> This implementation copies the AIX system call of the same name. Including 
> the requirement that the file descriptor be open for write for this call. 
> The call will cause the data in the range to be written, and also cause 
> some file metadata to be written.

is the AIX version a cancellation point?

at least, not listed here:
http://publib16.boulder.ibm.com/pseries/en_US/aixprggd/genprogc/term_threads.htm

YAMAMOTO Takashi