bcachefs: setting bcachefs_effective.* xattrs is a noop

bcachefs_effective.* xattrs show the options inherited from parent
directories (as well as explicitly set); this namespace is not for
setting bcachefs options.

Change the .set() handler to a noop so that if e.g. rsync is copying
xattrs it'll do the right thing, and only copy xattrs in the bcachefs.*
namespace. We don't want to return an error, because that will cause
rsync to bail out or get spammy.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/xattr.c

@@ -612,10 +612,20 @@ static int bch2_xattr_bcachefs_get_effective(
 					 name, buffer, size, true);
 }
 
+/* Noop - xattrs in the bcachefs_effective namespace are inherited */
+static int bch2_xattr_bcachefs_set_effective(const struct xattr_handler *handler,
+				   struct mnt_idmap *idmap,
+				   struct dentry *dentry, struct inode *vinode,
+				   const char *name, const void *value,
+				   size_t size, int flags)
+{
+	return 0;
+}
+
 static const struct xattr_handler bch_xattr_bcachefs_effective_handler = {
 	.prefix	= "bcachefs_effective.",
 	.get	= bch2_xattr_bcachefs_get_effective,
-	.set	= bch2_xattr_bcachefs_set,
+	.set	= bch2_xattr_bcachefs_set_effective,
 };
 
 #endif /* NO_BCACHEFS_FS */