== 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/$pid/maps''') The process dumper (lets call it simply the dumper further) does the following steps during checkpoint stageSee main article here [http: # A '''$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 '''$pids''' recursivelycriu. At the end we will have a process tree.# Then it takes every '''$pid''' from a process tree, sends ''SIGSTOP'' to every process found, and performs the following steps on each '''$pid'''#* Collects VMA areas by parsing '''/proc/$pidorg/maps'''#*CR_tools]
