mkdumprd: basic support for btrfs subvol

The kdump scripts previously could not correctly handle cases where the
dump target was located on a btrfs subvolume. The logic for finding
the mount point did not account for the way subvolumes are represented,
leading to failures in identifying the target device and checking for
available space.

This patch introduces support for btrfs subvolumes by:

1.  Adding a new helper function `get_btrfs_subvol_from_mntopt` to
    extract the subvolume name from mount options.
2.  Modifying `get_mntpoint_from_target` to accept a subvolume
    name. When a subvolume is provided, it correctly identifies the
    mount point by looking for the source entry that includes the
    subvolume name (e.g., `/dev/sda1[/subvol]`).
3.  Updating various functions in `mkdumprd`, `kdump-lib.sh`, and the
    dracut module setup scripts to detect if the target is on a btrfs
    filesystem, parse the subvolume, and pass it to the relevant
    functions for mount point resolution and free space checks.

This ensures that kdump can now be reliably configured with a dump
target located on a btrfs subvolume.

Signed-off-by: Lichen Liu <[email protected]>

Author: licliu

dracut/99kdumpbase/module-setup.sh

@@ -683,16 +683,21 @@ kdump_install_pre_post_conf() {
 }
 
 default_dump_target_install_conf() {
-    local _target _fstype
+    local _target _fstype _subvol _options
     local _mntpoint _save_path
 
     is_user_configured_dump_target && return
 
     _save_path=$(get_bind_mount_source "$(get_save_path)")
     _target=$(get_target_from_path "$_save_path")
-    _mntpoint=$(get_mntpoint_from_target "$_target")
-
+    _options=$(get_mount_info OPTIONS target "$_save_path" -f)
     _fstype=$(get_fs_type_from_target "$_target")
+    if [[ $_fstype == btrfs ]]; then
+        _subvol=$(get_btrfs_subvol_from_mntopt "$_options")
+    fi
+
+    _mntpoint=$(get_mntpoint_from_target "$_target" "$_subvol")
+
     if is_fs_type_nfs "$_fstype"; then
         kdump_collect_netif_usage "$_target"
         _fstype="nfs"

kdump-lib-initramfs.sh

@@ -110,15 +110,29 @@ get_fs_type_from_target()
 
 get_mntpoint_from_target()
 {
-	# get the first TARGET when SOURCE doesn't end with ].
-	# In most cases, a SOURCE ends with ] when fsroot or subvol exists.
-	_mntpoint=$(get_mount_info TARGET,SOURCE source "$1" | grep -v "\]$" | awk 'NR==1 { print $1 }')
-
+	_subvol="$2"
+	if [ -z "$_subvol" ]; then
+		# get the first TARGET when SOURCE doesn't end with ].
+		# In most cases, a SOURCE ends with ] when fsroot or subvol exists.
+		_mntpoint=$(get_mount_info TARGET,SOURCE source "$1" | grep -v "\]$" | awk 'NR==1 { print $1 }')
+	else
+		# btrfs with subvol
+		_mntpoint=$(get_mount_info TARGET,SOURCE source "$1" | grep "\[$_subvol\]$" | awk 'NR==1 { print $1 }')
+	fi
 	# fallback to the old way when _mntpoint is empty.
 	[ -n "$_mntpoint" ] || _mntpoint=$(get_mount_info TARGET source "$1" -f)
 	echo "$_mntpoint"
 }
 
+get_btrfs_subvol_from_mntopt()
+{
+	_subvol=${1#*subvol=}
+	# mount option may not contain subvol
+	[ "$1" != "$_subvol" ] || return 0
+	_subvol=${_subvol%%,*}
+	echo "$_subvol"
+}
+
 is_ssh_dump_target()
 {
 	kdump_get_conf_val ssh | grep -q @

kdump-lib.sh

@@ -177,7 +177,7 @@ get_kdump_targets()
 # part is the bind mounted directory which quotes by bracket "[]".
 get_bind_mount_source()
 {
-	local _mnt _path _src _opt _fstype
+	local _mnt _path _src _opt _fstype _subvol
 	local _fsroot _src_nofsroot
 
 	_mnt=$(df "$1" | tail -1 | awk '{print $NF}')
@@ -200,15 +200,13 @@ get_bind_mount_source()
 
 	_fsroot=${_src#"${_src_nofsroot}"[}
 	_fsroot=${_fsroot%]}
-	_mnt=$(get_mntpoint_from_target "$_src_nofsroot")
-
 	# for btrfs, _fsroot will also contain the subvol value as well, strip it
 	if [[ $_fstype == btrfs ]]; then
-		local _subvol
-		_subvol=${_opt#*subvol=}
-		_subvol=${_subvol%,*}
+		_subvol=$(get_btrfs_subvol_from_mntopt "$_opt")
 		_fsroot=${_fsroot#"$_subvol"}
 	fi
+	_mnt=$(get_mntpoint_from_target "$_src_nofsroot" "$_subvol")
+
 	echo "$_mnt$_fsroot$_path"
 }
 
@@ -219,11 +217,12 @@ get_mntopt_from_target()
 
 # Get the path where the target will be mounted in kdump kernel
 # $1: kdump target device
+# $2: btrfs subvol
 get_kdump_mntpoint_from_target()
 {
 	local _mntpoint
 
-	_mntpoint=$(get_mntpoint_from_target "$1")
+	_mntpoint=$(get_mntpoint_from_target "$1" "$2")
 	# mount under /sysroot if dump to root disk or mount under
 	# mount under /kdumproot if dump target is not mounted in first kernel
 	# mount under /kdumproot/$_mntpoint in other cases in 2nd kernel.

mkdumprd

@@ -76,10 +76,13 @@ to_mount()
 {
 	local _target=$1 _fstype=$2 _options=$3 _sed_cmd _new_mntpoint _pdev
 
-	_new_mntpoint=$(get_kdump_mntpoint_from_target "$_target")
 	_fstype="${_fstype:-$(get_fs_type_from_target "$_target")}"
 	_options="${_options:-$(get_mntopt_from_target "$_target")}"
 	_options="${_options:-defaults}"
+	if [[ $_fstype == btrfs ]]; then
+		_subvol=$(get_btrfs_subvol_from_mntopt "$_options")
+	fi
+	_new_mntpoint=$(get_kdump_mntpoint_from_target "$_target" "$_subvol")
 
 	if [[ $_fstype == "nfs"* ]]; then
 		_pdev=$_target
@@ -146,7 +149,7 @@ mkdir_save_path_ssh()
 #$1=dump target
 get_fs_size()
 {
-	df --output=avail "$(get_mntpoint_from_target "$1")/$SAVE_PATH" | tail -1
+	df --output=avail "$(get_mntpoint_from_target "$1" "$2")/$SAVE_PATH" | tail -1
 }
 
 #Function: get_raw_size
@@ -159,6 +162,7 @@ get_raw_size()
 #Function: check_size
 #$1: dump type string ('raw', 'fs', 'ssh')
 #$2: dump target
+#$3: btrfs subvol
 check_size()
 {
 	local avail memtotal
@@ -172,7 +176,7 @@ check_size()
 		avail=$(get_ssh_size "$2")
 		;;
 	fs)
-		avail=$(get_fs_size "$2")
+		avail=$(get_fs_size "$2" "$3")
 		;;
 	*)
 		return
@@ -302,20 +306,24 @@ add_mount()
 #handle the case user does not specify the dump target explicitly
 handle_default_dump_target()
 {
-	local _target
-	local _mntpoint
+	local _target _mntpoint _fstype _subvol _options
 
 	is_user_configured_dump_target && return
 
 	check_save_path_fs "$SAVE_PATH"
 
 	_save_path=$(get_bind_mount_source "$SAVE_PATH")
+	_options=$(get_mount_info OPTIONS target "$_save_path" -f)
 	_target=$(get_target_from_path "$_save_path")
-	_mntpoint=$(get_mntpoint_from_target "$_target")
+	_fstype=$(get_fs_type_from_target "$_target")
+	if [[ $_fstype == btrfs ]]; then
+		_subvol=$(get_btrfs_subvol_from_mntopt "$_options")
+	fi
 
+	_mntpoint=$(get_mntpoint_from_target "$_target" "$_subvol")
 	SAVE_PATH=${_save_path##"$_mntpoint"}
-	add_mount "$_target"
-	check_size fs "$_target"
+	add_mount "$_target" "$_fstype" "$_options"
+	check_size fs "$_target" "$_subvol"
 }
 
 # firstly get right SSH_KEY_LOCATION