[systemd-devel] [PATCHv4 0/3] resume: implement support for resuming from hibernation

[Ivan Shapovalov]

This patchset allows systemd to parse resume= kernel command line parameter
and initiate resume from the specified device.

It adds:
- a 'systemd-resume' tool which takes path to a device node and
  writes its major:minor to /sys/power/state;
- a corresponding 'systemd-resume at .service' templated unit;
- a 'systemd-resume-generator' generator which parses the kernel command line
  and instantiates the unit as necessary.

This functionality already exists in-kernel, but only for "/dev/sdXY"-style
pathes. Implementing it in userspace allows to use arbitrary udev-created
symlinks, e. g. persistent block device pathes ("/dev/disk/by-foo/bar").

Userspace parsing of resume= kernel command line parameter has been
traditionally done in initramfs via shell scripts (for Arch Linux, this is
"resume" mkinitcpio hook), so I feel that this feature has its place within
systemd.

Due to the nature of hibernation, the resume unit must be activated before
any modifications to filesystems take place. This can happen only in initramfs
before mounting anything.

So, first patch orders all non-root fsck after local-fs-pre.target, which in
turn allows to order the resume unit before those fsck instances.

Second and third patches add the tool, the unit and the generator.

Thanks for reviewing!

v2: fix issues pointed out by Andrei:
    - don't RemainAfterExit because it's useless
    - don't attempt to resume outside of initramfs because it's unsafe
      (reiserfs replays journal even if mounted RO)

v3: fix mistakes spotted by Thomas:
    - return 0 in main path of resume.c:process_resume()
    - fix type and add missing cleanup attribute in resume-generator.c:main()

v4: drop the [RFC] prefix as there are no more issues with this approach;
    incorporate feedback from Lennart:
    - fix indentation in resume-generator.c:parse_proc_cmdline_item()
    - remove overly aggressive 80-column line breaks
    - don't Before=usr.mount and After=systemd-udevd.service
      as the respective configurations are deemed broken
    - reword the "Failed to resume" message and downgrade it to log_info()

Ivan Shapovalov (3):
  units: order systemd-fsck at .service after local-fs-pre.target.
  resume: add a tool to write a device node's major:minor to /sys/power/resume.
  resume-generator: add a generator for instantiating the resume unit.

 Makefile-man.am                         |  9 ++++
 Makefile.am                             | 28 ++++++++--
 man/kernel-command-line.xml             | 13 ++++-
 man/systemd-resume-generator.xml        | 91 +++++++++++++++++++++++++++++++
 man/systemd-resume at .service.xml         | 81 ++++++++++++++++++++++++++++
 src/resume-generator/Makefile           |  1 +
 src/resume-generator/resume-generator.c | 95 +++++++++++++++++++++++++++++++++
 src/resume/Makefile                     |  1 +
 src/resume/resume.c                     | 81 ++++++++++++++++++++++++++++
 units/systemd-fsck at .service.in          |  2 +-
 units/systemd-resume at .service.in        | 20 +++++++
 11 files changed, 416 insertions(+), 6 deletions(-)
 create mode 100644 man/systemd-resume-generator.xml
 create mode 100644 man/systemd-resume at .service.xml
 create mode 120000 src/resume-generator/Makefile
 create mode 100644 src/resume-generator/resume-generator.c
 create mode 120000 src/resume/Makefile
 create mode 100644 src/resume/resume.c
 create mode 100644 units/systemd-resume at .service.in

-- 
2.1.0