Process Table

Fork will copy a PID exactly:

However, some differences:

• %rax will have different values based on child or parent.
• PID has different number
  • getpid, also getppid which gets parent’s PID
• File descriptors will point to the same struct file, could have interesting effects

File Descriptors

• Point toward some “struct file” that has:
  • a pointer to the “fs struct” in the kernel
  • read offset
  • permissions
• The “fs struct” has information about the file irrespective of who’s opened it

What if we want some process a to talk to some process b? In other words, make fd 1 of process a talk to fd0 of process b.

a > tmpfile &
b < tmpfile

What’s wrong with this approach?

• Race conditions: what if a hasn’t finished writing?
• I/O overhead
• Waste of storage

Pipes

• Is a bounded buffer by kernel (5 KiB?)