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

[Ulrich Windl]

>>> "Ulrich Windl" <Ulrich.Windl at rz.uni-regensburg.de> schrieb am 03.08.2022
um
08:02 in Nachricht <62EA0F62020000A10004C0E7 at gwsmtp.uni-regensburg.de>:
>>>> Ken Gaillot <kgaillot at redhat.com> schrieb am 02.08.2022 um 16:09 in
> Nachricht
> <0a2125a43bbfc09d2ca5bad1a693710f00e33731.camel at redhat.com>:
>> On Tue, 2022-08-02 at 19:13 +0900, 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 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
>>> 
>>> Best Regards,
>>> Kazunori INOUE
>> 
>> I agree, it makes sense to use O_DIRECT when available. I don't think
>> an option is necessary.
>> 
>> However, O_DIRECT is not available on all OSes, so the configure script
>> should detect support. Also, it is not supported by all filesystems, so
>> if the open fails, we should retry without O_DIRECT.
> 
> I just looked it up: It seems POSIX has O_RSYNC and O_SYNC and O_DSYNC)
> instead.

I missed an opening paren: "I just looked it up: It seems POSIX has O_RSYNC
(and O_SYNC and O_DSYNC) ..."

> The buffer cache handling may be different though.
> 
> Regards,
> Ulrich
> 
>> -- 
>> Ken Gaillot <kgaillot at redhat.com>
>> 
>> _______________________________________________
>> 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/