Re: Failed to open system journal: Invalid argument

[Kay One <kayone007@xxxxxxxxx>]

Hi Lennart,

Do you have any idea that UBIFS supports writable memory mappings or not?

Regards,

Karnik Jain

On Wed, May 22, 2019 at 12:05 AM Kay One <kayone007@xxxxxxxxx> wrote:

Thank you so much for your time.

Let me try changing JFFS2 to UBIFS as another available option to use for my SOC.

I would keep you guys posted.

Regards,

Karnik Jain

On Tue, May 21, 2019 at 8:18 PM Lennart Poettering <lennart@xxxxxxxxxxxxxx> wrote:

On Di, 21.05.19 17:37, Kay One (kayone007@xxxxxxxxx) wrote:

> Thanks for the reply Lennart.
>
> 1) mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 28, 0) = -1 EINVAL
> > (Invalid argument) is the culprit for this error???

Yes.

> 2) If YES. Is this JFFS2 MTD file system bug or

It's a missing feature of the fs implementation, that the journal
relies on. Memory mapping a file is not a particularly exotic feature,
and yes, file systems really should implement that.

So my recommendation would be: work with the jffs2 folks to add this
to the kernel. They already have it for PROT_READ afaik, doing it for
PROT_WRITE is extra work, and not trivial but it will fix jffs2 for
every program that uses mmap for writing, and journald is just one of
them.

> 3) Is this not considered as systemd bug to support compatibility for such
> file system? Check first FS support writable mappings or not and if not
> then use other method to enable Persistence logging for systemd?

I think it's better to fix jffs2 in this regard than to add a
userspace workaround to every single consumer of it.

Doing this without mmap() is not trivial, and I don't see anyone
stepping up to do the work. It wouldn't precisely make our codebase
easier to read either...

Lennart

--
Lennart Poettering, Berlin

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