CODEWITHSUNDEEP
node.jsfile-iofsfile-writing
Sterling Butters
Sterling Butters

Reputation: 1175

Node.js: Writing to system files with fs.writeFileSync

I am trying to write to a system file under /sys/kernel/config/usb_gadget with fs.writeFileSync but when writing "" as the contents, the file remains unchanged (with original contents in tact) and results in 

Error: EBUSY: resource busy or locked, write
    at Object.writeSync (fs.js:581:3)
    at Object.writeFileSync (fs.js:1275:26)
    at Socket.<anonymous> (/opt/sterling/ip-kvm-interface/app.js:249:6)
    at Socket.emit (events.js:210:5)
    at /opt/sterling/ip-kvm-interface/node_modules/socket.io/lib/socket.js:528:12
    at processTicksAndRejections (internal/process/task_queues.js:75:11) {
  errno: -16,
  syscall: 'write',
  code: 'EBUSY'
}

when writing some other contents. Permissions for the destination write file are 777.

Is fs.writeFileSync incapable of writing to files under sys or am I missing something else?

Using fsuser /sys/kernel/config/usb_gadget/kvm-gadget/UDC returns nothing (even when Node process is running) and lsof | grep /sys/kernel/config/usb_gadget/kvm-gadget/UDC also returns nothing.

Am I going to have to spawn an echo process to get this to work (not preferred but crossed my mind - since not sure how I would convert it to synchronous task)?

Upvotes: 5

Views: 438

Answers (1)

Sterling Butters
Sterling Butters

Reputation: 1175

https://github.com/nodejs/help/issues/2459

Are there undocumented limitations to fs.writeFileSync that I am unaware of?

Nothing specific to fs.writeFileSync(), you can get the same error with a plain C program.

/sys/kernel/config/usb_gadget is not a real file, it's a communication channel with the kernel's usb gadget driver. It's that driver that is returning the error.

(I could point you to the line of code if you're really interested. It's drivers/usb/gadget/configfs.c in the kernel source tree in any case.)

Upvotes: 4

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