Re: fcntl(F GETLEASE) semantics??

[Trond Myklebust]

to den 11.08.2005 Klokka 15:22 (+0200) skreiv Michael Kerrisk:

> As noted already, I don't know much of CIFS and SAMBA.
> But are you saying that it is sensible and consistent that
> "a process can open a file read-write, and can't place a 
> read lease, but can place a write lease"?  

It is just as "sensible and consistent" as being able to open the file
read-write and being able to place a read lease but not a write lease.
What is your point?

Make no mistake: this is not a locking protocol. It is implementing
support for a _caching_ protocol.

> This is precisely the point of the problem.  Stephen 
> Rothwell, and Matthew Wilcox seem to be saying that
> the last bit is not the case.  

The NFSv4 spec explicitly states that

  When a client has a read open delegation, it may not make any changes
  to the contents or attributes of the file but it is assured that no
  other client may do so.  When a client has a write open delegation,
  it may modify the file data since no other client will be accessing
  the file's data.  The client holding a write delegation may only
  affect file attributes which are intimately connected with the file
  data:  size, time_modify, change.

so NFSv4 cannot currently support this behaviour. If CIFS supports it,
then maybe we have a case for going to the IETF and asking for a
clarification to implement the same behaviour in NFSv4.

Cheers,
  Trond

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