On Fri, 2 Jul 2010 09:32:01 -0400, Thomas David Rivers <riv...@dignus.com> wrote:
>I believe the advisory locking is very "old hat" (i.e. >BSD 2, SYSV, etc...), and the more modern/proper way >to get a file lock is to use: > > fcntl(fd, F_GETLK, ...); > > fcntl(fd, F_SETLK, ...); > >This is not an 'advisory lock' like flock(), but a lock >in the operating/file system. > Does UNIX or the file system automatically issue that fcntl for the program when it accesses a file? If not, it is "advisory" in the same sense that flock is, because if the program does not issue the fcntl, it has no serialization. On the other hand, ENQ/DEQ is also advisory. The program accessing the resource needs to issue the appropriate ENQ and DEQ in order to maintain proper serialization. The question then becomes "what is the program?" For the case of the SYSDSN ENQ, the relevant program is in most cases Allocation, not the program that's going to use the data set, and the specific ENQ is based on the allocation DISP parameter. The SYSDSN ENQ is still advisory as far as Allocation is concerned, but out of the control of most data-accessing programs and thus mandatory from their perspective. If you consider ENQs such as the one ISPF created to protect updating members of a partitioned data set, and that some other programs also use, that ENQ is more obviously advisory. -- Walt Farrell IBM STSM, z/OS Security Design ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
