Seperate dracut and dracut-squash compressor for zstd

Previously kexec-tools will pass "--compress zstd" to dracut. It
will make dracut to decide whether: a) call mksquashfs to make a
zstd format squash-root.img, b) call cmd zstd to make a initramfs.

Since dracut(>= 057) has decoupled the compressor for dracut and
dracut-squash, So in this patch, we will pass the compressor seperately.

Note:

The is_squash_available && !dracut_has_option --squash-compressor
&& !is_zsdt_command_available case is left unprocessed on purpose.

Actually, the situation when we want to call zstd compression is:
1) If squash function OK, we want dracut to invoke mksquashfs to make
a zstd format squash-root.img within initramfs.
2) If squash function is not OK, and cmd zstd presents, we want dracut
to invoke cmd zstd to make a zstd format initramfs.

is_zstd_command_available check can handle case 2 completely.

However, for the is_squash_available check, it cannot handle case 1
completely. It only checks if the kernel supports squashfs, it doesn't
check whether the squash module has been added by dracut when making
initramfs. In fact, in kexec-tools we are unable to do the check,
there are multiple ways to forbit dracut to load a module, such as
"dracut -o module" and "omit_dracutmodules in dracut.conf".

When squash dracut module is omitted, is_squash_available check will
still pass, so "--compress zstd" will be appended to dracut cmdline,
and it will call cmd zstd to do the compression. However cmd zstd may
not exist, so it fails.

The previous "--compress zstd" is ambiguous, after the intro of
"--squash-compressor", "--squash-compressor" only effect for
mksquashfs and "--compress" only effect for specific cmd.

So for the is_squash_available && !dracut_has_option
--squash-compressor && !is_zsdt_command_available case, we just leave
it to be handled the default way.

Reviewed-by: Philipp Rudo <prudo@redhat.com>
Signed-off-by: Tao Liu <ltao@redhat.com>

kdump-lib.sh

@@ -37,6 +37,12 @@ is_zstd_command_available()
 	[[ -x "$(command -v zstd)" ]]
 }
 
+dracut_have_option()
+{
+	local _option=$1
+	! dracut "$_option" 2>&1 | grep -q "unrecognized option"
+}
+
 perror_exit()
 {
 	derror "$@"
@@ -448,8 +454,7 @@ is_wdt_active()
 
 have_compression_in_dracut_args()
 {
-	[[ "$(kdump_get_conf_val dracut_args)" =~ \
-		(^|[[:space:]])--(gzip|bzip2|lzma|xz|lzo|lz4|zstd|no-compress|compress)([[:space:]]|$) ]]
+	[[ "$(kdump_get_conf_val dracut_args)" =~ (^|[[:space:]])--(gzip|bzip2|lzma|xz|lzo|lz4|zstd|no-compress|compress|squash-compressor)([[:space:]]|$) ]]
 }
 
 # If "dracut_args" contains "--mount" information, use it

kexec-tools.spec

@@ -64,7 +64,6 @@ Requires: dracut >= 050
 Requires: dracut-network >= 050
 Requires: dracut-squash >= 050
 Requires: ethtool
-Recommends: zstd
 Recommends: grubby
 Recommends: hostname
 BuildRequires: make

mkdumprd

@@ -432,10 +432,9 @@ done <<< "$(kdump_read_conf)"
 handle_default_dump_target
 
 if ! have_compression_in_dracut_args; then
-	# Here zstd is set as the default compression method. If squash module
-	# is available for dracut, libzstd will be used by mksquashfs. If
-	# squash module is unavailable, command zstd will be used instead.
-	if is_squash_available || is_zstd_command_available; then
+	if is_squash_available && dracut_have_option "--squash-compressor"; then
+		add_dracut_arg "--squash-compressor" "zstd"
+	elif is_zstd_command_available; then
 		add_dracut_arg "--compress" "zstd"
 	fi
 fi

mkfadumprd

@@ -64,7 +64,9 @@ fi
 
 # Same as setting zstd in mkdumprd
 if ! have_compression_in_dracut_args; then
-	if is_squash_available || is_zstd_command_available; then
+	if is_squash_available && dracut_have_option "--squash-compressor"; then
+		_dracut_isolate_args+=(--squash-compressor zstd)
+	elif is_zstd_command_available; then
 		_dracut_isolate_args+=(--compress zstd)
 	fi
 fi