Amit K. Arora wrote:

This is to give a heads up on few patches that we will be soon coming up
with. These patches implement a new system call sys_fallocate() and a
new inode operation "fallocate", for persistent preallocation. The new
system call, as Andrew suggested, will look like:

  asmlinkage long sys_fallocate(int fd, loff_t offset, loff_t len);

One thing I'd like to see is a cmd argument as well, to allow for 
example allocation vs. reservation (i.e. allocating blocks vs. simply 
reserving a number), as well as the inverse of those functions 
(un-reservation, de-allocation)?

If the allocation interface allows allocation/reservation within 
arbitrary ranges, if the only way to un-allocate is via a truncate, 
that's pretty asymmetric.

-Eric