> их наличие похоже на бекдор.
> According to the glibc compat header for Irix 4, these ioctls originated
> in April 1991 as a (somewhat clunky) way to preallocate space at the end
> of a file on an EFS filesystem.  XFS, which was released in Irix 5.3 in
> December 1993, picked up these ioctls to maintain compatibility and they
> were ported to Linux in the early 2000s.
> Recently it was pointed out to me they still lurk in the kernel, even
> though the Linux fallocate syscall supplanted the functionality a long time ago.

А вот Линус считает что похоже на давно устаревший код, но никак не на бекдор
UPD: Ошибся, не Линус, а автор патча по удалению