[ClusterLabs] Q: About a false negative of storage_mon

[Fabio M. Di Nitto]

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.

> 
> # 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