[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]
Re: fcntl & cmsg
On Sep 19, 2014, at 12:38 PM, James K. Lowden
> "The received descriptor is a duplicate of the sender's
> descriptor, as if it were created with a call to dup(2). Per-process
> descriptor flags, set with fcntl(2), are not passed to a receiver."
is the descriptor sharing the its reference with another descriptor (which
happens with dup(2)/dup(2)) or did get a separate reference via a open or
if you have a dup'ed file descriptor, setting an attribute on it affects all
the other descriptors dup'ed from it.. If you open a file multiple times, each
descriptor is a separate reference and setting an attribute on one doesn't
affect the others.
There are two levels of reference involved. A descriptor indexes into a table
of file structure pointers. dup/dup2 simply duplicates file struct pointer for
one descriptor into a new slot increasing its reference count by one.
socket/open/creat allocate a new file structure and insert a pointer to the new
file structure into the table. It's this file structure which keep attribute
of a file descriptor.
Main Index |
Thread Index |