkg.in
@@ -38,6 +38,7 @@ inspect=never
 
 bindmounts_ro=()
 bindmounts_rw=()
+bindmounts_tmpfs=()
 
 copy=$USER
 [[ -n ${SUDO_USER:-} ]] && copy=$SUDO_USER
@@ -65,23 +66,24 @@ usage() {
 	echo "Default makepkg args: ${default_makepkg_args[*]}"
 	echo ''
 	echo 'Flags:'
-	echo '-h         This help'
-	echo '-c         Clean the chroot before building'
-	echo '-d <dir>   Bind directory into build chroot as read-write'
-	echo '-D <dir>   Bind directory into build chroot as read-only'
-	echo '-u         Update the working copy of the chroot before building'
-	echo '           This is useful for rebuilds without dirtying the pristine'
-	echo '           chroot'
-	echo '-r <dir>   The chroot dir to use'
-	echo '-I <pkg>   Install a package into the working copy of the chroot'
-	echo '-l <copy>  The directory to use as the working copy of the chroot'
-	echo '           Useful for maintaining multiple copies'
-	echo "           Default: $copy"
-	echo '-n         Run namcap on the package'
-	echo '-C         Run checkpkg on the package'
-	echo '-T         Build in a temporary directory'
-	echo '-U         Run makepkg as a specified user'
-	echo '-x <when>  Inspect chroot after build (never, always, failure)'
+	echo '-h                This help'
+	echo '-c                Clean the chroot before building'
+	echo '-d <dir>          Bind directory into build chroot as read-write'
+	echo '-D <dir>          Bind directory into build chroot as read-only'
+	echo '-t <dir[:opts]>   Mount a tmpfs at directory'
+	echo '-u                Update the working copy of the chroot before building'
+	echo '                  This is useful for rebuilds without dirtying the pristine'
+	echo '                  chroot'
+	echo '-r <dir>          The chroot dir to use'
+	echo '-I <pkg>          Install a package into the working copy of the chroot'
+	echo '-l <copy>         The directory to use as the working copy of the chroot'
+	echo '                  Useful for maintaining multiple copies'
+	echo "                  Default: $copy"
+	echo '-n                Run namcap on the package'
+	echo '-C                Run checkpkg on the package'
+	echo '-T                Build in a temporary directory'
+	echo '-U                Run makepkg as a specified user'
+	echo '-x <when>         Inspect chroot after build (never, always, failure)'
 	exit 1
 }
 
@@ -148,7 +150,7 @@ install_packages() {
 	pkgnames=("${install_pkgs[@]##*/}")
 
 	cp -- "${install_pkgs[@]}" "$copydir/root/"
-	arch-nspawn "$copydir" "${bindmounts_ro[@]}" "${bindmounts_rw[@]}" \
+	arch-nspawn "$copydir" "${bindmounts_ro[@]}" "${bindmounts_rw[@]}" "${bindmounts_tmpfs[@]}" \
 		pacman -U --noconfirm --ask=4 -- "${pkgnames[@]/#//root/}"
 	ret=$?
 	rm -- "${pkgnames[@]/#/$copydir/root/}"
@@ -291,11 +293,12 @@ move_products() {
 }
 # }}}
 
-while getopts 'hcur:I:l:nCTD:d:U:x:' arg; do
+while getopts 'hcur:I:l:nCTD:d:U:x:t:' arg; do
 	case "$arg" in
 		c) clean_first=1 ;;
 		D) bindmounts_ro+=("--bind-ro=$OPTARG") ;;
 		d) bindmounts_rw+=("--bind=$OPTARG") ;;
+		t) bindmounts_tmpfs+=("--tmpfs=$OPTARG") ;;
 		u) update_first=1 ;;
 		r) passeddir="$OPTARG" ;;
 		I) install_pkgs+=("$OPTARG") ;;
@@ -365,7 +368,7 @@ if [[ ! -d $copydir ]] || (( clean_first )); then
 fi
 
 (( update_first )) && arch-nspawn "$copydir" \
-		"${bindmounts_ro[@]}" "${bindmounts_rw[@]}" \
+		"${bindmounts_ro[@]}" "${bindmounts_rw[@]}" "${bindmounts_tmpfs[@]}" \
 		pacman -Syuu --noconfirm
 
 if [[ -n ${install_pkgs[*]:-} ]]; then
@@ -390,6 +393,7 @@ nspawn_build_args=(
 	--tmpfs="/tmp:${tmp_opts}"
 	"${bindmounts_ro[@]}"
 	"${bindmounts_rw[@]}"
+	"${bindmounts_tmpfs[@]}"
 )
 
 if arch-nspawn "$copydir" \