blktap3
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Mahantesh Salimath
Dec 13, 2017, 2:30:13 PM12/13/17
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Hello,
I have been working on upgrading blktap2 to blktap3 in OpenXT (https://openxt.atlassian.net/wiki/spaces/~mahanteshais/pages/121864193/Blktap3).
The changes involve multiple existing repositories along with the introduction of new one: blktap3
The base for blktap3 is mirrored from https://github.com/xapi-project/blktap. After resolving several issues, introducing encryption support and adding other missing features, blktap3 can now be integrated into OpenXT.
An overview of blktap is given on the xen wiki page https://wiki.xenproject.org/wiki/Blktap. This page describes the objective, mechanism and source code organization of blktap inside xen tree.
The https://xenserver.org/blog/entry/tapdisk3.html blog explains in detail, the differences between all the blktap versions with concentration on blktap3 and also compares the performance differences between blktap2 and blktap3.
blktap3 is able to perform and scale better because:
> Introduction of Linux 3.x kernel into dom0 lead to the inclusion of grant device.
tapdisk3 (a user-space process) uses grant device, event channels and blkif protocol to talk directly with xen-blkfront of the guest domains.
Furthermore, tapdisk3 follows the 'grant copy' technique wherein most of the work happens in Xen hypervisor. This mechanism/technique effectively reduces the data path for disk operations resulting in better performance.
blktap3 source code maintained as part of XenServer can be found here: https://github.com/xapi-project/blktap, it seems that it is no longer supported/maintained.
The initial blktap3 repository, with patches to blktap2, can be found here: https://github.com/qiaohaiming/blktap3, as explained in the README, this lacks some of the intended functionality/features.
blktap3 repository compatible/integrated against xen-4.9.X can be found at: https://github.com/mahantesh-ais/blktap3/tree/master and the most recent OpenXT branch is at: https://github.com/mahantesh-ais/blktap3/tree/prv4
As of now, blktap3 is functional with PV and HVM guests in OpenXT, but further tests are to be carried out for any shortcomings/issues.
All the changes involved for OpenXT integration can be found here:
Build details:
Best,
Mahantesh Salimath,
Assured Information Security.
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