[pbs-devel] [RFC proxmox 2/2] pbs-api-types: extend datastore config by backend config enum

[Christian Ebner]

Allows to configure a backend config variant for a datastore on
creation. The current default `Filesystem` backend variant is
introduced to be compatible with existing storages. A new S3 backend
variant allows to create datastores backed by an S3 compatible object
store instead.

For S3 backends, the id of the corresponding S3 client configuration
is storered. A valid datastore backend configuration for S3 therefore
contains:
```
    ...
    backend s3=<S3_CONFIG_ID>
    ...
```

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
 pbs-api-types/src/datastore.rs | 58 +++++++++++++++++++++++++++++++++-
 1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/pbs-api-types/src/datastore.rs b/pbs-api-types/src/datastore.rs
index 5bd953ac..2b983cb2 100644
--- a/pbs-api-types/src/datastore.rs
+++ b/pbs-api-types/src/datastore.rs
@@ -336,7 +336,11 @@ pub const DATASTORE_TUNING_STRING_SCHEMA: Schema = StringSchema::new("Datastore
             optional: true,
             format: &proxmox_schema::api_types::UUID_FORMAT,
             type: String,
-        }
+        },
+        backend: {
+            schema: DATASTORE_BACKEND_SCHEMA,
+            optional: true,
+        },
     }
 )]
 #[derive(Serialize, Deserialize, Updater, Clone, PartialEq)]
@@ -389,8 +393,59 @@ pub struct DataStoreConfig {
     #[updater(skip)]
     #[serde(skip_serializing_if = "Option::is_none")]
     pub backing_device: Option<String>,
+
+    /// Backend to be used by datastore
+    #[updater(skip)]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub backend: Option<String>,
+}
+
+pub const DATASTORE_BACKEND_SCHEMA: Schema = StringSchema::new("Backend config to be used for datastore.")
+    .format(&ApiStringFormat::VerifyFn(verify_datastore_backend))
+    .type_text("<filesystem|s3=S3_CONFIG_ID>")
+    .schema();
+
+fn verify_datastore_backend(input: &str) -> Result<(), Error> {
+    DatastoreBackendConfig::from_str(input).map(|_| ())
+}
+
+#[derive(Clone, Default)]
+/// Available backend configurations for datastores.
+pub enum DatastoreBackendConfig {
+    #[default]
+    Filesystem,
+    S3(String),
 }
 
+impl std::str::FromStr for DatastoreBackendConfig {
+    type Err = Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if s == "filesystem" {
+            return Ok(Self::Filesystem);
+        }
+        match s.split_once('=') {
+            Some(("s3", value)) => {
+                let s3_config_id = value.parse()?;
+                Ok(Self::S3(s3_config_id))
+            }
+            _ => bail!("invalid datastore backend configuration"),
+        }
+    }
+}
+
+impl std::fmt::Display for DatastoreBackendConfig {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Filesystem => write!(f, "filesystem"),
+            Self::S3(s3_config_id) => write!(f, "s3:{s3_config_id}"),
+        }
+    }
+}
+
+proxmox_serde::forward_serialize_to_display!(DatastoreBackendConfig);
+proxmox_serde::forward_deserialize_to_from_str!(DatastoreBackendConfig);
+
 #[api]
 #[derive(Serialize, Deserialize, Updater, Clone, PartialEq, Default)]
 #[serde(rename_all = "kebab-case")]
@@ -424,6 +479,7 @@ impl DataStoreConfig {
             tuning: None,
             maintenance_mode: None,
             backing_device: None,
+            backend: None,
         }
     }
 
-- 
2.39.5