mon: add new configuration to limit filesystem xattrs size

This new configuration option will allow to define the maximum size for a
filesystem xattrs blob.  This is a filesystem-wide knob that will replace
the per-MDS mds_max_xattr_pairs_size option.

Note:

The kernel client patch to handle this new configuration was merged before
the corresponding ceph-side pull-request.  This was unfortunate because in
the meantime PR ceph#43284 was merged and the encoding/decoding of
'bal_rank_mask' got in between.  Hence the 'max_xattr_size' is being
encoding/decoded before 'bal_rank_mask'.

URL: https://tracker.ceph.com/issues/55725
Signed-off-by: Luís Henriques <lhenriques@suse.de>

src/mds/MDSMap.cc

@@ -177,6 +177,7 @@ void MDSMap::dump(Formatter *f) const
   cephfs_dump_features(f, required_client_features);
   f->close_section();
   f->dump_int("max_file_size", max_file_size);
+  f->dump_int("max_xattr_size", max_xattr_size);
   f->dump_int("last_failure", last_failure);
   f->dump_int("last_failure_osd_epoch", last_failure_osd_epoch);
   f->open_object_section("compat");
@@ -268,6 +269,7 @@ void MDSMap::print(ostream& out) const
   out << "session_timeout\t" << session_timeout << "\n"
       << "session_autoclose\t" << session_autoclose << "\n";
   out << "max_file_size\t" << max_file_size << "\n";
+  out << "max_xattr_size\t" << max_xattr_size << "\n";
   out << "required_client_features\t" << cephfs_stringify_features(required_client_features) << "\n";
   out << "last_failure\t" << last_failure << "\n"
       << "last_failure_osd_epoch\t" << last_failure_osd_epoch << "\n";
@@ -790,6 +792,7 @@ void MDSMap::encode(bufferlist& bl, uint64_t features) const
     encode(min_compat_client, bl);
   }
   encode(required_client_features, bl);
+  encode(max_xattr_size, bl);
   encode(bal_rank_mask, bl);
   ENCODE_FINISH(bl);
 }
@@ -939,6 +942,7 @@ void MDSMap::decode(bufferlist::const_iterator& p)
   }
 
   if (ev >= 17) {
+    decode(max_xattr_size, p);
     decode(bal_rank_mask, p);
   }
 

src/mds/MDSMap.h

@@ -50,6 +50,12 @@ static inline const auto MDS_FEATURE_INCOMPAT_SNAPREALM_V2 = CompatSet::Feature(
 
 #define MDS_FS_NAME_DEFAULT "cephfs"
 
+/*
+ * Maximum size of xattrs the MDS can handle per inode by default.  This
+ * includes the attribute name and 4+4 bytes for the key/value sizes.
+ */
+#define MDS_MAX_XATTR_SIZE (1<<16) /* 64K */
+
 class health_check_map_t;
 
 class MDSMap {
@@ -196,6 +202,9 @@ class MDSMap {
   uint64_t get_max_filesize() const { return max_file_size; }
   void set_max_filesize(uint64_t m) { max_file_size = m; }
 
+  uint64_t get_max_xattr_size() const { return max_xattr_size; }
+  void set_max_xattr_size(uint64_t m) { max_xattr_size = m; }
+
   void set_min_compat_client(ceph_release_t version);
 
   void add_required_client_feature(size_t bit) {
@@ -620,6 +629,8 @@ class MDSMap {
   __u32 session_autoclose = 300;
   uint64_t max_file_size = 1ULL<<40; /* 1TB */
 
+  uint64_t max_xattr_size = MDS_MAX_XATTR_SIZE;
+
   feature_bitset_t required_client_features;
 
   std::vector<int64_t> data_pools;  // file data pools available to clients (via an ioctl).  first is the default.

src/mon/FSCommands.cc

@@ -461,6 +461,17 @@ class SetHandler : public FileSystemCommandHandler
       {
         fs->mds_map.set_max_filesize(n);
       });
+    } else if (var == "max_xattr_size") {
+      if (interr.length()) {
+	ss << var << " requires an integer value";
+	return -EINVAL;
+      }
+      fsmap.modify_filesystem(
+          fs->fscid,
+          [n](std::shared_ptr<Filesystem> fs)
+      {
+        fs->mds_map.set_max_xattr_size(n);
+      });
     } else if (var == "allow_new_snaps") {
       bool enable_snaps = false;
       int r = parse_bool(val, &enable_snaps, ss);

src/mon/MonCommands.h

@@ -378,7 +378,7 @@ COMMAND("fs set "
         "|allow_new_snaps|inline_data|cluster_down|allow_dirfrags|balancer"
         "|standby_count_wanted|session_timeout|session_autoclose"
         "|allow_standby_replay|down|joinable|min_compat_client|bal_rank_mask"
-	"|refuse_client_session "
+	"|refuse_client_session|max_xattr_size "
 	"name=val,type=CephString "
 	"name=yes_i_really_mean_it,type=CephBool,req=false "
 	"name=yes_i_really_really_mean_it,type=CephBool,req=false",