From ea5adae0b2232ad09cceb00d062fa15e5f44ca2e Mon Sep 17 00:00:00 2001
From: MickLesk <47820557+MickLesk@users.noreply.github.com>
Date: Fri, 13 Nov 2026 12:30:55 +0100
Subject: [PATCH 1/2] Read the mounts once when emptying a target for a clean
 install

_cs_clean_target_dir asked mountpoint about every directory below the
target, one process each. On a node_modules tree that took minutes: 277 s
for 20,000 directories, against 1.5 s now. The mounts below the target are
read from /proc/self/mountinfo once and pruned by path, which also catches
a bind mount from the same filesystem and a mounted file. Alpine shares the
same code now; busybox mountpoint missed same-filesystem bind mounts there.
---
 lib/API.txt                         |  1 +
 lib/alpine.func                     | 45 ++++++++++++++++++++++++-----
 lib/forge.func                      | 42 ++++++++++++++++++++++-----
 tests/alpine-clean-install.sh       | 32 +++++++++-----------
 tests/forge-branch-clean-install.sh | 16 +++++-----
 tests/forge-clean-install.sh        | 42 ++++++++++++++++++++++++++-
 6 files changed, 136 insertions(+), 42 deletions(-)

diff --git a/lib/API.txt b/lib/API.txt
index 1181a97e..6a74de52 100644
--- a/lib/API.txt
+++ b/lib/API.txt
@@ -4,6 +4,7 @@ _configure_pg_cron_preload
 _cs_apt_install_optional
 _cs_clean_target_dir
 _cs_drop_pm_shim
+_cs_mounts_under
 _cs_repair_dpkg
 _cs_write_cargo_net
 _cs_write_cargo_profile
diff --git a/lib/alpine.func b/lib/alpine.func
index e37a3fdc..a08576ac 100644
--- a/lib/alpine.func
+++ b/lib/alpine.func
@@ -353,14 +353,27 @@ check_for_gh_release() {
 }
 
 # Empty a target directory before a clean install, leaving mount points and
-# CLEAN_INSTALL_KEEP paths alone. Same function as in lib/forge.func, which says
-# why it is written this way, except for how it spots a mount: busybox mountpoint
-# compares device numbers, so it misses a bind mount from the same filesystem.
+# CLEAN_INSTALL_KEEP paths alone. Same functions as in lib/forge.func, which
+# says why they are written this way.
+_cs_mounts_under() {
+  local dir="${1:?directory}" info="${3:-/proc/self/mountinfo}" mnt _
+  local -n _cs_mounts="${2:?array name}"
+  _cs_mounts=()
+  [[ -r "$info" ]] || return 1
+  while read -r _ _ _ _ mnt _; do
+    printf -v mnt '%b' "$mnt"
+    [[ "$mnt" == "$dir"/* ]] && _cs_mounts+=("$mnt")
+  done <"$info"
+  return 0
+}
+
 _cs_clean_target_dir() {
   local dir="${1:?directory}" list entry stash=""
   [[ -d "$dir" ]] || return 0
   dir="$(realpath "$dir")" # mountinfo lists resolved paths
 
+  # Moved aside rather than pruned from find: a kept path can be nested, and
+  # removing its parent would take it along. mv also keeps a symlink a symlink.
   local -a keep=()
   [[ -n "${CLEAN_INSTALL_KEEP:-}" ]] && read -ra keep <<<"$CLEAN_INSTALL_KEEP"
   if ((${#keep[@]})); then
@@ -373,14 +386,32 @@ _cs_clean_target_dir() {
     done
   fi
 
-  if ! command -v mountpoint >/dev/null 2>&1; then
+  # The mounts are read once: asking mountpoint about every directory took
+  # minutes on a node_modules tree.
+  local -a mounts=() prune=()
+  if ! _cs_mounts_under "$dir" mounts; then
+    msg_error "Cannot read /proc/self/mountinfo, so ${dir} is not emptied"
+    return 1
+  fi
+  if ((${#mounts[@]} == 0)); then
     find "${dir:?}" -mindepth 1 -maxdepth 1 -print0 | xargs -0 rm -rf --
   else
+    # -path takes a pattern, so a literal \ * ? [ in a mount path is escaped.
+    local bs='\'
+    for entry in "${mounts[@]}"; do
+      entry="${entry//"$bs"/"$bs$bs"}"
+      entry="${entry//"*"/"$bs*"}"
+      entry="${entry//"?"/"$bs?"}"
+      entry="${entry//"["/"${bs}["}"
+      prune+=(-path "$entry" -prune -o)
+    done
     list="$(mktemp)" || return 1
-    local -a skip_mounts=(\( -type d \( -exec mountpoint -q {} \; -o -exec grep -qF " {} " /proc/self/mountinfo \; \) -prune \))
-    find "${dir:?}" -mindepth 1 "${skip_mounts[@]}" -o ! -type d -print0 >"$list"
+    # Not rm -r on the list: it would hold the parents of a nested mount, and
+    # rm -r on one would empty the mount. Files first, then directories deepest
+    # first. rmdir fails on purpose on a parent that still holds a mount.
+    find "${dir:?}" -mindepth 1 "${prune[@]}" ! -type d -print0 >"$list"
     xargs -0 rm -f -- <"$list"
-    find "${dir:?}" -mindepth 1 "${skip_mounts[@]}" -o -type d -print0 >"$list"
+    find "${dir:?}" -mindepth 1 "${prune[@]}" -type d -print0 >"$list"
     sort -rz "$list" | xargs -0 rmdir -- 2>/dev/null || true
     rm -f "$list"
   fi
diff --git a/lib/forge.func b/lib/forge.func
index 5cb09959..25bb99ba 100644
--- a/lib/forge.func
+++ b/lib/forge.func
@@ -504,6 +504,21 @@ _download_source_tarball() {
   return 250
 }
 
+# Fills the array named <array> with the mount points strictly below <dir>, read
+# from mountinfo (resolved paths,  -style escapes decoded). Returns 1 when
+# mountinfo cannot be read.
+_cs_mounts_under() {
+  local dir="${1:?directory}" info="${3:-/proc/self/mountinfo}" mnt _
+  local -n _cs_mounts="${2:?array name}"
+  _cs_mounts=()
+  [[ -r "$info" ]] || return 1
+  while read -r _ _ _ _ mnt _; do
+    printf -v mnt '%b' "$mnt"
+    [[ "$mnt" == "$dir"/* ]] && _cs_mounts+=("$mnt")
+  done <"$info"
+  return 0
+}
+
 # Empty a target directory before a clean install, without touching anything
 # mounted into it. The list is written out in full before anything is removed:
 # piping find straight into `xargs rm -rf` let rm delete parents while find was
@@ -513,7 +528,7 @@ _download_source_tarball() {
 _cs_clean_target_dir() {
   local dir="${1:?directory}" list entry stash=""
   [[ -d "$dir" ]] || return 0
-  dir="${dir%/}"
+  dir="$(realpath "$dir")" # mountinfo lists resolved paths
 
   # Moved aside rather than pruned from find: a kept path can be nested, and
   # removing its parent would take it along. mv also keeps a symlink a symlink.
@@ -529,19 +544,32 @@ _cs_clean_target_dir() {
     done
   fi
 
-  # mountpoint lives in util-linux, which a minimal Alpine may not have. Without
-  # it the -exec below would fail once per directory, and there is nothing to
-  # protect anyway -- so drop the top-level entries and let rm recurse.
-  if ! command -v mountpoint >/dev/null 2>&1; then
+  # The mounts are read once: asking mountpoint about every directory took
+  # minutes on a node_modules tree.
+  local -a mounts=() prune=()
+  if ! _cs_mounts_under "$dir" mounts; then
+    msg_error "Cannot read /proc/self/mountinfo, so ${dir} is not emptied"
+    return 1
+  fi
+  if ((${#mounts[@]} == 0)); then
     find "${dir:?}" -mindepth 1 -maxdepth 1 -print0 | xargs -0 rm -rf --
   else
+    # -path takes a pattern, so a literal \ * ? [ in a mount path is escaped.
+    local bs='\'
+    for entry in "${mounts[@]}"; do
+      entry="${entry//"$bs"/"$bs$bs"}"
+      entry="${entry//"*"/"$bs*"}"
+      entry="${entry//"?"/"$bs?"}"
+      entry="${entry//"["/"${bs}["}"
+      prune+=(-path "$entry" -prune -o)
+    done
     list="$(mktemp)" || return 1
     # Not rm -r on the list: it would hold the parents of a nested mount, and
     # rm -r on one would empty the mount. Files first, then directories deepest
     # first. rmdir fails on purpose on a parent that still holds a mount.
-    find "${dir:?}" -mindepth 1 \( -type d -exec mountpoint -q {} \; -prune \) -o ! -type d -print0 >"$list"
+    find "${dir:?}" -mindepth 1 "${prune[@]}" ! -type d -print0 >"$list"
     xargs -0 rm -f -- <"$list"
-    find "${dir:?}" -mindepth 1 \( -type d -exec mountpoint -q {} \; -prune \) -o -type d -print0 >"$list"
+    find "${dir:?}" -mindepth 1 "${prune[@]}" -type d -print0 >"$list"
     sort -rz "$list" | xargs -0 rmdir -- 2>/dev/null || true
     rm -f "$list"
   fi
diff --git a/tests/alpine-clean-install.sh b/tests/alpine-clean-install.sh
index ad02e442..32f253eb 100644
--- a/tests/alpine-clean-install.sh
+++ b/tests/alpine-clean-install.sh
@@ -36,13 +36,13 @@ download_with_progress() { cp "$TEST_DIR/$archive" "$2"; }
 export HOME="$TEST_DIR/home"
 mkdir -p "$HOME" "$TEST_DIR/bin"
 
-# Any directory called mnt counts as a mount point, so no root is needed.
-cat >"$TEST_DIR/bin/mountpoint" <<'EOF'
-#!/usr/bin/env bash
-[[ "${2##*/}" == "mnt" ]]
-EOF
-chmod +x "$TEST_DIR/bin/mountpoint"
-export PATH="$TEST_DIR/bin:$PATH"
+# Every path called mnt* counts as a mount, so no root is needed: the real
+# parser reads a mountinfo written from them.
+eval "real$(declare -f _cs_mounts_under)"
+_cs_mounts_under() {
+  find "$TEST_DIR" -name 'mnt*' | sed 's/ /\\040/g; s|^|36 25 0:32 / |; s|$| rw - tmpfs tmpfs rw|' >"$TEST_DIR/mountinfo"
+  real_cs_mounts_under "$1" "$2" "$TEST_DIR/mountinfo"
+}
 
 mkdir -p "$TEST_DIR/src/app-1.0" "$TEST_DIR/flat" "$TEST_DIR/hollow/app-1.0"
 echo new >"$TEST_DIR/src/app-1.0/app"
@@ -92,19 +92,13 @@ for mode in tarball prebuild; do
   check "$mode: nested mount survives" "0 ./app ./data/mnt/file " "$(CLEAN_INSTALL=1 deploy "$mode" good.tar.gz)"
 done
 
-# busybox mountpoint misses a bind mount from the same filesystem. mountinfo has it.
-mkdir -p "$TEST_DIR/bin-bind"
-printf '#!/usr/bin/env bash\nexit 1\n' >"$TEST_DIR/bin-bind/mountpoint"
-cat >"$TEST_DIR/bin-bind/grep" <<'EOF'
-#!/usr/bin/env bash
-[[ "$2" == *"/data/bind " && "$3" == "/proc/self/mountinfo" ]]
-EOF
-chmod +x "$TEST_DIR/bin-bind/mountpoint" "$TEST_DIR/bin-bind/grep"
+# busybox mountpoint compares device numbers and missed a bind mount from the
+# same filesystem; mountinfo lists it.
 setup
-mkdir -p "$target/data/bind"
-echo mounted >"$target/data/bind/file"
-PATH="$TEST_DIR/bin-bind:$PATH" _cs_clean_target_dir "$target"
-check "bind mount from the same filesystem survives" "./data/bind/file " "$(listing)"
+mkdir -p "$target/data/mnt bind"
+echo mounted >"$target/data/mnt bind/file"
+_cs_clean_target_dir "$target"
+check "bind mount survives" "./data/mnt bind/file " "$(listing)"
 
 setup
 mv "$target" "$TEST_DIR/opt/real"
diff --git a/tests/forge-branch-clean-install.sh b/tests/forge-branch-clean-install.sh
index c0c5a89e..17b85942 100644
--- a/tests/forge-branch-clean-install.sh
+++ b/tests/forge-branch-clean-install.sh
@@ -2,7 +2,7 @@
 set -euo pipefail
 
 CORE_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)"
-eval "$(awk '/^(_cs_clean_target_dir|fetch_and_deploy_gh_branch)\(\) \{/,/^}/' "$CORE_DIR/lib/forge.func")"
+eval "$(awk '/^(_cs_mounts_under|_cs_clean_target_dir|fetch_and_deploy_gh_branch)\(\) \{/,/^}/' "$CORE_DIR/lib/forge.func")"
 
 TEST_DIR="$(mktemp -d)"
 trap 'rm -rf -- "$TEST_DIR"' EXIT
@@ -34,13 +34,13 @@ export GIT_CONFIG_VALUE_0="https://github.com/"
 export GIT_AUTHOR_NAME=test GIT_AUTHOR_EMAIL=test@example.com
 export GIT_COMMITTER_NAME=test GIT_COMMITTER_EMAIL=test@example.com
 
-# Any directory called mnt counts as a mount point, so no root is needed.
-cat >"$TEST_DIR/bin/mountpoint" <<'EOF'
-#!/usr/bin/env bash
-[[ "${2##*/}" == "mnt" ]]
-EOF
-chmod +x "$TEST_DIR/bin/mountpoint"
-export PATH="$TEST_DIR/bin:$PATH"
+# Every path called mnt* counts as a mount, so no root is needed: the real
+# parser reads a mountinfo written from them.
+eval "real$(declare -f _cs_mounts_under)"
+_cs_mounts_under() {
+  find "$TEST_DIR" -name 'mnt*' | sed 's/ /\\040/g; s|^|36 25 0:32 / |; s|$| rw - tmpfs tmpfs rw|' >"$TEST_DIR/mountinfo"
+  real_cs_mounts_under "$1" "$2" "$TEST_DIR/mountinfo"
+}
 
 git init -q -b main "$TEST_DIR/remote/owner/app"
 commit() {
diff --git a/tests/forge-clean-install.sh b/tests/forge-clean-install.sh
index 8401974c..8dcb300b 100644
--- a/tests/forge-clean-install.sh
+++ b/tests/forge-clean-install.sh
@@ -2,7 +2,7 @@
 set -euo pipefail
 
 CORE_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)"
-eval "$(awk '/^(_cs_clean_target_dir|_deploy_source_tarball|_deploy_unpacked_archive|_forge_workdir|_forge_place|_forge_disk_full)\(\) \{/,/^}/' "$CORE_DIR/lib/forge.func")"
+eval "$(awk '/^(_cs_mounts_under|_cs_clean_target_dir|_deploy_source_tarball|_deploy_unpacked_archive|_forge_workdir|_forge_place|_forge_disk_full)\(\) \{/,/^}/' "$CORE_DIR/lib/forge.func")"
 
 TEST_DIR="$(mktemp -d)"
 trap 'rm -rf -- "$TEST_DIR"' EXIT
@@ -116,6 +116,46 @@ rc=0
 FAKE_AVAIL=900000 _forge_disk_full "$TEST_DIR/dst" || rc=$?
 check "a failure with space left is not blamed on the disk" 0 "$rc"
 
+# mountinfo: only what is mounted strictly below the target, escapes decoded.
+cat >"$TEST_DIR/mountinfo" <<'EOF'
+22 1 0:20 / / rw - ext4 /dev/root rw
+30 22 0:25 / /opt/app rw - zfs tank/app rw
+31 30 0:26 / /opt/app/media\040library rw - nfs srv:/media rw
+32 30 0:27 /cfg.yml /opt/app/config.yml rw - ext4 /dev/sdb rw
+33 22 0:28 / /opt/app2 rw - tmpfs tmpfs rw
+EOF
+mounts_of() {
+  local -a found=()
+  _cs_mounts_under "$1" found "$TEST_DIR/mountinfo"
+  printf '%s|' "${found[@]}"
+}
+check "mountinfo: mounts below the target, decoded" "/opt/app/media library|/opt/app/config.yml|" "$(mounts_of /opt/app)"
+rc=0
+_cs_mounts_under /opt/app found "$TEST_DIR/no-mountinfo" || rc=$?
+check "mountinfo: unreadable is an error" 1 "$rc"
+
+# Every path called mnt* counts as a mount, so no root is needed: the real
+# parser reads a mountinfo written from them.
+eval "real$(declare -f _cs_mounts_under)"
+_cs_mounts_under() {
+  find "$TEST_DIR" -name 'mnt*' | sed 's/ /\\040/g; s|^|36 25 0:32 / |; s|$| rw - tmpfs tmpfs rw|' >"$TEST_DIR/mountinfo"
+  real_cs_mounts_under "$1" "$2" "$TEST_DIR/mountinfo"
+}
+# node_modules has tens of thousands of directories; mountpoint ran once for each.
+mkdir -p "$TEST_DIR/bin-count"
+printf '#!/usr/bin/env bash\necho x >>"%s"\nexit 1\n' "$TEST_DIR/mountpoint.calls" >"$TEST_DIR/bin-count/mountpoint"
+chmod +x "$TEST_DIR/bin-count/mountpoint"
+rm -rf "$TEST_DIR/target"
+for i in $(seq 40); do mkdir -p "$TEST_DIR/target/node_modules/p$i/lib" && echo x >"$TEST_DIR/target/node_modules/p$i/lib/index.js"; done
+mkdir -p "$TEST_DIR/target/data/mnt media" "$TEST_DIR/target/mnt[x]" "$TEST_DIR/target/a*b"
+echo mounted >"$TEST_DIR/target/data/mnt media/file"
+echo mounted >"$TEST_DIR/target/mnt[x]/file"
+echo mounted >"$TEST_DIR/target/mnt.conf"
+echo gone >"$TEST_DIR/target/a*b/file"
+PATH="$TEST_DIR/bin-count:$PATH" _cs_clean_target_dir "$TEST_DIR/target"
+check "mounts: a mounted directory and a mounted file survive, the rest goes" "./data/mnt media/file ./mnt.conf ./mnt[x]/file " "$(listing)"
+check "mounts: no process per directory" 0 "$(cat "$TEST_DIR/mountpoint.calls" 2>/dev/null | wc -l | tr -d ' ')"
+
 # The tarball mode used to return 0 whatever cp did.
 setup
 mkdir -p "$TEST_DIR/pkg/app-1.0" && echo v1 >"$TEST_DIR/pkg/app-1.0/app"

From 237c6f683d6abd4be5c011fc1b28d9280ec4fd39 Mon Sep 17 00:00:00 2001
From: MickLesk <47820557+MickLesk@users.noreply.github.com>
Date: Fri, 13 Nov 2026 15:41:16 +0100
Subject: [PATCH 2/2] Trim the comments to what a reader would get wrong

---
 lib/alpine.func                     | 11 ++---------
 lib/forge.func                      |  6 +-----
 tests/alpine-clean-install.sh       |  4 ----
 tests/forge-branch-clean-install.sh |  2 --
 tests/forge-clean-install.sh        |  4 ----
 5 files changed, 3 insertions(+), 24 deletions(-)

diff --git a/lib/alpine.func b/lib/alpine.func
index a08576ac..4ef57b0b 100644
--- a/lib/alpine.func
+++ b/lib/alpine.func
@@ -353,8 +353,7 @@ check_for_gh_release() {
 }
 
 # Empty a target directory before a clean install, leaving mount points and
-# CLEAN_INSTALL_KEEP paths alone. Same functions as in lib/forge.func, which
-# says why they are written this way.
+# CLEAN_INSTALL_KEEP paths alone, as in lib/forge.func.
 _cs_mounts_under() {
   local dir="${1:?directory}" info="${3:-/proc/self/mountinfo}" mnt _
   local -n _cs_mounts="${2:?array name}"
@@ -372,8 +371,6 @@ _cs_clean_target_dir() {
   [[ -d "$dir" ]] || return 0
   dir="$(realpath "$dir")" # mountinfo lists resolved paths
 
-  # Moved aside rather than pruned from find: a kept path can be nested, and
-  # removing its parent would take it along. mv also keeps a symlink a symlink.
   local -a keep=()
   [[ -n "${CLEAN_INSTALL_KEEP:-}" ]] && read -ra keep <<<"$CLEAN_INSTALL_KEEP"
   if ((${#keep[@]})); then
@@ -386,8 +383,6 @@ _cs_clean_target_dir() {
     done
   fi
 
-  # The mounts are read once: asking mountpoint about every directory took
-  # minutes on a node_modules tree.
   local -a mounts=() prune=()
   if ! _cs_mounts_under "$dir" mounts; then
     msg_error "Cannot read /proc/self/mountinfo, so ${dir} is not emptied"
@@ -406,9 +401,7 @@ _cs_clean_target_dir() {
       prune+=(-path "$entry" -prune -o)
     done
     list="$(mktemp)" || return 1
-    # Not rm -r on the list: it would hold the parents of a nested mount, and
-    # rm -r on one would empty the mount. Files first, then directories deepest
-    # first. rmdir fails on purpose on a parent that still holds a mount.
+    # Files first, then directories deepest first; rmdir fails on purpose on a parent that holds a mount.
     find "${dir:?}" -mindepth 1 "${prune[@]}" ! -type d -print0 >"$list"
     xargs -0 rm -f -- <"$list"
     find "${dir:?}" -mindepth 1 "${prune[@]}" -type d -print0 >"$list"
diff --git a/lib/forge.func b/lib/forge.func
index 25bb99ba..c7718798 100644
--- a/lib/forge.func
+++ b/lib/forge.func
@@ -504,9 +504,7 @@ _download_source_tarball() {
   return 250
 }
 
-# Fills the array named <array> with the mount points strictly below <dir>, read
-# from mountinfo (resolved paths,  -style escapes decoded). Returns 1 when
-# mountinfo cannot be read.
+# Fills the array named <array> with the mount points strictly below <dir>; returns 1 when mountinfo is unreadable.
 _cs_mounts_under() {
   local dir="${1:?directory}" info="${3:-/proc/self/mountinfo}" mnt _
   local -n _cs_mounts="${2:?array name}"
@@ -544,8 +542,6 @@ _cs_clean_target_dir() {
     done
   fi
 
-  # The mounts are read once: asking mountpoint about every directory took
-  # minutes on a node_modules tree.
   local -a mounts=() prune=()
   if ! _cs_mounts_under "$dir" mounts; then
     msg_error "Cannot read /proc/self/mountinfo, so ${dir} is not emptied"
diff --git a/tests/alpine-clean-install.sh b/tests/alpine-clean-install.sh
index 32f253eb..2fce3d24 100644
--- a/tests/alpine-clean-install.sh
+++ b/tests/alpine-clean-install.sh
@@ -36,8 +36,6 @@ download_with_progress() { cp "$TEST_DIR/$archive" "$2"; }
 export HOME="$TEST_DIR/home"
 mkdir -p "$HOME" "$TEST_DIR/bin"
 
-# Every path called mnt* counts as a mount, so no root is needed: the real
-# parser reads a mountinfo written from them.
 eval "real$(declare -f _cs_mounts_under)"
 _cs_mounts_under() {
   find "$TEST_DIR" -name 'mnt*' | sed 's/ /\\040/g; s|^|36 25 0:32 / |; s|$| rw - tmpfs tmpfs rw|' >"$TEST_DIR/mountinfo"
@@ -92,8 +90,6 @@ for mode in tarball prebuild; do
   check "$mode: nested mount survives" "0 ./app ./data/mnt/file " "$(CLEAN_INSTALL=1 deploy "$mode" good.tar.gz)"
 done
 
-# busybox mountpoint compares device numbers and missed a bind mount from the
-# same filesystem; mountinfo lists it.
 setup
 mkdir -p "$target/data/mnt bind"
 echo mounted >"$target/data/mnt bind/file"
diff --git a/tests/forge-branch-clean-install.sh b/tests/forge-branch-clean-install.sh
index 17b85942..fe4d8c76 100644
--- a/tests/forge-branch-clean-install.sh
+++ b/tests/forge-branch-clean-install.sh
@@ -34,8 +34,6 @@ export GIT_CONFIG_VALUE_0="https://github.com/"
 export GIT_AUTHOR_NAME=test GIT_AUTHOR_EMAIL=test@example.com
 export GIT_COMMITTER_NAME=test GIT_COMMITTER_EMAIL=test@example.com
 
-# Every path called mnt* counts as a mount, so no root is needed: the real
-# parser reads a mountinfo written from them.
 eval "real$(declare -f _cs_mounts_under)"
 _cs_mounts_under() {
   find "$TEST_DIR" -name 'mnt*' | sed 's/ /\\040/g; s|^|36 25 0:32 / |; s|$| rw - tmpfs tmpfs rw|' >"$TEST_DIR/mountinfo"
diff --git a/tests/forge-clean-install.sh b/tests/forge-clean-install.sh
index 8dcb300b..7e4e4fae 100644
--- a/tests/forge-clean-install.sh
+++ b/tests/forge-clean-install.sh
@@ -116,7 +116,6 @@ rc=0
 FAKE_AVAIL=900000 _forge_disk_full "$TEST_DIR/dst" || rc=$?
 check "a failure with space left is not blamed on the disk" 0 "$rc"
 
-# mountinfo: only what is mounted strictly below the target, escapes decoded.
 cat >"$TEST_DIR/mountinfo" <<'EOF'
 22 1 0:20 / / rw - ext4 /dev/root rw
 30 22 0:25 / /opt/app rw - zfs tank/app rw
@@ -134,14 +133,11 @@ rc=0
 _cs_mounts_under /opt/app found "$TEST_DIR/no-mountinfo" || rc=$?
 check "mountinfo: unreadable is an error" 1 "$rc"
 
-# Every path called mnt* counts as a mount, so no root is needed: the real
-# parser reads a mountinfo written from them.
 eval "real$(declare -f _cs_mounts_under)"
 _cs_mounts_under() {
   find "$TEST_DIR" -name 'mnt*' | sed 's/ /\\040/g; s|^|36 25 0:32 / |; s|$| rw - tmpfs tmpfs rw|' >"$TEST_DIR/mountinfo"
   real_cs_mounts_under "$1" "$2" "$TEST_DIR/mountinfo"
 }
-# node_modules has tens of thousands of directories; mountpoint ran once for each.
 mkdir -p "$TEST_DIR/bin-count"
 printf '#!/usr/bin/env bash\necho x >>"%s"\nexit 1\n' "$TEST_DIR/mountpoint.calls" >"$TEST_DIR/bin-count/mountpoint"
 chmod +x "$TEST_DIR/bin-count/mountpoint"