From 6050da7dbb2c2e8f1dd612888318810e7624af84 Mon Sep 17 00:00:00 2001
From: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Date: Fri, 2 Oct 2026 18:42:36 +0200
Subject: [PATCH] Revert "deb: run the rootless build step under fakeroot,
 sharing the state"
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This reverts commit 5f36a54db42e0e5b8f5243dded89f68cd93fa689.

Fakeroot's IPC degrades under kernel-scale parallel builds: a
linux-riscv build with make -j plus LTO floods the faked daemon and
libfakeroot prints 'internal error: payload not recognized' per
mangled message, with the ownership database losing entries. The
benefit the wrap bought is vacuous anyway: the .deb is assembled in
the binary step's own fakeroot session, which records files unknown
to its database as root-owned — verified with a sysroot package
whose build chown fails: the produced .deb still carries root/root.

A rules chown failing for the unprivileged build user stays expected
and harmless; the visible noise is collapsed at the classifier level
instead (next commit). The bare build step also matches modern dpkg
semantics: with Rules-Requires-Root: binary-targets (pkh's default
export), dpkg-buildpackage itself runs the build targets unprivileged
and fakes root only for the binary targets.
---
 src/deb/local.rs | 57 ++++++++++--------------------------------------
 1 file changed, 12 insertions(+), 45 deletions(-)

diff --git a/src/deb/local.rs b/src/deb/local.rs
index 3a7441d..5c5d055 100644
--- a/src/deb/local.rs
+++ b/src/deb/local.rs
@@ -250,14 +250,6 @@ fn rules_command<'a>(
     }
 }
 
-/// The fakeroot state file shared by the rules steps of a rootless
-/// build, in the upload directory next to the staged tree: outside the
-/// package tree, so it pollutes neither the sources nor the collected
-/// artifacts.
-fn fakeroot_state_file(upload_dir: &str) -> PathBuf {
-    Path::new(upload_dir).join(".pkh-fakeroot.state")
-}
-
 #[allow(clippy::too_many_arguments)]
 pub async fn build(
     package: &str,
@@ -688,10 +680,16 @@ pub async fn build(
         .unwrap_or_else(|| "binary-targets".to_string());
     env.insert("DEB_RULES_REQUIRES_ROOT".to_string(), rules_requires_root);
 
-    // Rootless builds: the rules (fakeroot-wrapped, see below) run as an
-    // unprivileged user owning the staged tree. Everything before this
-    // point - dependency installation, quilt patch application, staging
-    // cleanup - legitimately needs the context's root and stays with it.
+    // Rootless builds: the rules run as an unprivileged user owning the
+    // staged tree. Everything before this point - dependency installation,
+    // quilt patch application, staging cleanup - legitimately needs the
+    // context's root and stays with it. The build step runs BARE (no
+    // fakeroot): fakeroot's IPC degrades under kernel-scale parallel
+    // builds ('libfakeroot internal error: payload not recognized' per
+    // LTO/make -j process flood), and a rules chown that fails for the
+    // build user is cosmetic — the .deb is assembled in the binary step's
+    // own fakeroot session, where files unknown to its database are
+    // recorded as root-owned anyway.
     let rule_ids = match build_user {
         Some(_) => {
             let workroot = Path::new(package_dir_str)
@@ -704,34 +702,12 @@ pub async fn build(
         None => None,
     };
 
-    // Rootless: the rules run under fakeroot with one session state
-    // shared between the build and binary steps, the way
-    // dpkg-buildpackage -rfakeroot wraps every rules target. An
-    // ownership change made during the build (a sysroot chown) then
-    // succeeds — faked — and carries into the .deb, instead of failing
-    // per file with EPERM spam. With the context's own user the build
-    // step runs bare; the binary step keeps its unconditional wrap.
-    let fakeroot_state = fakeroot_state_file(upload_dir);
-    if rule_ids.is_some() {
-        // A state left by an interrupted previous attempt must not
-        // seed this session.
-        let _ = ctx.command("rm").arg("-f").arg(&fakeroot_state).status();
-    }
-    let mut rules = match rule_ids.as_ref() {
-        Some(_) => {
-            let mut cmd = rules_command(&ctx, rule_ids.as_ref(), "fakeroot");
-            cmd.arg("-s").arg(&fakeroot_state).arg("debian/rules");
-            cmd
-        }
-        None => rules_command(&ctx, None, "debian/rules"),
-    };
-
     // Run the build step
     log::debug!("Building (debian/rules build) package...");
     enter_phase(view, Phase::Building, profiler);
     let started = Instant::now();
     let status = cap(
-        rules
+        rules_command(&ctx, rule_ids.as_ref(), "debian/rules")
             .current_dir(package_dir_str)
             .envs(env.clone())
             .arg("build"),
@@ -760,17 +736,8 @@ pub async fn build(
     // Run the 'binary' step to produce deb
     enter_phase(view, Phase::ProducingBinaries, profiler);
     let started = Instant::now();
-    let mut rules = rules_command(&ctx, rule_ids.as_ref(), "fakeroot");
-    if rule_ids.is_some() {
-        // Pick up the ownership changes the build step recorded.
-        rules
-            .arg("-i")
-            .arg(&fakeroot_state)
-            .arg("-s")
-            .arg(&fakeroot_state);
-    }
     let status = cap(
-        rules
+        rules_command(&ctx, rule_ids.as_ref(), "fakeroot")
             .current_dir(package_dir_str)
             .envs(env.clone())
             .arg("debian/rules")