Editing CR tools

Jump to: navigation, search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision Your text
Line 1: Line 1:
See main article here [http://criu.org/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/$pid/maps'''.
 +
#* Seizes a task via relatively new ptrace interface. Seizing a task means to put it into a special state when the task have no idea if it's being operated by ptrace.
 +
#* Core parameters of a task (such as registers and friends) are being dumped via ptrace interface and parsing '''/proc/$pid/stat''' entry.
 +
#* The dumper injects a parasite code into a task via ptrace interface. This allows us to dump pages of a task right from within the task's address space. An injection procedure is pretty simple - the dumper scans executable VMA areas of a task (which were collected previously) and tests if there a place for <code>syscall</code> call, then (by ptrace as well) it substitutes an original code with <code>syscall</code> instructions and creates a new VMA area inside process address space. Finally parasite code get copied into the new VMA, the former modified code get restored.

Please note that all contributions to OpenVZ Virtuozzo Containers Wiki may be edited, altered, or removed by other contributors. If you don't want your writing to be edited mercilessly, then don't submit it here.
If you are going to add external links to an article, read the External links policy first!

To edit this page, please answer the question that appears below (more info):

Cancel Editing help (opens in new window)