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Line 7: − + − − == 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/$pid/maps'''). − − The process dumper (lets call it a dumper further) does the following steps during checkpoint stage − − # A '''$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/$pid/stat''' entry. − #* The dumper injects a parasite code into a task via ptrace interface. This allows us to dump pages of a task right from within the task's address space. − #** An injection procedure is pretty simple - the dumper scans executable VMA areas of a task (which were collected previously) and tests if there a place for <code>syscall</code> call, then (by ptrace as well) it substitutes an original code with <code>syscall</code> instructions and creates a new VMA area inside process address space. − #** Finally parasite code get copied into the new VMA and the former code which was modified during parasite bootstrap procedure get restored. − #* Then (by using a parasite code) the dumper flushes contents of a task's pages to the file. And pulls out parasite code block completely, since we don't need it anymore. − #* Once parasite removed a task get unseized via ptrace call but it remains stopped still. − #* The dumper writes out files and pipes parameter and data. − # The procedure continues for every '''$pid'''. − − === Restore === − − The restore procedure (aka restorer) proceed in the following steps − − # A process tree has been read from a file. − # Every process started with saved (i.e. original) '''$pid''' via <code>clone()</code> call. − # Files and pipes are restored (by restored it's meant - they are opened and positioned). − # A new memory map is created, filled with data the program had at checkpoint time. − # Finally the program is kicked to start with rt_sigreturn system call. − − <!-- − === Kernel requirements === − − Since checkpoint and restore processes require some help from the Linux kernel, the following kernel patches are needed − − * procfs-report-eisdir-when-reading-sysctl-dirs-in-proc.patch − * proc-fix-races-against-execve-of-proc-pid-fd.patch − * proc-fix-races-against-execve-of-proc-pid-fd-fix.patch − * proc-force-dcache-drop-on-unauthorized-access.patch − * cr-statfs-callback-for-pipefs − − These patches are already in -mm tree and rather a preparation patches for the next series. − − * fs-proc-switch-to-dentry − * cr-proc-map-files-21 − − These patches introduce '''/proc/$pid/msp_files'''. − − * cr-clone-with-pid-support − − This one introduce ability to clone process with specified pid. − − * cr-proc-add-children − − This one introduce "Children" line to '''/proc/$pid/status'''. − − * fs-add-do-close − * fs-proc-add-tls − * fs-proc-add-mm-task-stat − − These ones provides missing pieces of process' information which is needed for checkpoint/restore. − − * binfmt-elf-for-cr-5 − − This one provides new Elf file format. − -->
no edit summary
# Only pure x86-64 environment is supported, no IA32 emulation allowed.
# Only pure x86-64 environment is supported, no IA32 emulation allowed.
# There is no way to use cgroups freezer facility yet.
# There is no way to use cgroups freezer facility yet.
# No network or IPC checkpoint/restore supported.
# No IPC checkpoint/restore supported, and network is under hard development stage.
== Download crtools ==
== Download crtools ==