Passing boot logs to Linux?

[Ahmad Fatoum]

Hi,

On 03.01.24 13:44, Heinrich Schuchardt wrote:
> On 03.01.24 11:11, Csókás Bence wrote:
>> Hi,
>>
>> 2023. 12. 31. 0:54 keltezéssel, Heinrich Schuchardt írta:
>>> On 12/20/23 05:11, Simon Glass wrote:
>>>> +Heinrich Schuchardt
>>>>
>>>> On Tue, 19 Dec 2023 at 13:33, Daniel Golle <daniel at makrotopia.org>
>>>> wrote:
>>>>>
>>>>> Hi Bence,
>>>>>
>>>>> On Tue, Dec 19, 2023 at 08:08:48PM +0000, Csókás Bence wrote:
>>>>>> Hi!
>>>>>>
>>>>>> Is passing the U-Boot boot log to Linux supported yet? We are working
>>>>>> with a third-party solution, which works, but is a bit hacky, so I was
>>>>>> wondering if an official solution has been merged yet.
>>>
>>> U-Boot supports writing log messages to an rsyslog server via broadcast
>>> to UDP port 514 (CONFIG_LOG_SYSLOG=y).
>>>
>>> The device name can be set via environment variable log_hostname.
>>>
>>> If you have a log server for your devices in the same network segment,
>>> you can consolidate all your logs there.
>>>
>>> A driver writing log messages to a file could be created in U-Boot.
>>
>> I am aware, however, this is not what we want to do right now. We want
>> to pass the logs to the booted up OS on the *same* machine.
>>
>>>>>> I saw that there was an option CONFIG_CONSOLE_RECORD that saves
>>>>>> everything to a membuff, but I don't know if that can be exported to
>>>>>> Linux yet. And if not in the tree yet, would such a patch be welcome?
>>>
>>> It is not enough to export a memory buffer. There must be support in the
>>> operating system to read it.
>>
>> Of course. But it should be trivial to add a driver to Linux and other
>> FOSS OSes to support reading these records from memory.
> 
> Please, have a look at Linux'
> 
> Documentation/admin-guide/ramoops.rst
> Documentation/devicetree/bindings/reserved-memory/ramoops.yaml
> 
> If U-Boot had a log driver writing to the ramoops buffer we would not
> need any change in Linux.
> 
> The current U-Boot drivers are
> 
> common/log_syslog.c
> common/log_console.c

Yes, that's what I would suggest as well. For reference, barebox supports
pstore with ramoops backend to share its dmesg buffer with Linux.
You can take a look there for pointers. The code may not directly
portable to U-Boot though barebox implements pstore as a file system.

The problem of interactive console I/O filling up the log is resolved by having
only logged output (pr_info, dev_info and friends) output to pstore and
plain printf only prints to enabled serial consoles.

Cheers,
Ahmad

> 
> Best regards
> 
> Heinrich
> 
>>
>>> Linux supports the common platform error record (CPER) format defined in
>>> the UEFI specification. See
>>>
>>> * https://www.dmtf.org/sites/default/files/PMCI_CPEREvent_Proposal_v3.pdf
>>
>> According to page 16, records can be of the following types:
>> * error, recovered
>> * previous error
>> * simulated error
>>
>> There is no type that is an operational condition (even though you can
>> append informational sections to an error record). So what we could do
>> is mark everything as "recovered", but that is misleading, booting is
>> not an "error condition".
>>
>>  > *
>> https://uefi.org/sites/default/files/resources/Spike%20Yuan-%20Server%20RAS%20and%20UEFI%20CPER_final.pdf
>>
>> This looks like some promo material, not very useful from an
>> implementation standpoint. Plus, this talks about Intel-based cloud
>> computing/HPC, not exactly the embedded systems we are targeting.
>>
>>> Boot errors can be reported via the ACPI BERT table. But that won't help
>>> you in OpenWRT which uses device-trees.
>>
>> Exactly. I would avoid depending on ACPI/UEFI. Having a simple in-memory
>> struct can be supported on all platforms, even without ACPI, UEFI,
>> writable filesystem, even DT is not needed if you can pass the base
>> pointer to the OS via other means (ie. command line).
>>
>>> Best regards
>>>
>>> Heinrich
>>
>> Bence
>>
> 
> 

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