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Add function to enumerate devices #208

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Add function to enumerate devices #208

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6a740e3
Add function to enumerate devices
jlHertel Oct 27, 2024
9bc03d2
Update src/node/mod.rs
jlHertel Oct 28, 2024
629028c
Update src/node/mod.rs
jlHertel Oct 28, 2024
7d9cf3d
Remove unneeded type hint
jlHertel Oct 28, 2024
6c18b86
Simplify entry check
jlHertel Oct 28, 2024
737b01d
Update code to address review comments
jlHertel Oct 28, 2024
73e2c2a
Remove unnecessary into_iter call
jlHertel Oct 28, 2024
d7684be
Format code
jlHertel Oct 28, 2024
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2 changes: 1 addition & 1 deletion drm-ffi/drm-sys/src/bindings.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
/* automatically generated by rust-bindgen 0.69.4 */
/* automatically generated by rust-bindgen 0.69.5 */

pub const DRM_NAME: &[u8; 4] = b"drm\0";
pub const DRM_MIN_ORDER: u32 = 5;
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7 changes: 7 additions & 0 deletions examples/enumerate.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
use drm::node;

pub fn main() {
let devices = node::drm_get_devices();

println!("{:?}", devices.unwrap());
}
20 changes: 19 additions & 1 deletion src/node/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ pub mod constants;

use std::error::Error;
use std::fmt::{self, Debug, Display, Formatter};
use std::io;
use std::{fs, io};
use std::os::unix::io::AsFd;
use std::path::{Path, PathBuf};

Expand Down Expand Up @@ -380,3 +380,21 @@ pub fn dev_path(dev: dev_t, ty: NodeType) -> io::Result<PathBuf> {
),
))
}

/// Returns a Vector with all DRM Nodes we managed to find. There might be duplicates.
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pub fn drm_get_devices() -> Result<Vec<DrmNode>, io::Error> {
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Could this instead return impl Iterator<Item = io::Result<DrmNode>>?

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I'm not sure what would be the best approach here.
We can have IO Errors only by failing to open/read the /dev directory.
For the devices themselves, we will only get errors if they aren't DRM devices, which should be the case for the majority of stuff in /dev.

Would iterator improve anything in regards to the error handling?

Also, sorry if my answers are a bit confusing. I'm quite new to Rust, so I might be missing the big-picture on how to better handle errors/iterators.

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@MarijnS95 MarijnS95 Oct 28, 2024 •
edited
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We can have IO Errors only by failing to open/read the /dev directory.

That could be handled with:

io::Result<impl Iterator<Item = io::Result<DrmNode>>>

For the devices themselves, we will only get errors if they aren't DRM devices, which should be the case for the majority of stuff in /dev.

And as just mentioned below, drmGetDevices2() skips errors while opening sub-devices, so we might as well return an iterator over DrmNode directly:

io::Result<impl Iterator<Item = DrmNode>>

For the devices themselves, we will only get errors if they aren't DRM devices, which should be the case for the majority of stuff in /dev.

And as below, on most platforms except FreeBSD we should be reading /dev/dri.

Also, sorry if my answers are a bit confusing. I'm quite new to Rust, so I might be missing the big-picture on how to better handle errors/iterators.

No worries, I think everyone is happy to educate new contributors on Rust as well as describing the "Rust style" used in drm-rs (as much as we're still discovering what that's supposed to be).

Regarding the drm_get_devices() function name (based on drmGetDevices(2)()), I'd drop the drm_ prefix since we're already in the drm crate (i.e. a fully qualified call would look like drm::node::drm_get_devices() which is somewhat superfluous) and then also drop the get_ prefix because of the no get_ prefix convention.

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Thanks for all the feedback, it's highly appreciated.
I pushed the changes with everything you suggested. Do you mind to give another look?

let mut devices: Vec<DrmNode> = vec![];
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fs::read_dir("/dev")?
.for_each(|entry| {
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How about making this a .map().collect() rather than a side-effecting for_each()? If that, use regular control flow with for entry in fs::read_dir(..)? { .. }.

The .collect() can be dropped if using @notgull's suggestion to return an iterator instead.

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Wouldn't we need to filter the results in some way if we use .map()? Asking as we check all devices and likely a lot of them aren't DRM devices, so we need to skip them. This validation is done right now by calling DrmNode::from_path().

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Such filtering can be implemented by a .filter_map(), but I'm hesitant to stat() every device on the system to see if it is a DRM device.

Since drmGetDevices2() was requested, I expected this feature to be built after that function. While it does also appear to ignore any error from processing individual devices, this function does open DRM_DIR_NAME which is /dev/dri on every platform except FreeBSD where it is /dev. This way we don't have to stat() devices that we know won't be DRM devices in the first place.

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Hey thanks for the pointers. I somehow completely missed the fact that DRM_DIR_NAME was different in certain platforms. I will update the code to also use /dev/dri for all platforms except FreeBSD.

if entry.is_ok() {
let device_path = entry.unwrap().path();
let node = DrmNode::from_path(device_path);
if node.is_ok() {
devices.push(node.unwrap())
}
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}
});

Ok(devices)
}