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Full disclosure, I am a software engineer for Arcserve, responsible for maintaining our linux kernel driver component of our data protection software suites. I am here looking for help seeking answers to two specific questions. Not knowing who to ask or really
how to communicate some of my questions, it seemed most appropriate to start my journey here with kernel newbies.
Why does the kernel only provide disk snapshot capabilities via Device Mapper (and lvm)? I am aware of multiple companies that offer linux products that come with their own kernel modules to provide full featured snapshot capabilities. Some of these linux offerings
are decades old and some are open source now. If they were to require device mapper to be setup previously, it would be difficult to insert themselves into many environments. All of the drivers seem to perform the same hook by replacing the
fops->submit_bio
(previously known as q->make_request_fn, and
more on this in the next question). It seems to me there is at least some demand for data protection functionality outside of device mapper, and this hook could be so much cleaner if it was officially supported by the kernel. (I would be thrilled to
learn that the answer is "because nobody has volunteered to write it.")
In context of Multi-Queue Block IO (blk-mq), what is the future of the older Single Queue interface? I have puzzled together some of blk-mq's history simply by interacting with it as it has become necessary; reading code and git commit messages. What I have
gleaned so far has me wondering if and when the future will be Multi-Queue only. I have read as many LWN articles I can find on the subject, but the future of IO queuing is still unclear to me.
Thank you for your time and helping me to learn how to engage with the linux kernel community. Any feedback on how and where to ask questions would also be greatly appreciated.
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