use scenario for overlay FS

use scenario for overlay FS

[Iyad Qumei]

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

Re: use scenario for overlay FS

[A. Wan]

> 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

Re: use scenario for overlay FS

[Iyad Qumei]

> 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
>
>
>
>
>

Re: use scenario for overlay FS

[A. Wan]

Iyad wrote:
> 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:
>> 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

When they made upperdir= optional they also changed lowerdir= to allow a
(colon separated?) stack of directories.  I don't remember if they are
stacked from left to right or right to left.  I am sure it is in the
latest documentation.

Alex