On Tue, May 03, 2016 at 05:33:34AM +0200, Emmanuel Dreyfus wrote: > Christoph Badura <b...@bsd.de> wrote: > > > Mandatory file locking simply is a SMOP for the kernel to add a flag to a > > vnode that indicates whether mandatory locking is in effect and adding the > > necessary checks and interaction with file systems to open(2), read(2), > > write(2) etc. at the syscall level. VOP_ADVLOCK is the right place to > > handle the necessary interaction with the file systems.[3] > > Please tell me if I understood your point of view correctly: you mean > that mandatory locks should be implemented above VFS, by turning for > instance a write operation into VOP_ADVLOCK then on success VOP_WRITE?
Yes. Mandatory locking is pretty much like: - for the read case off = current_file_offset VOP_ADVLOCK(F_RDLCK, off, size_of_read) VOP_READ(...) VOP_ADVLOCK(F_UNLCK, off, size_of_read) - for the write case off = current_file_offset VOP_ADVLOCK(F_WRLCK, off, size_of_write) VOP_WRITE(...) VOP_ADVLOCK(F_UNLCK, off, size_of_write) Except that it is unclear to me how the F_UNLCK interacts with overlapping read locks set explicitly by the process. I.e. is the pre-existing read-lock split or truncated? But I guess it is OK to have the same lossage as with advisory locks. --chris
