sfdisk: add sfdisk module with 'pretend' support

This is a copy of sgdisk, with mapping around sfdisk tooling.
Update the buildOptions to understand sfdisk requirements and
focus on adding support for the pretend function.

Fixes: https://issues.redhat.com/browse/COS-2837

Author: prestist

config/shared/errors/errors.go

@@ -87,6 +87,8 @@ var (
 	ErrPathConflictsSystemd      = errors.New("path conflicts with systemd unit or dropin")
 	ErrCexWithClevis             = errors.New("cannot use cex with clevis")
 	ErrCexWithKeyFile            = errors.New("cannot use key file with cex")
+	ErrBadSfdiskPretend          = errors.New("sfdisk had unexpected output while pretending partition configuration on device")
+	ErrBadSfdiskCommit           = errors.New("sfdisk had unexpected output while committing partition configuration to device")
 
 	// Systemd section errors
 	ErrInvalidSystemdExt       = errors.New("invalid systemd unit extension")

internal/exec/stages/disks/partitions.go

@@ -30,6 +30,7 @@ import (
 	"strconv"
 	"strings"
 
+	sharedErrors "github.com/coreos/ignition/v2/config/shared/errors"
 	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"
@@ -177,7 +178,7 @@ func (s stage) getRealStartAndSize(dev types.Disk, devAlias string, diskInfo uti
 		return nil, err
 	}
 
-	realDimensions, err := parseSgdiskPretend(output, partitionsToInspect)
+	realDimensions, err := parseSfdiskPretend(output, partitionsToInspect)
 	if err != nil {
 		return nil, err
 	}
@@ -284,6 +285,64 @@ func parseSgdiskPretend(sgdiskOut string, partitionNumbers []int) (map[int]sgdis
 	return output, nil
 }
 
+type sfdiskOutput struct {
+	start int64
+	size  int64
+}
+
+// ParsePretend takes the output from sfdisk running with the argument --no-act. Similar to sgdisk
+// it then uses regex to parse the output into understood values like 'start' 'size' and attempts
+// to catch any failures and wrap them to return to the caller.
+func parseSfdiskPretend(sfdiskOut string, partitionNumbers []int) (map[int]sfdiskOutput, error) {
+	if len(partitionNumbers) == 0 {
+		return nil, nil
+	}
+
+	// Prepare the data, and a regex for matching on partitions
+	partitionRegex := regexp.MustCompile(`^/dev/\S+\s+\S*\s+(\d+)\s+(\d+)\s+\d+\s+\S+\s+\S+\s+\S+.*$`)
+	output := map[int]sfdiskOutput{}
+	current := sfdiskOutput{}
+	i := 0
+	lines := strings.Split(sfdiskOut, "\n")
+	for _, line := range lines {
+		matches := partitionRegex.FindStringSubmatch(line)
+
+		// Sanity check number of partition entries
+		if i > len(partitionNumbers) {
+			return nil, sharedErrors.ErrBadSfdiskPretend
+		}
+
+		// Verify that we are not reading a 'failed' or 'error'
+		errorRegex := regexp.MustCompile(`(?i)(failed|error)`)
+		if errorRegex.MatchString(line) {
+			return nil, fmt.Errorf("%w: sfdisk returned :%v", sharedErrors.ErrBadSfdiskPretend, line)
+		}
+
+		// When we get a match it should be
+		// Whole line at [0]
+		// Start at [1]
+		// Size at [2]
+		if len(matches) > 1 {
+			start, err := strconv.Atoi(matches[1])
+			if err != nil {
+				return nil, err
+			}
+			end, err := strconv.Atoi(matches[2])
+			if err != nil {
+				return nil, err
+			}
+
+			current.start = int64(start)
+			// Add one due to overlap
+			current.size = int64(end - start + 1)
+			output[partitionNumbers[i]] = current
+			i++
+		}
+	}
+
+	return output, nil
+}
+
 // partitionShouldExist returns whether a bool is indicating if a partition should exist or not.
 // nil (unspecified in json) is treated the same as true.
 func partitionShouldExist(part sgdisk.Partition) bool {

internal/exec/stages/disks/partitions_test.go

@@ -0,0 +1,106 @@
+package disks
+
+import (
+	"errors"
+	"reflect"
+	"testing"
+
+	internalErrors "github.com/coreos/ignition/v2/config/shared/errors"
+)
+
+func TestPartitionParse(t *testing.T) {
+	// Define test cases
+	tests := []struct {
+		name             string
+		sfdiskOut        string
+		partitionNumbers []int
+		expectedOutput   map[int]sfdiskOutput
+		expectedError    error
+	}{
+		{
+			name: "valid input with single partition",
+			sfdiskOut: `
+Disk /dev/vda: 2 GiB, 2147483648 bytes, 4194304 sectors
+Units: sectors of 1 * 512 = 512 bytes
+Sector size (logical/physical): 512 bytes / 512 bytes
+I/O size (minimum/optimal): 512 bytes / 512 bytes
+
+>>> Created a new DOS (MBR) disklabel with disk identifier 0x501fc254.
+/dev/vda1: Created a new partition 1 of type 'Linux' and of size 5 KiB.
+/dev/vda2: Done.
+
+New situation:
+Disklabel type: dos
+Disk identifier: 0x501fc254
+
+Device     Boot Start   End Sectors Size Id Type
+/dev/vda1        2048  2057      10   5K 83 Linux
+The partition table is unchanged (--no-act).`,
+			partitionNumbers: []int{1},
+			expectedOutput: map[int]sfdiskOutput{
+				1: {start: 2048, size: 10},
+			},
+			expectedError: nil,
+		},
+		{
+			name: "valid input with two partitions",
+			sfdiskOut: `
+Disk /dev/vda: 2 GiB, 2147483648 bytes, 4194304 sectors
+Units: sectors of 1 * 512 = 512 bytes
+Sector size (logical/physical): 512 bytes / 512 bytes
+I/O size (minimum/optimal): 512 bytes / 512 bytes
+
+>>> Created a new DOS (MBR) disklabel with disk identifier 0x8d8dd38c.
+/dev/vda1: Created a new partition 1 of type 'Linux' and of size 5 KiB.
+/dev/vda2: Created a new partition 2 of type 'Linux' and of size 5 KiB.
+/dev/vda3: Done.
+
+New situation:
+Disklabel type: dos
+Disk identifier: 0x8d8dd38c
+
+Device     Boot Start   End Sectors Size Id Type
+/dev/vda1        2048  2057      10   5K 83 Linux
+/dev/vda2        4096  4105      10   5K 83 Linux
+The partition table is unchanged (--no-act).`,
+			partitionNumbers: []int{1, 2},
+			expectedOutput: map[int]sfdiskOutput{
+				1: {start: 2048, size: 10},
+				2: {start: 4096, size: 10},
+			},
+			expectedError: nil,
+		},
+		{
+			name: "invalid input with 1 partition starting on sector 0",
+			sfdiskOut: `
+Disk /dev/vda: 2 GiB, 2147483648 bytes, 4194304 sectors
+Units: sectors of 1 * 512 = 512 bytes
+Sector size (logical/physical): 512 bytes / 512 bytes
+I/O size (minimum/optimal): 512 bytes / 512 bytes
+
+>>> Created a new DOS (MBR) disklabel with disk identifier 0xdebbe997.
+/dev/vda1: Start sector 0 out of range.
+Failed to add #1 partition: Numerical result out of range
+Leaving.
+`,
+			partitionNumbers: []int{1},
+			expectedOutput: map[int]sfdiskOutput{
+				1: {start: 0, size: 0},
+			},
+			expectedError: internalErrors.ErrBadSfdiskPretend,
+		},
+	}
+
+	for i, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			output, err := parseSfdiskPretend(tt.sfdiskOut, tt.partitionNumbers)
+			if tt.expectedError != nil {
+				if !errors.Is(err, tt.expectedError) {
+					t.Errorf("#%d: bad error: result = %v, expected = %v", i, err, tt.expectedError)
+				}
+			} else if !reflect.DeepEqual(output, tt.expectedOutput) {
+				t.Errorf("#%d: result = %v, expected = %v", i, output, tt.expectedOutput)
+			}
+		})
+	}
+}