On Tue, May 10, 2016 at 09:57:48AM +0100, Daniel P. Berrange wrote: > On Tue, May 10, 2016 at 10:50:40AM +0800, Fam Zheng wrote: > > They are wrappers of POSIX fcntl file locking, with the additional > > interception of open/close (through qemu_open and qemu_close) to offer a > > better semantics that preserves the locks across multiple life cycles of > > different fds on the same file. The reason to make this semantics > > change over the fcntl locks is to make the API cleaner for QEMU > > subsystems. > > > > More precisely, we remove this "feature" of fcntl lock: > > > > If a process closes any file descriptor referring to a file, then > > all of the process's locks on that file are released, regardless of > > the file descriptor(s) on which the locks were obtained. > > > > as long as the fd is always open/closed through qemu_open and > > qemu_close. > > You're not actually really removing that problem - this is just hacking > around it in a manner which is racy & susceptible to silent failure.
Whatever happened to file-private locks (https://lwn.net/Articles/586904/)? My very recent glibc doesn't appear to include them, unless the final standard used something different from `F_SETLKPW'. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top
