composefs,centos-9: Enable rhel9 cargo feature for kernel 5.14 loopback fallback

CentOS Stream 9 ships kernel 5.14, which cannot mount an erofs image
directly from a file descriptor. composefs-rs provides a `rhel9` feature
in composefs-ctl (and forwarded through bootc-initramfs-setup) that works
around this by loopifying the image file into a /dev/loopN block device
before mounting it.

Without this feature enabled at build time, bootc install on centos-9 with
the composefs backend fails with ENOTBLK ('Block device required', errno 15)
when the initramfs setup code tries to mount the composefs/erofs image.

Wire up the feature in two places:
- Makefile: extend CARGO_FEATURES_DEFAULT to also emit `rhel9` when
  building on a RHEL-like OS with VERSION_ID=9.
- bootc.spec: add a `rhel9` bcond gated on `%{?rhel} == 9` and pass
  it to all three cargo build invocations and to %make_install.

With the build fix in place, remove the ci.yml exclude that was
suppressing centos-9 + composefs testing in test-integration.

Closes: #1812

Assisted-by: AI
Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

.github/workflows/ci.yml

@@ -236,9 +236,6 @@ jobs:
         seal_state: ["sealed", "unsealed"]
 
         exclude:
-          # https://github.com/bootc-dev/bootc/issues/1812
-          - test_os: centos-9
-            variant: composefs
           - seal_state: "sealed"
             boot_type: bls
           - seal_state: "sealed"

Makefile

@@ -29,7 +29,15 @@ prefix ?= /usr
 # We may in the future also want to include Fedora+derivatives as
 # the code is really tiny.
 # (Note we should also make installation of the units conditional on the rhsm feature)
-CARGO_FEATURES_DEFAULT ?= $(shell . /usr/lib/os-release; if echo "$$ID_LIKE" |grep -qF rhel; then echo rhsm; fi)
+#
+# Enable the rhel9 feature on RHEL/CentOS Stream 9, which runs kernel 5.14.
+# That kernel cannot mount an erofs image directly from a file descriptor;
+# composefs-ctl's rhel9 feature activates a loopback-device fallback instead.
+CARGO_FEATURES_DEFAULT ?= $(shell . /usr/lib/os-release; \
+  features=""; \
+  if echo "$$ID_LIKE" | grep -qF rhel; then features="$$features rhsm"; fi; \
+  if echo "$$ID_LIKE" | grep -qF rhel && [ "$$VERSION_ID" = "9" ]; then features="$$features rhel9"; fi; \
+  echo $$features)
 # You can set this to override all cargo features, including the defaults
 CARGO_FEATURES ?= $(CARGO_FEATURES_DEFAULT)
 

contrib/packaging/bootc.spec

@@ -12,6 +12,14 @@
     %bcond_with rhsm
 %endif
 
+# kernel 5.14 (RHEL/CentOS 9) cannot mount an erofs image directly from a file
+# descriptor; composefs-ctl's rhel9 feature enables a loopback-device fallback.
+%if 0%{?rhel} == 9
+    %bcond_without rhel9
+%else
+    %bcond_with rhel9
+%endif
+
 %global rust_minor %(rustc --version | cut -f2 -d" " | cut -f2 -d".")
 
 # https://github.com/bootc-dev/bootc/issues/1640
@@ -132,13 +140,16 @@ make manpages
 # Build all binaries
 %if 0%{?container_build}
 # Container build: use cargo directly with cached dependencies to avoid RPM macro overhead
-cargo build -j%{_smp_build_ncpus} --release %{?with_rhsm:--features rhsm} --bins
+cargo build -j%{_smp_build_ncpus} --release %{?with_rhsm:--features rhsm} %{?with_rhel9:--features rhel9} --bins
 %else
 # Non-container build: use RPM macros for proper dependency tracking
 %if %new_cargo_macros
-    %cargo_build %{?with_rhsm:-f rhsm} -- --bins
+    # Note: %%cargo_build's own -f option only accepts a single value, so a
+    # second -f would silently clobber the first; pass extra features as
+    # plain --features args after -- instead, which cargo unions correctly.
+    %cargo_build -- %{?with_rhsm:--features rhsm} %{?with_rhel9:--features rhel9} --bins
 %else
-    %cargo_build %{?with_rhsm:--features rhsm} -- --bins
+    %cargo_build %{?with_rhsm:--features rhsm} %{?with_rhel9:--features rhel9} -- --bins
 %endif
 %endif
 
@@ -152,7 +163,7 @@ sed -i -e '/https:\/\//d' cargo-vendor.txt
 
 %install
 # Pass CARGO_FEATURES explicitly to prevent auto-detection rebuild in install environment
-%make_install INSTALL="install -p -c" CARGO_FEATURES="%{?with_rhsm:rhsm}"
+%make_install INSTALL="install -p -c" CARGO_FEATURES="%{?with_rhsm:rhsm} %{?with_rhel9:rhel9}"
 %if %{with ostree_ext}
 make install-ostree-hooks DESTDIR=%{?buildroot}
 %endif