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Diffstat (limited to 'pkg/sentry/fs/README.md')
| -rw-r--r-- | pkg/sentry/fs/README.md | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/pkg/sentry/fs/README.md b/pkg/sentry/fs/README.md index 76638cdae..7680187f4 100644 --- a/pkg/sentry/fs/README.md +++ b/pkg/sentry/fs/README.md @@ -193,6 +193,18 @@ interface. It multiplexes between upper and lower directory memory mappings and stores a copy of memory references so they can be transferred to the upper directory `fs.Mappable` when the file is copied up. +The lower filesystem in an overlay may contain another (nested) overlay, but the +upper filesystem may not contain another overlay. In other words, nested +overlays form a tree structure that only allows branching in the lower +filesystem. + +Caching decisions in the overlay are delegated to the upper filesystem, meaning +that the Keep and Revalidate methods on the overlay return the same values as +the upper filesystem. A small wrinkle is that the lower filesystem is not +allowed to return `true` from Revalidate, as the overlay can not reload inodes +from the lower filesystem. A lower filesystem that does return `true` from +Revalidate will trigger a panic. + The `fs.Inode` also holds a reference to a `fs.MountedFilesystem` that normalizes across the mounted filesystem state of the upper and lower directories. |