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Log fallback due to lack of resources as info rather than error. #590

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Log fallback due to lack of resources as info rather than error. #590

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78b3798
Log fallback due to lack of resources as info rather than error.
EMachin3 Dec 28, 2024
b9a23b9
small newline linting fix
EMachin3 Dec 28, 2024
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31 changes: 24 additions & 7 deletions vm/devices/storage/disk_nvme/nvme_driver/src/driver.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -98,6 +98,12 @@ pub enum RestoreError {
InvalidData,
}

#[derive(Debug, Error)]
pub enum IOError {
#[error("no more io queues available")]
NoMoreIoQueues,
}

#[derive(Inspect)]
struct IoQueue {
queue: QueuePair,
Expand Down Expand Up @@ -797,12 +803,23 @@ impl<T: DeviceBacking> DriverWorkerTask<T> {
.find_map(|(i, issuer)| issuer.get().map(|issuer| (i, issuer)))
.unwrap();

tracing::error!(
cpu,
fallback_cpu,
error = err.as_ref() as &dyn std::error::Error,
"failed to create io queue, falling back"
);
// Error due to running out of IO queues as a result of
// lack of hardware resources should be logged as INFO
if err.downcast_ref::<IOError>().is_some() {
tracing::info!(
cpu,
fallback_cpu,
error = err.as_ref() as &dyn std::error::Error,
"failed to create io queue, falling back"
);
} else {
tracing::error!(
cpu,
fallback_cpu,
error = err.as_ref() as &dyn std::error::Error,
"failed to create io queue, falling back"
);
}
fallback.clone()
}
};
Expand All @@ -819,7 +836,7 @@ impl<T: DeviceBacking> DriverWorkerTask<T> {
cpu: u32,
) -> anyhow::Result<IoIssuer> {
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I'll leave it up to the storage folks to decide if they want to take this, but I think our preferred approach would be to convert these functions to returning full thiserror enums for all the different cases and then just matching on that, instead of using downcast_ref.

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Agreed - many thanks for the contribution @EMancin3, and for the feedback here, @smalis-msft.

I am in favor of making a code change to reduce the severity of this message. I also agree with Steven's feedback. (Tho, while I'm confident in the storage space, I'm still learning Rust and I'm open to a conversation).

I would suggest we generalize this ... :

#[derive(Debug, Error)]
pub enum DeviceCapabilityError {
    #[error("no more io queues available, max {0}", usize)]
    NoMoreIoQueues,
}

Since anyhow::Result is a shortcut for Result<T, anyhow::Error> and anyhow::Error implements std::error::Error, we should be able to then do:

    async fn create_io_queue(
        &mut self,
        state: &mut WorkerState,
        cpu: u32,
    ) -> Result<IoIssuer, Error> {

...

        if self.io.len() >= state.max_io_queues as usize {
            return Err(DeviceCapabilityError::NoMoreIoQueues(state.max_io_queues))
        }

and then in the calling code match on Error type.

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Agree with @mattkur.

if self.io.len() >= state.max_io_queues as usize {
anyhow::bail!("no more io queues available");
anyhow::bail!(IOError::NoMoreIoQueues);
}

let qid = self.io.len() as u16 + 1;
Expand Down
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