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fs_mgr: overlayfs: documentation: update kernel patch details

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Confusion has occurred with respect to the kernel patch requirements,
added some clarity.

Corrected some spelling mistakes in other areas.

Test: inspect gitties and run spell
Bug: 118225373
Change-Id: I4ff9497aa5a584b20e9cb2028342aa4e7e4660c3
This commit is contained in:
Mark Salyzyn 2019-02-08 07:51:01 -08:00
parent 2210f80e48
commit 60d5467bd8
1 changed files with 8 additions and 3 deletions
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11
fs_mgr/README.overlayfs.md
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@ -74,7 +74,7 @@ a probe of the filesystem types and space remaining.
When *overlayfs* logic is feasible, it will use either the
**/cache/overlay/** directory for non-A/B devices, or the
**/mnt/scratch/overlay** directory for A/B devices that have
access to *Logical Resizeable Android Partitions*.
access to *Logical Resizable Android Partitions*.
The backing store is used as soon as possible in the boot
process and can occur at first stage init, or at the
mount_all init rc commands.
@ -94,12 +94,17 @@ Caveats
and thus free dynamic partition space.
- Kernel must have CONFIG_OVERLAY_FS=y and will need to be patched
with "*overlayfs: override_creds=off option bypass creator_cred*"
if higher than 4.6.
if kernel is higher than 4.6.
The patch is available on the upstream mailing list and the latest as of
Feb 8 2019 is https://lore.kernel.org/patchwork/patch/1009299/.
This patch adds an override_creds _mount_ option to overlayfs that
permits legacy behavior for systems that do not have overlapping
sepolicy rules, principals of least privilege, which is how Android behaves.
- *adb enable-verity* will free up overlayfs and as a bonus the
device will be reverted pristine to before any content was updated.
Update engine does not take advantage of this, will perform a full OTA.
- Update engine may not run if *fs_mgr_overlayfs_is_setup*() reports
true as adb remount overrides are incompatable with an OTA resources.
true as adb remount overrides are incompatible with an OTA resources.
- For implementation simplicity on retrofit dynamic partition devices,
take the whole alternate super (eg: if "*a*" slot, then the whole of
"*system_b*").