sgdisk: Run partx after partition changes

The sgdisk tool does not update the kernel partition table with BLKPG in
contrast to other similar tools but only uses BLKRRPART which fails as
soon as one partition of the disk is mounted.
Update the kernel partition table with partx when we know that a
partition of the disk is in use.

docs/release-notes.md

@@ -10,8 +10,12 @@ nav_order: 9
 
 ### Features
 
+- Support partitioning disk with mounted partitions
+
 ### Changes
 
+- The Dracut module now installs partx
+
 ### Bug fixes
 
 - Fix Akamai Ignition base64 decoding on padded payloads

dracut/30ignition/module-setup.sh

@@ -39,6 +39,7 @@ install() {
         mkfs.fat \
         mkfs.xfs \
         mkswap \
+        partx \
         sgdisk \
         useradd \
         userdel \

internal/distro/distro.go

@@ -36,6 +36,7 @@ var (
 	groupdelCmd  = "groupdel"
 	mdadmCmd     = "mdadm"
 	mountCmd     = "mount"
+	partxCmd     = "partx"
 	sgdiskCmd    = "sgdisk"
 	modprobeCmd  = "modprobe"
 	udevadmCmd   = "udevadm"
@@ -92,6 +93,7 @@ func GroupaddCmd() string  { return groupaddCmd }
 func GroupdelCmd() string  { return groupdelCmd }
 func MdadmCmd() string     { return mdadmCmd }
 func MountCmd() string     { return mountCmd }
+func PartxCmd() string     { return partxCmd }
 func SgdiskCmd() string    { return sgdiskCmd }
 func ModprobeCmd() string  { return modprobeCmd }
 func UdevadmCmd() string   { return udevadmCmd }

internal/exec/stages/disks/partitions.go

@@ -23,6 +23,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"regexp"
 	"sort"
@@ -31,6 +32,7 @@ import (
 
 	cutil "github.com/coreos/ignition/v2/config/util"
 	"github.com/coreos/ignition/v2/config/v3_5_experimental/types"
+	"github.com/coreos/ignition/v2/internal/distro"
 	"github.com/coreos/ignition/v2/internal/exec/util"
 	"github.com/coreos/ignition/v2/internal/sgdisk"
 	iutil "github.com/coreos/ignition/v2/internal/util"
@@ -472,6 +474,10 @@ func (s stage) partitionDisk(dev types.Disk, devAlias string) error {
 		return err
 	}
 
+	var partxAdd []uint64
+	var partxDelete []uint64
+	var partxUpdate []uint64
+
 	for _, part := range resolvedPartitions {
 		shouldExist := partitionShouldExist(part)
 		info, exists := diskInfo.GetPartition(part.Number)
@@ -492,11 +498,13 @@ func (s stage) partitionDisk(dev types.Disk, devAlias string) error {
 		case !exists && shouldExist:
 			op.CreatePartition(part)
 			modification = true
+			partxAdd = append(partxAdd, uint64(part.Number))
 		case exists && !shouldExist && !wipeEntry:
 			return fmt.Errorf("partition %d exists but is specified as nonexistant and wipePartitionEntry is false", part.Number)
 		case exists && !shouldExist && wipeEntry:
 			op.DeletePartition(part.Number)
 			modification = true
+			partxDelete = append(partxDelete, uint64(part.Number))
 		case exists && shouldExist && matches:
 			s.Logger.Info("partition %d found with correct specifications", part.Number)
 		case exists && shouldExist && !wipeEntry && !matches:
@@ -510,6 +518,7 @@ func (s stage) partitionDisk(dev types.Disk, devAlias string) error {
 				part.StartSector = &info.StartSector
 				op.CreatePartition(part)
 				modification = true
+				partxUpdate = append(partxUpdate, uint64(part.Number))
 			} else {
 				return fmt.Errorf("Partition %d didn't match: %v", part.Number, matchErr)
 			}
@@ -518,6 +527,7 @@ func (s stage) partitionDisk(dev types.Disk, devAlias string) error {
 			op.DeletePartition(part.Number)
 			op.CreatePartition(part)
 			modification = true
+			partxUpdate = append(partxUpdate, uint64(part.Number))
 		default:
 			// unfortunatey, golang doesn't check that all cases are handled exhaustively
 			return fmt.Errorf("Unreachable code reached when processing partition %d. golang--", part.Number)
@@ -532,6 +542,30 @@ func (s stage) partitionDisk(dev types.Disk, devAlias string) error {
 		return fmt.Errorf("commit failure: %v", err)
 	}
 
+	// In contrast to similar tools, sgdisk does not trigger the update of the
+	// kernel partition table with BLKPG but only uses BLKRRPART which fails
+	// as soon as one partition of the disk is mounted
+	if len(activeParts) > 0 {
+		runPartxCommand := func(op string, partitions []uint64) error {
+			for _, partNr := range partitions {
+				cmd := exec.Command(distro.PartxCmd(), "--"+op, "--nr", strconv.FormatUint(partNr, 10), blockDevResolved)
+				if _, err := s.Logger.LogCmd(cmd, "triggering partition %d %s on %q", partNr, op, devAlias); err != nil {
+					return fmt.Errorf("partition %s failed: %v", op, err)
+				}
+			}
+			return nil
+		}
+		if err := runPartxCommand("delete", partxDelete); err != nil {
+			return err
+		}
+		if err := runPartxCommand("update", partxUpdate); err != nil {
+			return err
+		}
+		if err := runPartxCommand("add", partxAdd); err != nil {
+			return err
+		}
+	}
+
 	// It's best to wait here for the /dev/ABC entries to be
 	// (re)created, not only for other parts of the initramfs but
 	// also because s.waitOnDevices() can still race with udev's