如何配置libnfc使用通过udev规则固定命名的NFC设备？

Great job setting up those udev rules for fixed device names—this is exactly the right approach to avoid the frustrating device number shuffle! Let’s get libnfc hooked up to your /dev/nfc_a and /dev/nfc_b devices with these straightforward steps:

1. Locate the libnfc Configuration File #

First, find where libnfc stores its config. Most systems use either:

• System-wide config: /etc/nfc/libnfc.conf (create the /etc/nfc directory if it doesn’t exist)
• User-specific config: ~/.config/nfc/libnfc.conf (ideal for per-user customizations)

2. Option 1: Set a Default Fixed Device #

If you want one reader to be the default for all libnfc commands, edit the config file and adjust the device.name line:

# Comment out any existing device.name lines
# device.name = "usb:072f:2200"

# Add your fixed device path
device.name = "/dev/nfc_a"

To switch to the second reader temporarily, you’ll just pass the device path as a command-line argument (more on that below).

3. Option 2: Configure Named Device Aliases (More Flexible) #

For easy switching between readers without typing full paths, define aliases in the config file. First, you’ll need to know your reader’s connection string prefix (e.g., pn532_uart for UART-connected readers, pn532_usb for USB). You can get this by running nfc-list when the reader is connected (look for lines like connstring: pn532_uart:/dev/ttyUSB0).

Add these blocks to your config:

[nfc_a]
name = "Top-Left NFC Reader"
connstring = "pn532_uart:/dev/nfc_a"

[nfc_b]
name = "Top-Right NFC Reader"
connstring = "pn532_uart:/dev/nfc_b"

Now you can reference them by alias in commands:

nfc-list -d nfc_a
nfc-poll -d nfc_b

4. Directly Specify the Device in Commands or Code #

If you don’t want to edit the config file, you can always pass the fixed device path directly to libnfc tools:

# Check the left reader
nfc-list -d /dev/nfc_a

# Poll the right reader for tags
nfc-poll -d /dev/nfc_b

For custom code using the libnfc C API, pass the device path or alias to nfc_open():

nfc_device *pnd;
nfc_context *context;

nfc_init(&context);
// Open the fixed device
pnd = nfc_open(context, "/dev/nfc_a");
// Or open by alias
// pnd = nfc_open(context, "nfc_b");

5. Verify Permissions (Common Gotcha!) #

Make sure your user account has access to the /dev/nfc_a and /dev/nfc_b devices. Typically, these devices belong to the dialout or plugdev group. Add yourself to the correct group with:

sudo usermod -aG dialout $USER

Log out and back in for the group change to take effect.

Test It Out #

Run nfc-list with your preferred device specifier—you should see the reader’s info without any "device not found" errors. If something’s off, double-check your udev rules are creating the symlinks correctly (run ls -l /dev/nfc* to confirm) and that your connstring prefix matches your reader type.

内容的提问来源于stack exchange，提问作者Rene Auberger