Difference between inode and vnode?

BoneXXX · 07-24-2008, 08:12 AM

hi this is my first post in this forum. I would like to ask about the difference between inode and vnode. I searched on the internet and borrowed some books from the library, but I didn't quite understand it I thought maybe you can help me. Any way this is what I understood.

Tthe difference between a vnode and an inode is where it's located and when it's valid. Inodes are located on disk, vnodes in memory and inodes are always valid because they contain information that is always needed such as ownership and protection but Vnodes are located in the only exist when a file is opened.

Can someone tell me am I right or not?

In wikipedia, it says "The kernel's in-memory representation of this data is called struct inode in Linux. Systems derived from BSD use the term vnode, with the v of vnode referring to the kernel's virtual file system layer."

Are they the same things? and do they the same job?Is it a just name difference between linux and bsd OS, in linux inode in freebsd vnode?

I will really appreciate if someone can help me. Thanks.

sundialsvcs · 07-24-2008, 08:58 AM

The vnode structure ("virtual node") is an essential part of the virtual file system (VFS) support in Linux.

A definitive paper entitled "Vnodes: An Architecture for Multiple File System Types in Sun Unix," by S. R. Kleiman, can be found (says Google) at http://209.85.215.104/search?q=cache...lnk&cd=2&gl=us , which reads in part:

Quote:

The file system dependent/independent split was done just above the UNIX-kernel inode layer. This was an obvious choice, as the inode was the main object for file manipulation in the kernel. [...] The file system dependent inode was renamed vnode (virtual node). All file manipulation is done with a vnode object. Similarly, file systems are manipulated through an object called a vfs (virtual file system). The vfs is the analog to the old mount-table entry. The file system independent layer is generally referred to a the vnode layer.

In the original Unix file systems, the "actual" representation of a file (or directory or whatever) was called "an inode," and it was referenced by number. Directory entries simply contained a list of file-names and corresponding inode-numbers. This scheme exists today.

The VFS system allows filesystems of any type ... both disk-based file systems and network ones ... to be used in Unix/Linux, while retaining the essential concept of "an inode," now called "vnode." This arrangement preserves a nearly one-to-one correspondence between "the old way" and "the new way." The logical data structure, as seen and manipulated by Unix programs, exists much as it was before, and thereby insulates programs from the (possibly very enormous) actual physical differences. In typical Unix fashion, the solution is "elegant."