accessing files in virtual filesystems like /sys on linux without having to set --allow-all permissions

[nirjan-dev]

version info

deno 2.1.4 (stable, release, x86_64-unknown-linux-gnu)
v8 13.0.245.12-rusty
typescript 5.6.2

context

I'm trying to create a home lab server monitoring app with Deno so I need to grab some system metrics. I found a library which gives me APIs to access system metrics which aren't provided my native Deno APIs. I'm trying to access the battery info but it's not working if I don't use --allow-all permissions. This is because the library is basically reading this file on linux: /sys/class/power_supply/BAT0/uevent. So, giving just read permission for that file doesn't seem to work (I suspect because it's inside a virtual filesystem but I don't have enough linux expertise to be certain).

limited replication

Try running this code without giving --allow-all permission acces

const batteryStatsRaw = await Deno.readFile(
    `/sys/class/power_supply/BAT0/uevent`
  );

  const powerStatsText = await new TextDecoder().decode(batteryStatsRaw);

  console.log(powerStatsText);

error messages

I get this error message when it tries to read that file (works fine if I do --allow-all)

error: Uncaught (in promise) NotCapable: Requires all access to "/sys/class/power_supply/BAT0/uevent", specify the required permissions during compilation using `deno compile --allow-all`
    at Object.readFile (ext:deno_fs/30_fs.js:753:24)
    at getBatteryStats (file:///tmp/deno-compile-agent/server-monitor-app/agent/main.ts:32:39)
    at Object.runMicrotasks (ext:core/01_core.js:683:26)
    at Array.processTicksAndRejections (ext:deno_node/_next_tick.ts:59:10)
    at eventLoopTick (ext:core/01_core.js:172:29)
    at async getMetrics (file:///tmp/deno-compile-agent/server-monitor-app/agent/main.ts:43:14)
    at async file:///tmp/deno-compile-agent/server-monitor-app/agent/main.ts:89:19

[gg-sr]

deno 2.1.4 (stable, release, x86_64-unknown-linux-gnu)
v8 13.0.245.12-rusty
typescript 5.6.2

---

Similarly, writing to /dev/stdout seems to require --allow-all.

$ deno repl --allow-write=/dev/stdout
Deno 2.1.4
exit using ctrl+d, ctrl+c, or close()
> await Deno.writeTextFile('/dev/stdout', 'hello world')
Uncaught NotCapable: Requires all access to "/dev/stdout", run again with the --allow-all flag
    at writeFile (ext:deno_fs/30_fs.js:841:13)
    at Object.writeTextFile (ext:deno_fs/30_fs.js:883:12)
    at <anonymous>:1:33

I'd like to run commands that accept an output file path, and sometimes I want that "output file" to be /dev/stdout, which requires me to pass --allow-all (since --allow-all=/dev/stdout is not allowed).