How to fill in the fsid for file systems?

[Andriy Gapon]

On 02/11/2018 04:24, Rick Macklem wrote:
> I have two comments. The first is related to the above and the second is a big
> picture question related to doing this.
> 
> Specifically w.r.t. the above. I probably rambled and didn't make what I was
> trying to say clear, so I'll try again...
> - getfh(2) returns a file handle that is used for NFS, but is also used for system
>   calls (fhopen(2), fhstat(2) and fhstatfs(2)) that are not related to NFS.
>   --> A file handle isn't really NFS specific, although NFS is the big user of it.
> If the above is correct, then it seems that there should only be one kind of file handle.
> --> Since the fsid is a key part of a file handle, one kind of file handle implies one
>      kind of fsid.
> I just think trying to create two kinds of fsid and two kinds of file handle would
> make the code confusing and unnecessarily complex.

As as far as I understand, VFS calls like, say, VOP_VPTOFH fill only the file ID
portion of the file handle, fh_fid.  fh_fsid is left to a caller, so potentially
we could already have a discrepancy there (but we don't).

Also, I do not think that NFS uses getfh(2), but I could be wrong.  I think that
NFS, being in kernel, directly uses VFS interfaces like the mentioned VOP_VPTOFH.

I am not sure if getfh(2) has any requirement that its result should be
compatible with anything NFS.  My impression is that it should only be usable
for fhopen(2) and the like.  But I can be wrong again.

So, if any of my assumptions is wrong, then you are right, of course, and I
should withdraw my argument.
Thanks!

-- 
Andriy Gapon