[PATCH proxmox-backup 3/4] datastore: s3: avoid double calls to rather expensive backup_user()

[Christian Ebner <c.ebner@proxmox.com>]

backup_user() internally calls User::from_name() which itself uses
getpwnam_r(3) [0] and therefore can involve nsswitch.conf and
/etc/passwd parsing, including several syscalls to do so as
demonstrated by a strace in [1].

Therefore, only call the helper once and clone it to get multiple
instances instead.

[0] https://docs.rs/nix/0.29.0/nix/unistd/struct.User.html#method.from_name
[1] https://bugzilla.proxmox.com/show_bug.cgi?id=7642

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-datastore/src/datastore.rs | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index 42aa96464..988cda833 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -492,16 +492,18 @@ impl DataStore {
                     .clone()
                     .ok_or_else(|| format_err!("missing bucket for s3 backend"))?;
 
+                let user = pbs_config::backup_user()?;
+
                 let (config, _config_digest) = pbs_config::s3::config()?;
                 let config: S3ClientConf = config.lookup(S3_CFG_TYPE_ID, s3_client_id)?;
                 let rate_limiter_options = S3RateLimiterOptions {
                     id: s3_client_id.to_string(),
-                    user: pbs_config::backup_user()?,
+                    user: user.clone(),
                     base_path: S3_CLIENT_RATE_LIMITER_BASE_PATH.into(),
                 };
                 let request_counter_config = S3RequestCounterConfig {
                     id: format!("{s3_client_id}-{bucket}-{}", self.name()),
-                    user: pbs_config::backup_user()?,
+                    user: user.clone(),
                     base_path: S3_CLIENT_REQUEST_COUNTER_BASE_PATH.into(),
                 };
 
@@ -3348,6 +3350,8 @@ impl DataStore {
             return Ok((backend_type, None));
         }
 
+        let user = pbs_config::backup_user()?;
+
         let s3_client_id = backend_config
             .client
             .as_ref()
@@ -3363,12 +3367,12 @@ impl DataStore {
             .with_context(|| format!("no '{s3_client_id}' in config"))?;
         let rate_limiter_options = S3RateLimiterOptions {
             id: s3_client_id.to_string(),
-            user: pbs_config::backup_user()?,
+            user: user.clone(),
             base_path: S3_CLIENT_RATE_LIMITER_BASE_PATH.into(),
         };
         let request_counter_config = S3RequestCounterConfig {
             id: format!("{s3_client_id}-{bucket}-{}", datastore_config.name),
-            user: pbs_config::backup_user()?,
+            user: user.clone(),
             base_path: S3_CLIENT_REQUEST_COUNTER_BASE_PATH.into(),
         };
 
-- 
2.47.3