feat(dracut.sh): add "--cpio-reflink" option for calling dracut-cpio

The new dracut-cpio binary is capable of performing copy-on-write
optimized initramfs archive creation, but due to the rust dependency
isn't built / installed by default.
This change adds a new "--cpio-reflink" parameter for dracut which
sees dracut-cpio called for archive creation instead of GNU cpio.

Signed-off-by: David Disseldorp <[email protected]>

Author: ddiss

dracut.sh

@@ -226,6 +226,7 @@ Creates initial ramdisk images for preloading modules
                          otherwise you will not be able to boot.
   --no-compress         Do not compress the generated initramfs.  This will
                          override any other compression options.
+  --cpio-reflink        Attempt to reflink cpio file data using dracut-cpio.
   --list-modules        List all available dracut modules.
   -M, --show-modules    Print included module's name to standard output during
                          build.
@@ -412,6 +413,7 @@ rearrange_params() {
             --long zstd \
             --long no-compress \
             --long gzip \
+            --long cpio-reflink \
             --long list-modules \
             --long show-modules \
             --long keep \
@@ -770,6 +772,7 @@ while :; do
         --zstd) compress_l="zstd" ;;
         --no-compress) _no_compress_l="cat" ;;
         --gzip) compress_l="gzip" ;;
+        --cpio-reflink) cpio_reflink="yes" ;;
         --list-modules) do_list="yes" ;;
         -M | --show-modules)
             show_modules_l="yes"
@@ -1151,6 +1154,17 @@ trap 'exit 1;' SIGINT
 readonly initdir="${DRACUT_TMPDIR}/initramfs"
 mkdir -p "$initdir"
 
+if [[ $cpio_reflink == "yes" ]]; then
+    dracut_cpio="$dracutbasedir/dracut-cpio"
+    if [[ -x $dracut_cpio ]]; then
+        # align based on statfs optimal transfer size
+        cpio_align=$(stat --file-system -c "%s" -- "$initdir")
+    else
+        dinfo "cpio-reflink ignored due to lack of dracut-cpio"
+        unset cpio_reflink
+    fi
+fi
+
 # shellcheck disable=SC2154
 if [[ $early_microcode == yes ]] || { [[ $acpi_override == yes ]] && [[ -d $acpi_table_dir ]]; }; then
     readonly early_cpio_dir="${DRACUT_TMPDIR}/earlycpio"
@@ -2252,6 +2266,8 @@ if dracut_module_included "squash"; then
 fi
 
 if [[ $do_strip == yes ]] && ! [[ $DRACUT_FIPS_MODE ]]; then
+    # warn that stripping files negates (dedup) benefits of using reflink
+    [ -n "$cpio_reflink" ] && dinfo "inefficient: strip is enabled alongside cpio reflink"
     dinfo "*** Stripping files ***"
     find "$initdir" -type f \
         -executable -not -path '*/lib/modules/*.ko' -print0 \
@@ -2322,15 +2338,29 @@ if [[ $create_early_cpio == yes ]]; then
     fi
 
     # The microcode blob is _before_ the initramfs blob, not after
-    if ! (
-        umask 077
-        cd "$early_cpio_dir/d"
-        find . -print0 | sort -z \
-            | cpio ${CPIO_REPRODUCIBLE:+--reproducible} --null \
-                ${cpio_owner:+-R "$cpio_owner"} -H newc -o --quiet > "${DRACUT_TMPDIR}/initramfs.img"
-    ); then
-        dfatal "dracut: creation of $outfile failed"
-        exit 1
+    if [[ -n $cpio_reflink ]]; then
+        if ! (
+            umask 077
+            cd "$early_cpio_dir/d"
+            find . -print0 | sort -z \
+                | $dracut_cpio --null ${cpio_owner:+--owner "$cpio_owner"} \
+                    --mtime 0 --data-align "$cpio_align" --truncate-existing \
+                    "${DRACUT_TMPDIR}/initramfs.img"
+        ); then
+            dfatal "dracut: creation of reflinked $outfile failed"
+            exit 1
+        fi
+    else
+        if ! (
+            umask 077
+            cd "$early_cpio_dir/d"
+            find . -print0 | sort -z \
+                | cpio ${CPIO_REPRODUCIBLE:+--reproducible} --null \
+                    ${cpio_owner:+-R "$cpio_owner"} -H newc -o --quiet > "${DRACUT_TMPDIR}/initramfs.img"
+        ); then
+            dfatal "dracut: creation of $outfile failed"
+            exit 1
+        fi
     fi
 fi
 
@@ -2381,15 +2411,31 @@ case $compress in
         ;;
 esac
 
-if ! (
-    umask 077
-    cd "$initdir"
-    find . -print0 | sort -z \
-        | cpio ${CPIO_REPRODUCIBLE:+--reproducible} --null ${cpio_owner:+-R "$cpio_owner"} -H newc -o --quiet \
-        | $compress >> "${DRACUT_TMPDIR}/initramfs.img"
-); then
-    dfatal "dracut: creation of $outfile failed"
-    exit 1
+if [[ -n $cpio_reflink && $compress == "cat" ]]; then
+    # dracut-cpio appends by default, so any ucode remains
+    if ! (
+        umask 077
+        cd "$initdir"
+        find . -print0 | sort -z \
+            | $dracut_cpio --null ${cpio_owner:+--owner "$cpio_owner"} \
+                --mtime 0 --data-align "$cpio_align" \
+                "${DRACUT_TMPDIR}/initramfs.img"
+    ); then
+        dfatal "dracut: creation of reflinked $outfile failed"
+        exit 1
+    fi
+else
+    [ -n "$cpio_reflink" ] && dinfo "cpio-reflink ignored due to compression"
+    if ! (
+        umask 077
+        cd "$initdir"
+        find . -print0 | sort -z \
+            | cpio ${CPIO_REPRODUCIBLE:+--reproducible} --null ${cpio_owner:+-R "$cpio_owner"} -H newc -o --quiet \
+            | $compress >> "${DRACUT_TMPDIR}/initramfs.img"
+    ); then
+        dfatal "dracut: creation of $outfile failed"
+        exit 1
+    fi
 fi
 
 # shellcheck disable=SC2154

man/dracut.8.asc

@@ -530,6 +530,15 @@ will not be able to boot.
     Specifies the kernel image, which to include in the UEFI executable. The default is
     _/lib/modules/<KERNEL-VERSION>/vmlinuz_ or _/boot/vmlinuz-<KERNEL-VERSION>_
 
+**--cpio-reflink**::
+    Attempt to use the dracut-cpio binary, which optimizes archive creation for
+    copy-on-write filesystems by using the copy_file_range(2) syscall via Rust's
+    io::copy(). When specified, initramfs archives are also padded to ensure
+    optimal data alignment for extent sharing. To retain reflink data
+    deduplication benefits, this should be used alongside the **--no-compress**
+    and **--no-strip** parameters, with initramfs source files, **--tmpdir**
+    staging area and destination all on the same copy-on-write capable filesystem.
+
 ENVIRONMENT
 -----------
 

shell-completion/bash/dracut

@@ -32,7 +32,8 @@ _dracut() {
             --local --hostonly --no-hostonly --fstab --help --bzip2 --lzma
             --xz --zstd --no-compress --gzip --list-modules --show-modules --keep
             --printsize --regenerate-all --noimageifnotneeded --early-microcode
-            --no-early-microcode --print-cmdline --reproducible --uefi'
+            --no-early-microcode --print-cmdline --reproducible --uefi
+            --cpio-reflink'
         [ARG]='-a -m -o -d -I -k -c -L --kver --add --force-add --add-drivers
             --omit-drivers --modules --omit --drivers --filesystems --install
             --fwdir --libdirs --fscks --add-fstab --mount --device --nofscks