linux-kernel - Re: [PATCH v2] powerpc/fadump: return error when fadump registration fails

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Message-ID: <87bmqa62ti.fsf@concordia.ellerman.id.au>
Date:   Tue, 30 May 2017 20:45:13 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Mahesh Jagannath Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Michal Suchanek <msuchanek@...e.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Colin Ian King <colin.king@...onical.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] powerpc/fadump: return error when fadump registration fails

Mahesh Jagannath Salgaonkar <mahesh@...ux.vnet.ibm.com> writes:

> On 05/27/2017 09:16 PM, Michal Suchanek wrote:
>>  - log an error message when registration fails and no error code listed
>>  in the switch is returned
>>  - translate the hv error code to posix error code and return it from
>>  fw_register
>>  - return the posix error code from fw_register to the process writing
>>  to sysfs
>>  - return EEXIST on re-registration
>>  - return success on deregistration when fadump is not registered
>>  - return ENODEV when no memory is reserved for fadump
>
> Why do we need this ?

Because that's how we do error handling.

> Userspace can always read back the fadump registration status from
> /sys/kernel/fadump_registered (after echo 1 to it) to find out
> whether fadump registration succeeded or not.

That's a terrible API.

If we followed that example, open() wouldn't return a value, you'd have
to do another syscall to check if it worked.

I'd appreciate if someone could test this and give me a Tested-by.

cheers