[ClusterLabs] Antw: [EXT] Re: Q: About a false negative of storage_mon

[Fabio M. Di Nitto]

On 02/08/2022 14.37, Ulrich Windl wrote:
>>>> "Fabio M. Di Nitto" <fabbione at fabbione.net> schrieb am 02.08.2022 um 14:30
> in
> Nachricht <0b26c097-1e21-3945-24ba-355cd0ccf7f0 at fabbione.net>:
>> Hello Kazunori-san,
>>
>> On 02/08/2022 12.13, 井上和徳 wrote:
>>> Hi,
>>>
>>> Since O_DIRECT is not specified in open() [1], it reads the buffer cache
> and
>>> may result in a false negative. I fear that this possibility increases
>>> in environments with large buffer cache and running disk-reading
>> applications
>>> such as database.
>>>
>>> So, I think it's better to specify O_RDONLY|O_DIRECT, but what about it?
>>> (in this case, lseek() processing is unnecessary.)
>>
>> I will have to defer to Christine (in CC) to this email on why we didn´t
>> use O_DIRECT.
>>
>> I have a vague recollection that some storage devices didn´t like the
>> O_DIRECT option causing other issues later, but it´s been a while since
>> I touched the code.
> 
> The thing with O_DIRECT is that a "software block" has to be a multiple of a
> "hardware block"; i.e: you cannot read a partial block, and the buffer has some
> alignment requirements.
> 

that was it! thanks for refreshing my memory.

Fabio

>>
>>>
>>> # I am ready to create a patch that works with O_DIRECT. Also, I wouldn't
>> mind
>>> # a "change to add a new mode of inspection with O_DIRECT
>>> # (add a option to storage_mon) while keeping the current inspection
>> process".
>>>
>>> [1]
>>
> https://github.com/ClusterLabs/resource-agents/blob/main/tools/storage_mon.c#
> 
>> L47-L90
>>
>> It might be a very reasonable solution, tho let´s wait for an answer
>> from Chrissie.
>>
>> Cheers
>> Fabio
>> _______________________________________________
>> Manage your subscription:
>> https://lists.clusterlabs.org/mailman/listinfo/users
>>
>> ClusterLabs home: https://www.clusterlabs.org/
> 
> 
> 
> _______________________________________________
> Manage your subscription:
> https://lists.clusterlabs.org/mailman/listinfo/users
> 
> ClusterLabs home: https://www.clusterlabs.org/