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Thank you for the reaction, Luca, Michał. |
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I will expand my blog post soon. Thank you, Luca. |
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I want to answer the question from Michał. |
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> 1. From our talking you indicated that FUSE has both high-level and low- |
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> level API. However, the post only hints at it. Could you explain both |
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> shortly and why you've chosen the one you've chosen? |
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There are some FUSE libraries which I can choose. But actively |
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maintenanced ones are pyfuse3 and libfuse (both are developed by the |
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same person). |
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pyfuse3 is an asynchronous python library. I call it 'low-level' |
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because functions that should be implemented are called with inode |
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arguments. |
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libfuse is a C library. It has two interfaces, high-level synchronous |
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one and low-level asynchronous one. The difference between the two is |
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whether arguments are path or inode. |
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So, with the exception of libraries that are no longer maintained, the |
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only choice is pyfuse3. |
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> 2. How are you planning to deal with the essential problem that |
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> the underlying directory tree may consist of multiple filesystems with |
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> different files having colliding inode numbers? |
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VFS in the kernel and programs in userland expects consistency with |
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regard to inode, so Fusebox should provide a unique inode for each |
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file. |
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Fusebox can do this by finding out which device the file belongs to. |
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Then remember mappings from/to device-inode pairs to/from 'virtual' |
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inode. |
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However, I worried this solution hits performance since it potentially |
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causes many stat() system calls. |
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> 3. How do other passthrough filesystems deal with the same problem? |
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> What are the advantages/disadvantages of different approaches you've |
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> considered, and why did you chose this solution? |
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I investigated the high-level interface of libfuse. It caches the |
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reply of the user program. and automatically convert inode and path. |
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So the high-level interface of libfuse will affect the problem. |
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I also investigate sandboxfs ( https://github.com/bazelbuild/sandboxfs |
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). I think it take same strategy to Fusebox. |
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sandboxfs construct filesystem tree virtually on memory and notice |
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virtual inode to user application. |
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This approach may hit performance because of frequent stat() call, but |
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I cannot think better approaches. |
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Thank you for your reply and support. |
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Would you mind if I publish this mail on my blog, Michał? It was a |
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worthwhile discussion and I'd like to share it on my blog. |
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Regards, |
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Kaoru Esashika |
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