CR tools
What CRtools is
CRtools is an utility to checkpoint/restore process tree. Unlike checkpoint/restore implemented completely in kernel space, it tries to achieve the same target mostly in user space.
Agenda
- Basic design (checkpoint == proc + SEIZE, restore == syscalls + execve)
- What's required from kernel
Basic design
Checkpoint
The checkpoint procedure relies heavily on /proc file system (it's a general place where crtools takes all the information it needs). Which includes:
- Files descriptors information (via /proc/$pid/fd and /proc/$pid/fdinfo)
- Pipes parameters
- Memory maps (via /proc/$pid/maps)
The process dumper (lets call it simply the dumper further) does the following steps during checkpoint stage:
- A $pid of a process group leader is obtained from the command line
- By using this $pid the dumper walks though /proc/$pid/status and gathers children $pids recursively. At the end we will have a process tree.
- Then it takes every $pid from a process tree, sends SIGSTOP to every process found, and performs the following steps on each $pid
- Collects VMA areas by parsing /proc/$pid/maps
