Question

Is there anyway in Linux (or more generally in a POSIX OS) to guarantee that during the execution of a program, no file descriptors will be reused, even if a file is closed and another opened? My understanding is that this situation would usually lead to the file descriptor for the closed file being reassigned to the newly opened file.

I’m working on an I/O tracing project and it would make life simpler if I could assume that after an open()/fopen() call, all subsequent I/O to that file descriptor is to the same file.

I’ll take either a compile-time or run-time solution.

If it is not possible, I could do my own accounting when I process the trace file (noting the location of all open and close calls), but I’d prefer to squash the problem during execution of the traced program.

Answer 1

Note that POSIX requires:

The open() function shall return a file descriptor for the named file
that is the lowest file descriptor not currently open for that
process.

So in the strictest sense, your request will change the program’s environment to be no longer POSIX compliant.

That said, I think your best bet is to use the LD_PRELOAD trick to intercept calls to close and ignore them.