fix gathering io stats for zpools

if a datastore or root is not used directly on the pool dir
(e.g. the installer creates 2 sub datasets ROOT/pbs-1), info in
/proc/self/mountinfo returns not the pool, but the path to the
dataset, which has no iostats itself in /proc/spl/kstat/zfs/
but only the pool itself

so instead of not gathering data at all, gather the info from the
underlying pool instead. if one has multiple datastores on the same
pool those rrd stats will be the same for all those datastores now
(instead of empty) similar to 'normal' directories

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/bin/proxmox-backup-proxy.rs

@@ -41,6 +41,7 @@ use proxmox_backup::tools::{
     disks::{
         DiskManage,
         zfs_pool_stats,
+        get_pool_from_dataset,
     },
     logrotate::LogRotate,
     socket::{
@@ -865,8 +866,9 @@ fn gather_disk_stats(disk_manager: Arc<DiskManage>, path: &Path, rrd_prefix: &st
             let mut device_stat = None;
             match fs_type.as_str() {
                 "zfs" => {
-                    if let Some(pool) = source {
-                        match zfs_pool_stats(&pool) {
+                    if let Some(source) = source {
+                        let pool = get_pool_from_dataset(&source).unwrap_or(&source);
+                        match zfs_pool_stats(pool) {
                             Ok(stat) => device_stat = stat,
                             Err(err) => eprintln!("zfs_pool_stats({:?}) failed - {}", pool, err),
                         }

src/tools/disks/zfs.rs

@@ -16,6 +16,17 @@ lazy_static!{
     };
 }
 
+/// returns pool from dataset path of the form 'rpool/ROOT/pbs-1'
+pub fn get_pool_from_dataset(dataset: &OsStr) -> Option<&OsStr> {
+    if let Some(dataset) = dataset.to_str() {
+        if let Some(idx) = dataset.find('/') {
+            return Some(&dataset[0..idx].as_ref());
+        }
+    }
+
+    None
+}
+
 /// Returns kernel IO-stats for zfs pools
 pub fn zfs_pool_stats(pool: &OsStr) -> Result<Option<BlockDevStat>, Error> {