[pbs-devel] [RFC PATCH proxmox-backup 1/2] pbs-config: use trait object for the backup lock guard

[Dominik Csapak]

On 9/6/21 12:25, Wolfgang Bumiller wrote:
> On Fri, Sep 03, 2021 at 09:17:51AM +0200, Dominik Csapak wrote:
>> instead of a fixed type. The old implementation is now
>> BackupLockGuardImpl and implements the trait.
>>
>> At the same time, introduce a type alias with the same name as the
>> previous struct, so that the users of it do not have to change anything.
>>
>> This makes it possible for us to have a different lock implementation
>> for e.g. tests (where we do not actually want to lock)
>>
>> Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
>> ---
>>   pbs-config/src/lib.rs | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/pbs-config/src/lib.rs b/pbs-config/src/lib.rs
>> index 9d8c730d..604fe9d7 100644
>> --- a/pbs-config/src/lib.rs
>> +++ b/pbs-config/src/lib.rs
>> @@ -16,7 +16,14 @@ pub fn backup_group() -> Result<nix::unistd::Group, Error> {
>>       pbs_tools::sys::query_group(BACKUP_GROUP_NAME)?
>>           .ok_or_else(|| format_err!("Unable to lookup '{}' group.", BACKUP_GROUP_NAME))
>>   }
>> -pub struct BackupLockGuard(std::fs::File);
>> +
>> +pub trait BackupLockGuardTrait: Send + Sync + Unpin + std::panic::UnwindSafe + std::panic::RefUnwindSafe { }
>> +
>> +struct BackupLockGuardImpl(std::fs::File);
>> +
>> +impl BackupLockGuardTrait for BackupLockGuardImpl {}
>> +
>> +pub type BackupLockGuard = Box<dyn BackupLockGuardTrait>;
> 
> Since the File is abstracted away in a custom type, 2 more possibilities
> come to mind:
> 
>      pub struct BackupLockGuard(Option<File>);
> 
> and cfg(test) would just use `None`
> 
> or turn the File into our `Fd` type from the proxmox crate and use
> `Fd::from_raw_fd(-1)` when no lock is used
> 
> That way we don't even need the trait
> 

sound ok in general, but then we have to make the field public no ?
and then we could also open a bug file too, no change in the type needed 
at all... but i thought we want to avoid making the underlying field 
public...