Introduction

Certain devices, like multi media cards (MMC), are appropriately identified by their vendor and product attributes, while others are not. This discrepancy results in some devices being displayed as “Unnamed Drive” within the desktop environment, such as the MATE desktop using Caja. This document aims to provide a detailed method for assigning a name to such devices by implementing an udev rule.

Drive Naming Convention

On the MATE desktop, as well as on other desktop environments and the command line, the name of a drive is typically derived from the product name and the disk label.

In the absence of a disk label, the drive’s size is used instead.

However, if the product name is missing, the disk label will not be displayed; instead, the system defaults to showing the device name (e.g., /dev/mmcblk0).

Shows the renamed device after applying the fix with a changed symbol and the label.

Label Assignment

For demonstration, we use two FAT32 formatted SDHC disks. One is named, and the other is unnamed. Their partition structure is illustrated as follows:

# Output showing disk and partition details
fdisk -l /dev/mmcblk0
Disk /dev/mmcblk0: 7.51 GiB, 8059355136 bytes, 15740928 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
Disklabel type: dos
Disk identifier: 0x68c04c1e

Device         Boot Start      End  Sectors  Size Id Type
/dev/mmcblk0p1       2048 15740927 15738880  7.5G  b W95 FAT32

To set a disk label, execute:

# Read current label:
fatlabel /dev/mmcblk0p1
OLDLABEL
# Set new label:
fatlabel /dev/mmcblk0p1 NEWLABEL

Name Determination

Prior to setting a name, it’s crucial to identify the current name using tools such as udeadm.

Functional Drive

Below is an example of a properly recognized drive, clearly displaying ID_NAME:

# Output showing drive attributes including ID_NAME
udevadm info --query=all --name=/dev/mmcblk0|grep ID_
E: ID_SERIAL=0x002256e1
E: ID_NAME=SU04G
E: ID_PATH=pci-0000:02:00.0-platform-rtsx_pci_sdmmc.0
E: ID_PATH_TAG=pci-0000_02_00_0-platform-rtsx_pci_sdmmc_0
E: ID_PART_TABLE_TYPE=dos
E: ID_DRIVE_FLASH_SD=1
E: ID_DRIVE_MEDIA_FLASH_SD=1

This output presents the product and vendor:

lshw -c disk
...
  *-device
       description: SD Card
       product: SU04G
       vendor: SanDisk
       physical id: e624
       logical name: /dev/mmcblk0
       version: 8.0
       date: 01/2013
       serial: 2250465
       size: 3781MiB (3965MB)
       capabilities: sd partitioned partitioned:dos
       configuration: logicalsectorsize=512 sectorsize=512
...

Problematic Drive

Conversely, here is an instance of a problematic drive lacking ID_NAME:

# Output showing missing ID_NAME
udevadm info --query=all --name=/dev/mmcblk0|grep ID_
E: ID_SERIAL=0x00026ff3
E: ID_PATH=pci-0000:02:00.0-platform-rtsx_pci_sdmmc.0
E: ID_PATH_TAG=pci-0000_02_00_0-platform-rtsx_pci_sdmmc_0
E: ID_PART_TABLE_UUID=68c04c1e
E: ID_PART_TABLE_TYPE=dos
E: ID_DRIVE_FLASH_SD=1
E: ID_DRIVE_MEDIA_FLASH_SD=1

Notice the vendor ‘Unknown (78)’ and the absence of product:

# Output showing device details with missing information
lshw -c disk
...
  *-device
       description: SD Card
       vendor: Unknown (78)
       physical id: 1
       logical name: /dev/mmcblk0
       version: 4.4
       date: 07/2008
       serial: 159731
       size: 7686MiB (8059MB)
       capabilities: sd partitioned partitioned:dos
       configuration: logicalsectorsize=512 sectorsize=512 signature=68c04c1e
...

Remedying the Problematic Drive

Although altering the disk firmware is a potential solution (more feasible for Nvme disks), it’s not a viable option for most SDHC disks. Instead, we can create an udev rule to dynamically assign a name. This is feasible since the required name is present in the E (environment) section.

First, identify unique strings using udevadm:

# For the operational drive:
udevadm info --attribute-walk /dev/mmcblk0|grep -i serial
    ATTRS{serial}=="0x002256e1"
# For the problematic drive:
udevadm info --attribute-walk /dev/mmcblk0|grep -i serial
    ATTRS{serial}=="0x00026ff3"

Create the udev rule:

cd /etc/udev/rules.d
echo\
 'SUBSYSTEM=="block", ATTRS{serial}=="0x00026ff3", ENV{ID_NAME}="SDHC08GB"' >\
 99-custom-disk-name.rules

Apply the rule:

udevadm control --reload-rules
udevadm trigger /dev/mmcblk0

Reinsert the disk to effectuate the changes.

Post-Fix Status of the Problematic Drive

Observe the now-present ID_NAME:

# Output showing the updated ID_NAME
udevadm info --query=all --name=/dev/mmcblk0|grep ID_
E: ID_SERIAL=0x00026ff3
E: ID_PATH=pci-0000:02:00.0-platform-rtsx_pci_sdmmc.0
E: ID_PATH_TAG=pci-0000_02_00_0-platform-rtsx_pci_sdmmc_0
E: ID_PART_TABLE_UUID=68c04c1e
E: ID_PART_TABLE_TYPE=dos
E: ID_DRIVE_FLASH_SD=1
E: ID_DRIVE_MEDIA_FLASH_SD=1
E: ID_NAME=SDHC08GB

Understanding the Hierarchy in Udev

Udev processes information hierarchically. Consequently, the environment and the key ID_NAME are applied multiple times throughout the device tree:

# Hierarchical display of device attributes
udevadm info -t /dev/mmcblk0|egrep -e 'SERIAL|NAME'
  ┆ E: PCI_SLOT_NAME=0000:00:1c.0
    ┆ E: PCI_SLOT_NAME=0000:02:00.0
          ┆ E: MMC_NAME=
            ┆ E: DEVNAME=/dev/mmcblk0
            ┆ E: ID_SERIAL=0x00026ff3
            ┆ E: ID_NAME=SDHC08GB
              ┆ E: DEVNAME=/dev/mmcblk0p1
              ┆ E: ID_SERIAL=0x00026ff3
              ┆ E: ID_NAME=SDHC08GB

Catching ACTION=="add" via the udev rule would propagate ID_NAME to all children of mmcblk0 and itself, when the drive information tree is added. However, upon unmounting a partition, ID_NAME would be removed, rendering ACTION=="add" unsuitable.

To refine the udev rule, consider adding a symbolic link. Unlike a named mmc, an unnamed mmc cannot be accessed via a /dev/ link containing its name. SYMLINK+= could be used for this purpose, but it is not essential for this basic example.

Ansible Playbook

This Ansible playbook is designed to apply specific udev rules across a group of client systems. It focuses on the automation of udev rule deployment for disk naming. The above example is added.

---
- name: Configure udev rules for disk names
  hosts: role_client
  gather_facts: no
  become: yes
  vars:
    ns: udev
  tasks:
    - name: "{{ns}}: Define udev rules"
      ansible.builtin.set_fact:
        udev_rules:
            # 8GB SDHC MMC from Intenso with label ADM-PUB-1
          - 'SUBSYSTEM=="block", ATTRS{serial}=="0x00026ff3", ENV{ID_NAME}="SDHC08GB"'
    - name: "{{ns}}: Create udev rule file"
      ansible.builtin.copy:
        dest: /etc/udev/rules.d/99-custom-disk-name.rules
        content: "{{ udev_rules | join('\n') }}"
        mode: '0644'
      register: udev_rule_file
    - name: "{{ns}}: Reload udev rules"
      ansible.builtin.command:
        cmd: udevadm control --reload-rules
      when: udev_rule_file.changed

History

Version	Date	Notes
0.1.1	2024-03-04	Minor improvements, reformatting 2nd section
0.1.0	2024-03-03	Initial release

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• Last modified (via git): March 04, 2024
• Update 0.1.1 Minor improvements, reformatting 2nd section (e05f5c38)
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