[pbs-devel] [PATCH v3 proxmox-backup 0/9] fix #5982: check atime update is honored

[Christian Ebner]

These patches add a check to phase 1 of garbage collection in order
to detect when the filesystem backing the chunk store does not honor
atime updates. This avoids possible data loss for situations where
garbage collection could otherwise delete chunks still referenced by
a backup snaphost's index file.

The check is performed by inserting a fixed size 4 MiB unencrypted and
compressed chunk of all-zeros. The check is performed by setting the
atime to 1 second in the past followed by setting it to now in order to
test if atime updates are honored immediately. The test is performed
on datastore creation for early detection and before garbage collection
phase 1. The test is enabled by default, but an opt-out option can be
set via the datastore tuning parameters for backwards compatibility.

Further, add a datastore tuning parameter to reduce the wait period for
chunk removal in phase 2 of garbage collection. Make this conditional on
the atime update check being enabled and successful, to avoid possible
data loss.

Most notable changes sice version 1 (thanks Fabian and Thomas for
comments and suggestions):
- Take into account Linux timestamp granularity, do not set timestamp
  to the past, as that introduces other error paths such as lack of
  permissions or fs limitations.
- Check relatime behavior, if atime behaviour is not honored. Fallback
  to original cutoff in that case.
- Adapt tuning parameter names.

Most notable changes sice version 1 (thanks Fabian and Thomas for
comments and suggestions):
- Optimize check by using the all zero chunk
- Enable the check by default and fail GC job if not honored, but allow
  to opt-out
- Add GC wait period tuning option

Link to the issue in the bugtracker:
https://bugzilla.proxmox.com/show_bug.cgi?id=5982

proxmox:

Christian Ebner (2):
  pbs api types: add garbage collection atime safety check flag
  pbs api types: add option to set GC chunk cleanup atime cutoff

 pbs-api-types/src/datastore.rs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

proxmox-backup:

Christian Ebner (7):
  datastore: use libc's timespec constants instead of redefinition
  fix #5982: garbage collection: check atime updates are honored
  ui: expose GC atime safety check flag in datastore tuning options
  docs: mention GC atime update check for tuning options
  datastore: conditionally use custom GC atime cutoff if set
  ui: expose GC atime cutoff in datastore tuning option
  docs: mention gc-atime-cutoff as datastore tuning option

 docs/storage.rst                 |  19 +++-
 pbs-datastore/src/chunk_store.rs | 144 ++++++++++++++++++++++++++++---
 pbs-datastore/src/datastore.rs   |  32 +++++++
 src/api2/config/datastore.rs     |   1 +
 www/Utils.js                     |   9 ++
 www/datastore/OptionView.js      |  17 ++++
 6 files changed, 208 insertions(+), 14 deletions(-)

-- 
2.39.5