From 886dac6fcb00b829a5a4dd2c133f7b7709abdf3d Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Mon, 16 Mar 2026 21:23:12 -0700
Subject: [PATCH] Add per-shard EC mount/unmount, location predicate search,
 idx directory for EC

---
 seaweed-volume/src/storage/disk_location.rs |  3 +-
 seaweed-volume/src/storage/store.rs         | 53 ++++++++++++++++++++-
 2 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/seaweed-volume/src/storage/disk_location.rs b/seaweed-volume/src/storage/disk_location.rs
index e8d84b961..70ff6538e 100644
--- a/seaweed-volume/src/storage/disk_location.rs
+++ b/seaweed-volume/src/storage/disk_location.rs
@@ -546,10 +546,11 @@ impl DiskLocation {
         shard_ids: &[u32],
     ) -> Result<(), VolumeError> {
         let dir = self.directory.clone();
+        let idx_dir = self.idx_directory.clone();
         let ec_vol = self
             .ec_volumes
             .entry(vid)
-            .or_insert_with(|| EcVolume::new(&dir, &dir, collection, vid).unwrap());
+            .or_insert_with(|| EcVolume::new(&dir, &idx_dir, collection, vid).unwrap());
 
         for &shard_id in shard_ids {
             let shard = EcVolumeShard::new(&dir, collection, vid, shard_id as u8);
diff --git a/seaweed-volume/src/storage/store.rs b/seaweed-volume/src/storage/store.rs
index 47b65c747..76f69cd99 100644
--- a/seaweed-volume/src/storage/store.rs
+++ b/seaweed-volume/src/storage/store.rs
@@ -147,6 +147,20 @@ impl Store {
         best.map(|(i, _)| i)
     }
 
+    /// Find a free location matching a predicate.
+    /// Matches Go's Store.FindFreeLocation: finds first location passing the filter.
+    pub fn find_free_location_predicate<F>(&self, pred: F) -> Option<usize>
+    where
+        F: Fn(&DiskLocation) -> bool,
+    {
+        for (i, loc) in self.locations.iter().enumerate() {
+            if pred(loc) {
+                return Some(i);
+            }
+        }
+        None
+    }
+
     /// Create a new volume, placing it on the location with the most free space.
     pub fn add_volume(
         &mut self,
@@ -467,7 +481,7 @@ impl Store {
 
     // ---- EC volume operations ----
 
-    /// Mount EC shards for a volume.
+    /// Mount EC shards for a volume (batch).
     pub fn mount_ec_shards(
         &mut self,
         vid: VolumeId,
@@ -485,7 +499,29 @@ impl Store {
         self.locations[loc_idx].mount_ec_shards(vid, collection, shard_ids)
     }
 
-    /// Unmount EC shards for a volume.
+    /// Mount a single EC shard, searching all locations for the shard file.
+    /// Matches Go's Store.MountEcShards which mounts one shard at a time.
+    pub fn mount_ec_shard(
+        &mut self,
+        vid: VolumeId,
+        collection: &str,
+        shard_id: u32,
+    ) -> Result<(), VolumeError> {
+        for loc in &mut self.locations {
+            // Check if the shard file exists on this location
+            let shard = EcVolumeShard::new(&loc.directory, collection, vid, shard_id as u8);
+            if std::path::Path::new(&shard.file_name()).exists() {
+                loc.mount_ec_shards(vid, collection, &[shard_id])?;
+                return Ok(());
+            }
+        }
+        Err(VolumeError::Io(io::Error::new(
+            io::ErrorKind::NotFound,
+            format!("MountEcShards {}.{} not found on disk", vid, shard_id),
+        )))
+    }
+
+    /// Unmount EC shards for a volume (batch).
     pub fn unmount_ec_shards(&mut self, vid: VolumeId, shard_ids: &[u32]) {
         for loc in &mut self.locations {
             if loc.has_ec_volume(vid) {
@@ -495,6 +531,19 @@ impl Store {
         }
     }
 
+    /// Unmount a single EC shard, searching all locations.
+    /// Matches Go's Store.UnmountEcShards which unmounts one shard at a time.
+    pub fn unmount_ec_shard(&mut self, vid: VolumeId, shard_id: u32) -> Result<(), VolumeError> {
+        for loc in &mut self.locations {
+            if loc.has_ec_volume(vid) {
+                loc.unmount_ec_shards(vid, &[shard_id]);
+                return Ok(());
+            }
+        }
+        // Go returns nil if shard not found (no error)
+        Ok(())
+    }
+
     /// Find an EC volume across all locations.
     pub fn find_ec_volume(&self, vid: VolumeId) -> Option<&EcVolume> {
         for loc in &self.locations {