node: Announce capacity via the attributes

It is done automatically (as a sum of existing space on every file system
available on the configured shards) but can be overwritten if `Capacity`
attribute is provided via the application configuration.
Closes #602.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

CHANGELOG.md

@@ -11,6 +11,7 @@ Changelog for NeoFS Node
 - Stored payload metric per shard (#2023)
 - Histogram metrics for RPC and engine operations (#2351) 
 - SN's version is announced via the attributes automatically but can be overwritten explicitly (#2455)
+- SN's capacity is announced via the attributes automatically but can be overwritten explicitly (#602)
 
 ### Fixed
 - `neo-go` RPC connection loss handling (#1337)

cmd/neofs-node/config.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"sync"
 	atomicstd "sync/atomic"
@@ -532,16 +533,17 @@ var persistateSideChainLastBlockKey = []byte("side_chain_last_processed_block")
 func initCfg(appCfg *config.Config) *cfg {
 	c := &cfg{}
 
-	// attaching version to the node's attributes; do not
-	// move it anywhere below reading the other attributes
-	// since a user should be able to overwrite it.
-	writeAppVersion(c)
-
 	err := c.readConfig(appCfg)
 	if err != nil {
 		panic(fmt.Errorf("config reading: %w", err))
 	}
 
+	// filling system attributes; do not move it anywhere
+	// below applying the other attributes since a user
+	// should be able to overwrite it.
+	err = writeSystemAttributes(c)
+	fatalOnErr(err)
+
 	key := nodeconfig.Key(appCfg)
 
 	var netAddr network.AddressGroup
@@ -969,8 +971,45 @@ func (c *cfg) configWatcher(ctx context.Context) {
 	}
 }
 
-// writeAppVersion writes app version as defined at compilation
-// step to the node's attributes.
-func writeAppVersion(c *cfg) {
+// writeSystemAttributes writes app version as defined at compilation
+// step to the node's attributes and an aggregated disk capacity
+// according to the all space on the all configured disks.
+func writeSystemAttributes(c *cfg) error {
+	// `Version` attribute
+
 	c.cfgNodeInfo.localInfo.SetAttribute("Version", misc.Version)
+
+	// `Capacity` attribute
+
+	var stat syscall.Statfs_t
+	var total uint64 // bytes
+	fsIDMap := make(map[syscall.Fsid]struct{})
+
+	for _, sh := range c.applicationConfiguration.EngineCfg.shards {
+		for _, storage := range sh.subStorages {
+			path := storage.path
+
+			err := util.MkdirAllX(path, storage.perm)
+			if err != nil {
+				return fmt.Errorf("can not create (ensure it exists) dir by '%s' path: %w", path, err)
+			}
+
+			err = syscall.Statfs(path, &stat)
+			if err != nil {
+				return fmt.Errorf("get FS stat by '%s' path: %w", path, err)
+			}
+
+			if _, handled := fsIDMap[stat.Fsid]; handled {
+				continue
+			}
+
+			total += stat.Blocks * uint64(stat.Bsize)
+			fsIDMap[stat.Fsid] = struct{}{}
+		}
+	}
+
+	// according to API description, in GB, not GiB
+	c.cfgNodeInfo.localInfo.SetAttribute("Capacity", strconv.FormatUint(total/(1000*1000*1000), 10))
+
+	return nil
 }