Re: File and Directory Change Notification

[Jamie Lokier <jamie@shareable.org>]

Joseph D. Wagner wrote:
> The docs are a little sketchy on this one.
> 
> Using fcntl(), can you get change notifications on specific files, or just 
> directories?

You can use F_NOTIFY to get notifications of all files in a directory
(the whole directory, and only for operations via this path in case of
hard links), and F_SETLEASE to get notifications of other processes
opening a file.

There's no way to be notified of every individual write to a single
file, but that isn't typically useful anyway.

What's missing from leases is the ability to block until the final
close of a file (and block further opens in the meantime), and for
F_RDLCK leases to fail/block when the file is open for writing
(there's a FIXME in the kernel lease code for that, but nobody has
fixed it).

I'm not sure why exclusive leases are always allowed but mandatory
locking isn't by default.  They seem to offer similar DOS possibilities.

-- Jamie