Re: use scenario for overlay FS

[Iyad Qumei <iyad.qumei@lge.com>]

> I thought upperdir is now optional but must be read-write if one is
specified.

I have two file systems that I need to create a union for.  The upperdir 
overrides the lowerdir, hence replacing its content. Therefore, 
regardless if the upperdir is optional, I do need it in this use case.

Per the documentation:

    "A read-only overlay of two read-only filesystems may use any filesystem type."

I understood that my use case is possible. However, it does contradict 
the actual implementation,

   "overlayfs: workdir and upperdir must reside under the same mount"

and your statement, of course.

Thanks,
Iyad

On 04/20/2015 04:01 PM, A. Wan wrote:
>> Hi Neil,
>>
>> Regarding the overlayfs implementation, I am interested in overlaying
>> two squashfs file systems, read-only, and running into a problem with
>> location of the work directory:
>>
>>    "overlayfs: workdir and upperdir must reside under the same mount"
>>
>> Since the upper directory is read-only, and it is mounted on a partition
>> as such, having writable work directory is not possible. Any suggestions
>> on how to utilize overlayfs in this scenario?
>>
>> I feel this restriction is overkill for the feature.
>>
>> --
>> Thanks,
>> Iyad
> I thought upperdir is now optional but must be read-write if one is
> specified.  Therefore if you want the whole stack read-only specify only
> lowdirs and skip the upperdir.  Correct me if I am wrong.
>
> Alex
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