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45 lines
1.6 KiB
ReStructuredText
45 lines
1.6 KiB
ReStructuredText
MDS internal data structures
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==============================
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*CInode*
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CInode contains the metadata of a file, there is one CInode for each file.
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The CInode stores information like who owns the file, how big the file is.
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*CDentry*
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CDentry is the glue that holds inodes and files together by relating inode to
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file/directory names. A CDentry links to at most one CInode (it may not link
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to any CInode). A CInode may be linked by multiple CDentries.
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*CDir*
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CDir only exists for directory inode, it's used to link CDentries under the
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directory. A CInode can have multiple CDir when the directory is fragmented.
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These data structures are linked together as::
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CInode
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CDir
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CDentry CDentry
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CInode CInode
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CDir CDir
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CDentry CDentry CDentry
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CInode CInode CInode
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As this doc is being written, size of CInode is about 1400 bytes, size of CDentry
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is about 400 bytes, size of CDir is about 700 bytes. These data structures are
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quite large. Please be careful if you want to add new fields to them.
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*OpenFileTable*
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Open file table tracks open files and their ancestor directories. Recovering
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MDS can easily get open files' paths, significantly reducing the time of
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loading inodes for open files. Each entry in the table corresponds to an inode,
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it records linkage information (parent inode and dentry name) of the inode. MDS
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can constructs the inode's path by recursively lookup parent inode's linkage.
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Open file table is stored in omap of RADOS objects, table entries correspond to
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KV pairs in omap.
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