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Re: [lvm-devel] vg activate/deactivate



Dne 1.5.2013 22:38, Tony Asleson napsal(a):
I was looking at implementing vg activate/deactivate in lvm2app and I
see that the function vgchange_activate will fork a polling process for
monitoring.  Doing forks in a library is discouraged so I'm soliciting
suggestions for making this work without forking a process.


Polling is only needed in some cases - i.e. when merging snapshot,
or doing pvmove operations.

However adding support for activation into lvm2app has more troubles elsewhere - the memory management issue -

if the tool is operating with i.e. root volume and suspend is involved in the activation change - we have to be sure the whole app is running in memory since after suspend - the memory paged on such device would freeze the application - this constraint is managed within lvm2 application - but so far it's not very clear how to 'export' this constraint outside.

Clearly installation process doesn't need any memory locking, since it's typically running from another boot device - so in this case we should allow to change activation state without probably any locking since we cannot be freezed by suspend - but any other use case requires some thinking.

IMHO the best here would be some 'small' daemon - which would be under full control of lvm2app and would be doing these tasks - I cannot imaging how we would memory constrain i.e. python apps consuming over >100MB.
Then you would have already solution for polling as well.

So while forking in the library is discouraged - I guess this is the case which has justification for it.

Zdenek




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