make: Add optional LZ4 support

Memory page compression requires liblz4, but making it mandatory would
prevent CRIU from building on systems that do not provide it.

Detect liblz4 with pkg-config and enable CONFIG_LZ4 only when it is
available. Add NO_LZ4=1 as an explicit opt-out and register the
development package in the supported distribution dependency lists.
Install liblz4 for the per-commit build, then run a separate NO_LZ4
build and unit test to keep the optional configuration usable.

Assisted-by: Codex:GPT-5
Signed-off-by: Radostin Stoyanov <rstoyanov@fedoraproject.org>

.github/workflows/check-commits.yml

@@ -19,7 +19,7 @@ jobs:
         # Checkout pull request HEAD commit instead of merge commit
         ref: ${{ github.event.pull_request.head.sha }}
     - name: Install dependencies
-      run: sudo contrib/apt-install libprotobuf-dev libprotobuf-c-dev protobuf-c-compiler protobuf-compiler python3-protobuf libnl-3-dev libnet-dev libcap-dev uuid-dev
+      run: sudo contrib/apt-install libprotobuf-dev libprotobuf-c-dev protobuf-c-compiler protobuf-compiler python3-protobuf libnl-3-dev libnet-dev libcap-dev uuid-dev liblz4-dev
     - name: Configure git user details
       run: |
         git config --global user.email "checkpoint-restore@users.noreply.github.com"
@@ -28,3 +28,8 @@ jobs:
       run: git fetch origin ${{ github.base_ref }}:${{ github.base_ref }}
     - name: Build each commit
       run: git rebase ${{ github.base_ref }} -x "make -C scripts/ci check-commit"
+    - name: Build without LZ4
+      run: |
+        make mrproper
+        make -j "$(nproc)" NO_LZ4=1
+        make unittest NO_LZ4=1

Makefile

@@ -237,6 +237,7 @@ else
 export CONFIG_COMPAT := y
 export CONFIG_GNUTLS := y
 export CONFIG_HAS_LIBBPF := y
+export CONFIG_LZ4 := y
 endif
 
 #

Makefile.config

@@ -46,6 +46,14 @@ else
         $(info $S      Install gnutls-devel (RPM) or gnutls-dev (DEB) to fix.)
 endif
 
+ifeq ($(NO_LZ4)x$(call pkg-config-check,liblz4),xy)
+        LIBS_FEATURES	+= -llz4
+        export CONFIG_LZ4 := y
+        FEATURE_DEFINES	+= -DCONFIG_LZ4
+else
+        $(info Note: Building without LZ4 compression support.)
+endif
+
 ifeq ($(call pkg-config-check,libnftables),y)
         LIB_NFTABLES	:= $(shell $(PKG_CONFIG) --libs libnftables)
         ifeq ($(call try-cc,$(FEATURE_TEST_NFTABLES_LIB_API_0),$(LIB_NFTABLES)),true)

contrib/dependencies/apk-packages.sh

@@ -19,6 +19,7 @@ apk add --no-cache \
 	libcap-dev \
 	libcap-utils \
 	libdrm-dev \
+	lz4-dev \
 	libnet-dev \
 	libnl3-dev \
 	libtraceevent-dev \

contrib/dependencies/apt-cross-packages.sh

@@ -18,6 +18,7 @@ fi
 	libelf-dev:"${DEBIAN_ARCH}" \
 	libexpat1-dev:"${DEBIAN_ARCH}" \
 	libgnutls28-dev:"${DEBIAN_ARCH}" \
+	liblz4-dev:"${DEBIAN_ARCH}" \
 	libnet-dev:"${DEBIAN_ARCH}" \
 	libnftables-dev:"${DEBIAN_ARCH}" \
 	libnl-3-dev:"${DEBIAN_ARCH}" \

contrib/dependencies/apt-packages.sh

@@ -23,6 +23,7 @@ fi
 	libelf-dev \
 	libgnutls28-dev \
 	libgnutls30 \
+	liblz4-dev \
 	libnet-dev \
 	libnl-3-dev \
 	libnl-route-3-dev \

contrib/dependencies/dnf-packages.sh

@@ -17,6 +17,7 @@ dnf install -y \
 	libbsd-devel \
 	libcap-devel \
 	libdrm-devel \
+	lz4-devel \
 	libnet-devel \
 	libnl3-devel \
 	libselinux-devel \

contrib/dependencies/pacman-packages.sh

@@ -15,6 +15,7 @@ pacman -Syu --noconfirm \
 	libbsd \
 	libcap \
 	libdrm \
+	lz4 \
 	libelf \
 	libnet \
 	libnl \