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http://cs.jhu.edu/~razvanm/fs-expedition/tux3.html
Circos. Circos is a visualization tool by Martin Krzywinski. The initial purpose was to provide a better representation of various genomic data but the program was successfully used to produce very nice graphical representations of other type of data.
Let's now look at our plot. On the outer edge we have the file systems split in categories (from top to bottom: disk-based, optical mediums, flash-based, network-based, cluster-based, memory-based, ancient). The size is proportional with the number of external symbols. Colors indicate the type of external symbols. The green represents functions, red is data, orange are read-only data, and light yellow is uninitialized data (BSS). To give a sense of proportions, the external symbols exported by the Linux Kernel, vmlinux, are also depicted. It was compiled in the same configuration as the rest of the file systems. To give some numbers: it exports a total of 9310 external symbols out of which 8047 are functions, 621 are writable variables, 159 are read-only and 483 are BSS data. The gray area from file systems indicates the external symbols which are not satisfied by the kernel but by some other kernel module. This is noticeable for nfs, nfsd and also the users of jbd/jbd2: ext3, ext4, ocfs2.
On the inner edge of vmlinux there is a plot that indicates the frequency which which each exported symbol is used by the file systems from right. One thing we noticed here is that variables are used pretty much with the same frequency as the functions.
The set of boxes from the inner edge of the file systems represents the percentage of the external symbols which are unique to each file system. We can see that virtually all the external symbols used by proc are only used by it. But having unique external symbols is not a rare feature: with the exception of ancient file systems all the other categories have members with various degree of "uniqueness".
The red arcs from inside depict the use-provide relationships between the file systems. As expected, the memory-based modules are the ones that are the main providers with proc and debufgs being the most popular one. We can also see that lockd is used by nfs and nfsd and also the relation between fat and vfat/msdos. A notable thing: there is no link between dlm and ocfs2/gfs2 because only the main kernel module was considered.