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Use udev for partition UUID #320

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May 11, 2022
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Use udev for partition UUID #320

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Use udev for partition UUID
May 10, 2022
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May 11, 2022
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6 changes: 4 additions & 2 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -546,8 +546,10 @@ Each `ghw.Partition` struct contains these fields:
* `ghw.Partition.Disk` is a pointer to the `ghw.Disk` object associated with
the partition. This will be `nil` if the `ghw.Partition` struct was returned
by the `ghw.DiskPartitions()` library function.
* `ghw.Partition.UUID` is a string containing the volume UUID on Linux, the
partition UUID on MacOS and nothing on Windows.
* `ghw.Partition.UUID` is a string containing the partition UUID on Linux, the
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ok, so for my understanding we are changing from volume UUID to partition UUID? If so, there are practical implications of this change?

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Not really, they are the same uuid afaik, only this is worded weirdly by mentioning volume for some reason. On my local checks, the values given by lsblk were the same as the ones on udev.

I can check further tonight to confirm this.

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thanks, I'll also do my homework and learn a bit more about this area

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@Itxaka Itxaka May 11, 2022 •
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UUID comment seems to confirm that this is indeed the partition UUID, probably the Volume name comes from also adding the MacOS UUID, which is the Volume UUID:

UUID string json:"uuid" // This would be volume UUID on macOS, PartUUID on linux, empty on Windows

And yes, this seems to be the same value as what blkid reports for PARTUUID. Note that there is also a ID_PART_TABLE_UUID which points to the disk UUID, which we should not confuse with this.

And to further confirm that this is indeed the expected value, if you do a low lovel probe with blkid, it will show the actual PART_ENTRY_UUID value, which is mapped by udev to the ID_PART_ENTRY_UUID but for some reason is named different when presented to the user:

$ sudo blkid /dev/nvme0n1p2 --probe
/dev/nvme0n1p2: PART_ENTRY_SCHEME="gpt" PART_ENTRY_UUID="659f38f6-ec95-4e92-88f7-15993d5b3d61" PART_ENTRY_TYPE="21686148-6449-6e6f-744e-656564454649" PART_ENTRY_NUMBER="2" PART_ENTRY_OFFSET="1026048" PART_ENTRY_SIZE="16384" PART_ENTRY_DISK="259:0"

And you can see that matches the actual udev contents:

$ cat /run/udev/data/b259:2|grep ID_PART_ENTRY_UUID    
E:ID_PART_ENTRY_UUID=659f38f6-ec95-4e92-88f7-15993d5b3d61

And output without a low level probe:

$ sudo blkid /dev/nvme0n1p2                        
/dev/nvme0n1p2: PARTUUID="659f38f6-ec95-4e92-88f7-15993d5b3d61"

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thanks @Itxaka this fully makes sense to me. I just need to spend some extra time to learn myself a bit more. I'll review ASAP but in general LGTM (and I totally, really like this direction!)

partition UUID on MacOS and nothing on Windows. On Linux
systems, this is derived from the `ID_PART_ENTRY_UUID` udev entry for the
partition.

```go
package main
Expand Down
36 changes: 7 additions & 29 deletions pkg/block/block_linux.go
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Expand Up @@ -10,7 +10,6 @@ import (
"io"
"io/ioutil"
"os"
"os/exec"
"path/filepath"
"strconv"
"strings"
Expand Down Expand Up @@ -209,7 +208,7 @@ func diskPartitions(ctx *context.Context, paths *linuxpath.Paths, disk string) [
}
size := partitionSizeBytes(paths, disk, fname)
mp, pt, ro := partitionInfo(paths, fname)
du := diskPartUUID(ctx, fname)
du := diskPartUUID(paths, disk, fname)
label := diskPartLabel(paths, disk, fname)
if pt == "" {
pt = diskPartTypeUdev(paths, disk, fname)
Expand Down Expand Up @@ -268,37 +267,16 @@ func diskPartTypeUdev(paths *linuxpath.Paths, disk string, partition string) str
return util.UNKNOWN
}

func diskPartUUID(ctx *context.Context, part string) string {
if !ctx.EnableTools {
ctx.Warn("EnableTools=false disables partition UUID detection.")
return ""
}
if !strings.HasPrefix(part, "/dev") {
part = "/dev/" + part
}
args := []string{
"blkid",
"-s",
"PARTUUID",
part,
}
out, err := exec.Command(args[0], args[1:]...).Output()
func diskPartUUID(paths *linuxpath.Paths, disk string, partition string) string {
info, err := udevInfoPartition(paths, disk, partition)
if err != nil {
ctx.Warn("failed to read disk partuuid of %s : %s\n", part, err.Error())
return ""
}

if len(out) == 0 {
return ""
return util.UNKNOWN
}

parts := strings.Split(string(out), "PARTUUID=")
if len(parts) != 2 {
ctx.Warn("failed to parse the partuuid of %s\n", part)
return ""
if pType, ok := info["ID_PART_ENTRY_UUID"]; ok {
return pType
}

return strings.ReplaceAll(strings.TrimSpace(parts[1]), `"`, "")
return util.UNKNOWN
}

func diskIsRemovable(paths *linuxpath.Paths, disk string) bool {
Expand Down
31 changes: 31 additions & 0 deletions pkg/block/block_linux_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -288,6 +288,37 @@ func TestDiskTypeUdev(t *testing.T) {
}
}

func TestDiskPartUUID(t *testing.T) {
if _, ok := os.LookupEnv("GHW_TESTING_SKIP_BLOCK"); ok {
t.Skip("Skipping block tests.")
}
baseDir, _ := ioutil.TempDir("", "test")
defer os.RemoveAll(baseDir)
ctx := context.New()
ctx.Chroot = baseDir
paths := linuxpath.New(ctx)
partUUID := "11111111-1111-1111-1111-111111111111"

_ = os.MkdirAll(paths.SysBlock, 0755)
_ = os.MkdirAll(paths.RunUdevData, 0755)

// Emulate a disk with one partition with uuid
_ = os.Mkdir(filepath.Join(paths.SysBlock, "sda"), 0755)
_ = os.Mkdir(filepath.Join(paths.SysBlock, "sda", "sda1"), 0755)
_ = ioutil.WriteFile(filepath.Join(paths.SysBlock, "sda", "sda1", "dev"), []byte("259:0\n"), 0644)
_ = ioutil.WriteFile(filepath.Join(paths.RunUdevData, "b259:0"), []byte(fmt.Sprintf("E:ID_PART_ENTRY_UUID=%s\n", partUUID)), 0644)
uuid := diskPartUUID(paths, "sda", "sda1")
if uuid != partUUID {
t.Fatalf("Got uuid %s but expected %s", uuid, partUUID)
}

// Check empty uuid if not found
uuid = diskPartUUID(paths, "sda", "sda2")
if uuid != util.UNKNOWN {
t.Fatalf("Got uuid %s, but expected %s label", uuid, util.UNKNOWN)
}
}

// TestLoopDevicesWithOption tests to see if we find loop devices when the option is activated
func TestLoopDevicesWithOption(t *testing.T) {
if _, ok := os.LookupEnv("GHW_TESTING_SKIP_BLOCK"); ok {
Expand Down