Re: struct file reference at VFS level

[manu%netbsd.org@localhost (Emmanuel Dreyfus)]

David Holland <dholland-tech%netbsd.org@localhost> wrote:

> If something in fuse is causing these cases to share the same open and
> thus the same struct file, fuse is broken. Fix fuse first.
> 
> If that isn't what's happening, the next possible problem is that
> puffs/refuse/whatnot is the losing IO_NDELAY flag of VOP_WRITE. If so,
> fuse is broken. Fix fuse first.

If you want to implement mandatory locks, the O_NONBLOCK / IO_NDELAY
just determines how a failure should occur: by waiting for the lock to
be released, or by failing with EAGAIN.

In order to decide whether an I/O will succeed or fail because of a
mandatory lock, the filesystem must know if there is a lock on the file,
and in the case there is a lock, whether it is held by the caller or
not.

As I understand, telling if a lock is held by caller requires a
reference to the struct file on which the operation was issued.

If we reconsider the proposed scenario without process 2 using
O_NONBLOCK, then a write by process 2 must wait for the lock to be
released, while a write by process 1 must succeed without delay. But
when the requests come at the filesystem level, there is no way to
distinguish them.

-- 
Emmanuel Dreyfus
http://hcpnet.free.fr/pubz
manu%netbsd.org@localhost