Does the virtual filesystem work on top of character devices and network subsystems?

Question

Does the virtual filesystem work on top of character devices and network subsystems, or just on top of filesystems and block devices?

Could you also explain a bit about in what sense "the VFS is working on top of" something mean?

Thanks.

A figure from Linux Device Driver seems to say no.

A figure from wikipedia seems to say yes:

presumably the color-coding in the wikipedia picture means something? — Jeff Schaller, Oct 16 '18 at 15:18
Wikipedia means all those strange type of files can be accessed through VFS, not just normal block-device filesystems — 炸鱼薯条德里克, Oct 16 '18 at 15:42
It means kernel expose interface that let you access all those things — 炸鱼薯条德里克, Oct 16 '18 at 15:58

score 1 · Answer 1 · answered Oct 16 '18 at 15:37

A virtual filesystem that is based on modern mmap technologies works as a intermediate layer between the foreground memory and the background memory.

On SunOS (this is where the concept is from) there is a generic layer called segvn which is the generic vnode segement driver and a VFS implementation uses segvn to get callbacks from memory faults (typically missing data from the background memory). The background memory used by local filesystems is typically a block device driver, but a VFS may implement anything appropriate, e.g. calling network IO.

So what a VFS implementation actually does is to implement a store method for data that manages to link a data element in the filesystem namespace to e.g. a block on a background storage device.

Does the virtual filesystem work on top of character devices and network subsystems?

1 Answers1