rgw: add radosgw-admin sub-command to set-min-shards for a bucket

There is now a mechansim to set the minimum number of shards when a
bucket is created, and dynamic resharding adheres to that
setting. This adds the ability to modify that minimum shard count that
exists within the bucket layout of the bucket instance
object. Example:

    radosgw-admin bucket set-min-shards --bucket=<bucket> \
        --num-shards=<value>

Signed-off-by: J. Eric Ivancich <[email protected]>

Author: ivancich

src/rgw/radosgw-admin/radosgw-admin.cc

@@ -1,10 +1,9 @@
-
 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
 // vim: ts=8 sw=2 smarttab ft=cpp
 
 /*
  * Copyright (C) 2025 IBM 
-*/
+ */
 
 #include <cerrno>
 #include <string>
@@ -169,6 +168,7 @@ void usage()
   cout << "  bucket check unlinked            check for object versions that are not visible in a bucket listing \n";
   cout << "  bucket chown                     link bucket to specified user and update its object ACLs\n";
   cout << "  bucket reshard                   reshard bucket\n";
+  cout << "  bucket set-min-shards            set the minimum number of shards that dynamic resharding will consider for a bucket\n";
   cout << "  bucket rewrite                   rewrite all objects in the specified bucket\n";
   cout << "  bucket sync checkpoint           poll a bucket's sync status until it catches up to its remote\n";
   cout << "  bucket sync disable              disable bucket sync\n";
@@ -699,6 +699,7 @@ enum class OPT {
   BUCKET_RM,
   BUCKET_REWRITE,
   BUCKET_RESHARD,
+  BUCKET_SET_MIN_SHARDS,
   BUCKET_CHOWN,
   BUCKET_RADOS_LIST,
   BUCKET_SHARD_OBJECTS,
@@ -937,6 +938,7 @@ static SimpleCmd::Commands all_cmds = {
   { "bucket rm", OPT::BUCKET_RM },
   { "bucket rewrite", OPT::BUCKET_REWRITE },
   { "bucket reshard", OPT::BUCKET_RESHARD },
+  { "bucket set-min-shards", OPT::BUCKET_SET_MIN_SHARDS },
   { "bucket chown", OPT::BUCKET_CHOWN },
   { "bucket radoslist", OPT::BUCKET_RADOS_LIST },
   { "bucket rados list", OPT::BUCKET_RADOS_LIST },
@@ -8803,6 +8805,51 @@ int main(int argc, const char **argv)
     }
   } // OPT_RESHARD_CANCEL
 
+  if (opt_cmd == OPT::BUCKET_SET_MIN_SHARDS) {
+    if (bucket_name.empty()) {
+      cerr << "ERROR: bucket not specified" << std::endl;
+      return -EINVAL;
+    }
+
+    if (!num_shards_specified) {
+      cerr << "ERROR: --num-shards not specified" << std::endl;
+      return -EINVAL;
+    }
+
+    if (num_shards < 1) {
+      cerr << "ERROR: --num-shards must be at least 1" << std::endl;
+      return -EINVAL;
+    }
+
+    int ret = init_bucket(tenant, bucket_name, bucket_id, &bucket);
+    if (ret < 0) {
+      return -ret;
+    }
+    auto& bucket_info = bucket->get_info();
+
+    const rgw::BucketIndexType type =
+      bucket_info.layout.current_index.layout.type;
+    if (type != rgw::BucketIndexType::Normal) {
+      cerr << "ERROR: the bucket's layout is type " << type <<
+	" instead of type " << rgw::BucketIndexType::Normal <<
+	" and therefore does not have a "
+	"minimum number of shards that can be altered" << std::endl;
+      return EINVAL;
+    }
+
+    uint32_t& min_num_shards =
+      bucket_info.layout.current_index.layout.normal.min_num_shards;
+    min_num_shards = num_shards;
+
+    ret = bucket->put_info(dpp(), false, real_time(), null_yield);
+    if (ret < 0) {
+      cerr << "ERROR: failed writing bucket instance info: " << cpp_strerror(-ret) << std::endl;
+      return -ret;
+    }
+
+    return 0;
+  } // SET_MIN_SHARDS
+
   if (opt_cmd == OPT::OBJECT_UNLINK) {
     int ret = init_bucket(tenant, bucket_name, bucket_id, &bucket);
     if (ret < 0) {

src/rgw/rgw_sal.h

@@ -686,7 +686,7 @@ class Driver {
 
     /** Register admin APIs unique to this driver */
     virtual void register_admin_apis(RGWRESTMgr* mgr) = 0;
-};
+}; // class Driver
 
 
 /// \brief Ref-counted callback object for User/Bucket read_stats_async().

src/test/cli/radosgw-admin/help.t

@@ -38,6 +38,7 @@
     bucket check unlinked            check for object versions that are not visible in a bucket listing 
     bucket chown                     link bucket to specified user and update its object ACLs
     bucket reshard                   reshard bucket
+    bucket set-min-shards            set the minimum number of shards that dynamic resharding will consider for a bucket
     bucket rewrite                   rewrite all objects in the specified bucket
     bucket sync checkpoint           poll a bucket's sync status until it catches up to its remote
     bucket sync disable              disable bucket sync