Major Description
The sys_fallocate() syscall was introduced to the linux kernel in the 2.6.24 kernel. There is also an ext4_fallocate() method added in this same kernel release. This has been available in vendor kernels since RHEL 5.4.
We need to implement an fallocate() method for llite, and transport this to the OSTs to interface with the underlying OSD's fallocate() code (for ldiskfs, ZFS has no such method).
The FALLOC_FL_PUNCH_HOLE functionality of fallocate() fits very nicely with the OST_PUNCH RPC, since this was anticipated in Lustre from the beginning. The actual space reservation might also use OST_PUNCH or OST_WRITE, or we might consider a new OST_PREALLOC RPC, depending on what fits best.