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61 lines
2.1 KiB
Markdown
61 lines
2.1 KiB
Markdown
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Objective
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=========
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A high-performance FUSE API that minimizes pitfalls with writing
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correct filesystems.
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Decisions
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=========
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* Nodes contain references to their children. This is useful
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because most filesystems will need to construct tree-like
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structures.
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* Nodes contain references to their parents. As a result, we can
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derive the path for each Inode, and there is no need for a
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separate PathFS.
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* Nodes can be "persistent", meaning their lifetime is not under
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control of the kernel. This is useful for constructing FS trees
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in advance, rather than driven by LOOKUP.
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* The NodeID for FS tree node must be defined on creation and are
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immutable. By contrast, reusing NodeIds (eg. rsc/bazil FUSE, as
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well as old go-fuse/fuse/nodefs) needs extra synchronization to
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avoid races with notify and FORGET, and makes handling the inode
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Generation more complicated.
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* The mode of an Inode is defined on creation. Files cannot change
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type during their lifetime. This also prevents the common error
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of forgetting to return the filetype in Lookup/GetAttr.
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* The NodeID (used for communicating with kernel) is equal to
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Attr.Ino (value shown in Stat and Lstat return values.).
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* No global treelock, to ensure scalability.
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* Support for hard links. libfuse doesn't support this in the
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high-level API. Extra care for race conditions is needed when
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looking up the same file through different paths.
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* do not issue Notify{Entry,Delete} as part of
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AddChild/RmChild/MvChild: because NodeIDs are unique and
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immutable, there is no confusion about which nodes are
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invalidated, and the notification doesn't have to happen under
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lock.
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* Directory reading uses the DirStream. Semantics for rewinding
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directory reads, and adding files after opening (but before
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reading) are handled automatically. No support for directory
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seeks.
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* Method names are based on syscall names. Where there is no
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syscall (eg. "open directory"), we bias towards writing
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everything together (Opendir)
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To do/To decide
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=========
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* Symlink []byte vs string.
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