Re: [pve-devel] [PATCH pve-esxi-import-tools 1/1] improve error handling before mounting

[Dominik Csapak <d.csapak@proxmox.com>]

On 5/8/24 16:26, Thomas Lamprecht wrote:
> On 08/05/2024 14:41, Dominik Csapak wrote:
>> when we fail early in the mount process, we did not log any error to the
>> syslog, but only the top most one to stderr.
>>
>> sadly we were not able to see them anywhere, so improve the log by
>> * log the complete error chain with log::error (so we also can see the
>>    causes)
>> * add more context hints in main_do
>>
>> This can help debug issues where we failed early and could not see any
>> error output otherwise, e.g. this thread in the forum:
>>
>> https://forum.proxmox.com/threads/146248/
>>
>> Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
>> ---
>>   src/main.rs | 36 +++++++++++++++++++++++++++---------
>>   1 file changed, 27 insertions(+), 9 deletions(-)
>>
>> diff --git a/src/main.rs b/src/main.rs
>> index 281ec3d..a8b2bb6 100644
>> --- a/src/main.rs
>> +++ b/src/main.rs
>> @@ -1,4 +1,5 @@
>>   use std::ffi::{CString, OsStr, OsString};
>> +use std::fmt::Write;
>>   use std::io;
>>   use std::os::fd::RawFd;
>>   use std::os::unix::ffi::OsStrExt;
>> @@ -221,7 +222,12 @@ fn main() {
>>       });
>>   
>>       if let Err(err) = runtime.block_on(main_do()) {
>> -        eprintln!("Error: {}", err);
>> +        let mut err_chain = String::new();
>> +        for err in err.chain() {
>> +            let _ = writeln!(err_chain, " {err}");
> 
> is the extra whitespace intended? At least the first line would then have two
> consecutive whitespaces, one from here and one from the prefix below on log and
> println.

yes that was intentionally, but the whitespace in log was not
i wanted to print something like:

Error: <error1>
  <error2>
  <error3>
etc.

we could ofc print them all in one line too... but not a big fan of that
for readability

> 
>> +        }
>> +        println!("Error: {err}");
>> +        log::error!("Error: {err_chain}");
>>           std::process::exit(-1);
>>       }
>>   }
>> @@ -236,15 +242,15 @@ async fn main_do() -> Result<(), Error> {
>>               usage(&arg0, std::io::stderr(), 1);
>>           }
>>       };
>> -    parse_manifest(&args.manifest)?;
>> +    parse_manifest(&args.manifest).context("failed to parse manifest")?;
>>   
>>       let change_uid = match args.change_user.as_deref() {
>> -        Some(user) => Some(get_uid(user)?),
>> +        Some(user) => Some(get_uid(user).context("failed to get uid")?),
>>           None => None,
>>       };
>>   
>>       let change_gid = match args.change_group.as_deref() {
>> -        Some(group) => Some(get_gid(group)?),
>> +        Some(group) => Some(get_gid(group).context("failed to get gid")?),
>>           None => None,
>>       };
>>   
>> @@ -255,10 +261,12 @@ async fn main_do() -> Result<(), Error> {
>>           .enable_readdirplus();
>>   
>>       for opt in args.mount_options {
>> -        fuse = fuse.options_os(&opt)?;
>> +        fuse = fuse
>> +            .options_os(&opt)
>> +            .context("failed to get fuse options")?;
>>       }
>>   
>> -    unmount_if_mounted(&args.mount_path)?;
>> +    unmount_if_mounted(&args.mount_path).context("failed to unmount")?;
>>   
>>       let mut fuse = fuse
>>           .build()
>> @@ -302,9 +310,19 @@ async fn main_do() -> Result<(), Error> {
>>               let fs_datastore = fs_datacenter.create_datastore(datastore);
>>   
>>               log::debug!("loading {datacenter:?}/{datastore:?}/{path:?}");
>> -            let config =
>> -                vmx::VmConfig::parse(client.open_file(datacenter, datastore, path).await?, path)
>> -                    .await?;
>> +            let config = vmx::VmConfig::parse(
>> +                client
>> +                    .open_file(datacenter, datastore, path)
>> +                    .await
>> +                    .with_context(|| {
>> +                        format!("error opening file for: {datacenter} {datastore} {path}")
> 
> should that context be added unconditionally in open_file?

how do you mean? there is only one function in open_file that can fail, so do you mean there?

AFAIU with_context/context is only implemented on Result/Option and there is no way to 'add it' to a
function for all `foo()?` calls automatically? (or maybe I'm misunderstanding something here?)

> 
> Also drop the `for: `, rather something like "error when opening file '{...}'"
> 
> And FWIW, in above debug log the variable triple is printed as path,
> and it's also accessible that way on FS level, so might make sense to
> keep it that way.

yep, I'll use the same format

> 
>> +                    })?,
> 
> can we move this to a separate `let config =` line before calling parse on is,
> this gets rather convoluted and with rust one can nicely override the same
> variable in an explicit way, so this here IMO better expressed that way.

sure

> 
>> +                path,
>> +            )
>> +            .await
>> +            .with_context(|| {
>> +                format!("failed to parse vm config for {datacenter} {datastore} {path}")
>> +            })?;
> 
> Similar here, isn't adding that context belonging in the parse fn itself? Might
> hold true for the static context too, as long as the context does not include
> call-site specific info, but only fn implementation-site one, they might be better
> added at the site of implementation to avoid potential repetition.

here we don't have that path in parse anymore (only the underlying fs path that we probably
don't want to log here)

> 
> also s/vm/VM/
> 
>>               log::debug!("{config:#?}");
>>               for disk in config.disks.values() {
>>                   let other_fs_datastore;
> 



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