Why syncXattrs is not enabled by default?

Is there a reason for not backing up extended attributes by default when syncing two xattr-compatible directories?

Xattrs can have unbounded amounts of data attached to them, also could be used by acls etc, which could render the files unusable on the other end once synced.

There is also a performance penalty negatively affecting scan time when the option is enabled (see https://docs.syncthing.net/advanced/folder-send-xattrs).

On what system is this? I thought Linux limits Xattrs to the size of a filesystem block (~4KiB).

Windows, Solaris, macOS, you name it. But the main point is what Tomasz says. Why are we arguing about the defaults?

Depends on the version of the Linux kernel. For a given key/value pair, just the value alone can be up to 64 KiB.

And if I recall correctly, storing extended attributes in a separate inode is also supported in newer kernels.