all: Support syncing extended attributes (fixes #2698) (#8513)

This adds support for syncing extended attributes on supported
filesystem on Linux, macOS, FreeBSD and NetBSD. Windows is currently
excluded because the APIs seem onerous and annoying and frankly the uses
cases seem few and far between. On Unixes this also covers ACLs as those
are stored as extended attributes.

Similar to ownership syncing this will optional & opt-in, which two
settings controlling the main behavior: one to "sync" xattrs (read &
write) and another one to "scan" xattrs (only read them so other devices
can "sync" them, but not apply any locally).

Co-authored-by: Tomasz Wilczyński <twilczynski@naver.com>

proto/lib/config/folderconfiguration.proto

@@ -55,10 +55,31 @@ message FolderConfiguration {
     bool                               case_sensitive_fs          = 33 [(ext.goname) = "CaseSensitiveFS", (ext.xml) = "caseSensitiveFS", (ext.json) = "caseSensitiveFS"];
     bool                               follow_junctions           = 34 [(ext.goname) = "JunctionsAsDirs", (ext.xml) = "junctionsAsDirs", (ext.json) = "junctionsAsDirs"];
     bool                               sync_ownership             = 35;
-    bool                               scan_ownership             = 36;
+    bool                               send_ownership             = 36;
+    bool                               sync_xattrs                = 37;
+    bool                               send_xattrs                = 38;
+    XattrFilter                        xattr_filter               = 39;
 
     // Legacy deprecated
     bool   read_only         = 9000 [deprecated=true, (ext.xml) = "ro,attr,omitempty"];
     double min_disk_free_pct = 9001 [deprecated=true];
     int32  pullers           = 9002 [deprecated=true];
+    bool   scan_ownership    = 9003 [deprecated=true];
+}
+
+// Extended attribute filter. This is a list of patterns to match (glob
+// style), each with an action (permit or deny). First match is used. If the
+// filter is empty, all strings are permitted. If the filter is non-empty,
+// the default action becomes deny. To counter this, you can use the "*"
+// pattern to match all strings at the end of the filter. There are also
+// limits on the size of accepted attributes.
+message XattrFilter {
+    repeated XattrFilterEntry entries               = 1 [(ext.xml) = "entry"];
+    int32                     max_single_entry_size = 2 [(ext.xml) = "maxSingleEntrySize", (ext.default) = "1024"];
+    int32                     max_total_size        = 3 [(ext.xml) = "maxTotalSize", (ext.default) = "4096"];
+}
+
+message XattrFilterEntry {
+    string match  = 1 [(ext.xml) = "match,attr"];
+    bool   permit = 2 [(ext.xml) = "permit,attr"];
 }

proto/lib/db/structs.proto

@@ -39,8 +39,9 @@ message FileInfoTruncated {
     protocol.PlatformData platform       = 14;
 
     // see bep.proto
-    uint32 local_flags  = 1000;
-    bytes  version_hash = 1001;
+    uint32 local_flags     = 1000;
+    bytes  version_hash    = 1001;
+    int64  inode_change_ns = 1002;
 
     bool deleted        = 6;
     bool invalid        = 7 [(ext.goname) = "RawInvalid"];

proto/lib/protocol/bep.proto

@@ -114,10 +114,15 @@ message FileInfo {
     // received (we make sure to zero it), nonetheless we need it on our
     // struct and to be able to serialize it to/from the database.
     uint32 local_flags = 1000;
+
     // The version_hash is an implementation detail and not part of the wire
     // format.
     bytes version_hash = 1001;
 
+    // The time when the inode was last changed (i.e., permissions, xattrs
+    // etc changed). This is host-local, not sent over the wire.
+    int64 inode_change_ns = 1002;
+
     bool deleted        = 6;
     bool invalid        = 7 [(ext.goname) = "RawInvalid"];
     bool no_permissions = 8;
@@ -151,6 +156,10 @@ message Counter {
 message PlatformData {
     UnixData    unix    = 1 [(gogoproto.nullable) = true];
     WindowsData windows = 2 [(gogoproto.nullable) = true];
+    XattrData   linux   = 3 [(gogoproto.nullable) = true];
+    XattrData   darwin  = 4 [(gogoproto.nullable) = true];
+    XattrData   freebsd = 5 [(gogoproto.nullable) = true, (ext.goname) = "FreeBSD"];
+    XattrData   netbsd  = 6 [(gogoproto.nullable) = true, (ext.goname) = "NetBSD"];
 }
 
 message UnixData {
@@ -171,6 +180,15 @@ message WindowsData {
     bool   owner_is_group = 2;
 }
 
+message XattrData {
+    repeated Xattr xattrs = 1;
+}
+
+message Xattr {
+    string name  = 1;
+    bytes  value = 2;
+}
+
 // Request
 
 message Request {