Re: flock

"François Revol" <[email protected]> wrote:
> > a while ago, I implemented advisory locking support to the VFS. 
> > However, I didn't add the non-POSIX flock() function; this locking 
> > functionality is only available using the POSIX defined fcntl(..., 
> > F_SETLK, ...) method.
> > Should we add flock() as well even though it's not part of POSIX?
> Beware, though fcntl(F_SETLK) uses a struct flock, this one has 
> nothing 
> to do and is not compatible with it, and has a different semantic 
> (for 
> ex one removes the lock on exec or a close, the other doesn't). I 
> scratched my head several days on them.
> This one is a BSDism, but I think several apps wants it (samba ?).

We should collect the differences and implement flock() and F_SETLK 
correctly, then.
If possible, I would prefer to have flock() done via F_SETLK, and if 
it's only the COE behaviour, I'm sure we can fix that :)

> IIRC Linux implements both via a single call with a flag to indicate 
> the semantics used, and forbids using both on the same file.
> cf. locks.txt and mandatory.txt in /usr/src/linux/Documentation/

It doesn't really go in depth - it reads more like a comparison between 
mandatory vs. advisory locking implementations. I don't want to expose 
a mandatory locking to POSIX at all, I'm not even sure if I want to 
have that in the Be API either (BNode::Lock() could also just do 
advisory locking).

> You can also add lockf() but this one is just a simple call to 
> fcntl(), 
> and might actually be already don't in glibc.

I don't want to add too much cruft :-)

Bye,
   Axel.


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