How to use zbus to list block devices?

Question

I want to list all the available block devices in the system using a dbus implementation called zbus.

The UDisks2 documentation mentions a method call on org.freedesktop.UDisks2.Manager interface called GetBlockDevices which accepts IN a{sv} options, OUT ao block_objects for method parameters.

Using zbus, I write:

use std::error::Error;
use std::result::Result;
use zbus::{Connection, Proxy};

fn main() -> Result<(), Box<dyn Error>> {
    let connection = Connection::new_system()?;
    let p = Proxy::new(
        &connection,
        "org.freedesktop.UDisks2",
        "/org/freedesktop/UDisks2/Manager",
        "org.freedesktop.UDisks2.Manager",
    )?;
    let resp: Vec<zvariant::ObjectPath> = p.call("GetBlockDevices", &std::collections::HashMap::<String, zvariant::Value>::new())?;
    dbg!(resp);
    Ok(())
}

As far as I understand, zvariant Values represent a DBus Variant. However I get the following error:

error: implementation of `serde::de::Deserialize` is not general enough
   --> src/main.rs:13:45
    |
13  |       let resp: Vec<zvariant::ObjectPath> = p.call("GetBlockDevices", &std::collections::HashMap::<String, zvariant::Value>::new())?;
    |                                               ^^^^ implementation of `serde::de::Deserialize` is not general enough
    | 
   ::: /home/adnan338/.cargo/registry/src/github.com-1ecc6299db9ec823/serde-1.0.115/src/de/mod.rs:531:1
    |
531 | / pub trait Deserialize<'de>: Sized {
532 | |     /// Deserialize this value from the given Serde deserializer.
533 | |     ///
534 | |     /// See the [Implementing `Deserialize`][impl-deserialize] section of the
...   |
569 | |     }
570 | | }
    | |_- trait `serde::de::Deserialize` defined here
    |
    = note: `std::vec::Vec<zvariant::object_path::ObjectPath<'_>>` must implement `serde::de::Deserialize<'0>`, for any lifetime `'0`...
    = note: ...but `std::vec::Vec<zvariant::object_path::ObjectPath<'_>>` actually implements `serde::de::Deserialize<'1>`, for some specific lifetime `'1`

What's causing this and how can I avoid this error?

zeenix · Accepted Answer · 2020-09-23 15:12:31Z

3

Firstly, thanks for trying out our crate. The issue is that zbus::Proxy::call expects the return value to be an owned one, while you're deserializing to an unowned type. Both of the the following work:

// OwnedObjectPath require zvariant >= 2.2.0
let resp: Vec<zvariant::OwnedObjectPath> = p.call(
    "GetBlockDevices",
    &std::collections::HashMap::<String, zvariant::Value>::new(),
)?;

let resp = p.call_method(
    "GetBlockDevices",
    &std::collections::HashMap::<String, zvariant::Value>::new(),
)?; 
let resp: Vec<zvariant::ObjectPath> = resp.body()?;

answered Sep 23, 2020 at 15:12

zeenix

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