Allow writable /var and /etc directories
#2522
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| #define VAR_OVERLAY_PATH OVERLAY_PATH "/var" | ||
| #define ETC_OVERLAY_PATH OVERLAY_PATH "/etc" | ||
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| const struct InitOp overlay_ops[] = { |
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Would hard-coding this be restrictive?
Say tomorrow somebody wants to write logs to /tmp and want it to be overlay.
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yes, but the flipside would be the complexity of C code needed to handle parsing and validating a list of user-provided directories from the command line
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True, but we will future proof this so that we don't need code change every time new directory needs to be writable.
Should we pass something like "--overlay-dirs=/etc,/var,/opt" to init process?
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we can always add that in the future, but i think the long option parsing and additional path validation would over-complicate this already complicated PR
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Binaries in the uVM can require writing to (or be configured by) files in `/var` (or `/etc`, respectively). An LCOW uVM VHD-backed rootfs, however, is readonly (as opposed to WCOW, which creates a new snapshot and therefor scratch VHD per uVM). Remedy this by creating `overlay` mounts for the two directories, enabled by the `/init` flag `-w`. Use `overlay` instead of creating a `tmpfs` mount directly over the directories (which is done for `/run` and `/tmp`) to preserve existing content in the rootfs. Add a new `WritableOverlayDirs` annotation to enable the feature. Make the annotation internal (unpublished) since: - it is implementation dependent (i.e., how LCOW uVMs are run could conceivably change in the future); and - the feature is aimed at more advanced use cases where users are modifying the LCOW uVMs rootfs and should be familiar with `hcshims`'s inner workings Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>
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Binaries in the uVM can require writing to (or be configured by) files in
/var(or/etc, respectively).An LCOW uVM VHD-backed rootfs, however, is readonly (as opposed to WCOW, which creates a new snapshot and therefor scratch VHD per uVM). Remedy this by creating
overlaymounts for the two directories, enabled by the/initflag-w.Use
overlayinstead of creating atmpfsmount directly over the directories (which is done for/runand/tmp) to preserve existing content in the rootfs.Add a new
WritableOverlayDirsannotation to enable the feature. Make the annotation internal (unpublished) since:hcshims's inner workings