Again, Alan, why exclusive write mode? Do you mean EW? Or that this sequence be followed: (userid with class E has storage greater than the end of the desired segment). (userid with class E): DEFSEG LINFILES..... SR .... (userid with class E): load up the segment through whatever means ... (userid with class E): SAVESEG LINFILES
Now you have a shared read only segment. No changes can be made to the collective. Changing the contents of the segment means I think unmounting the block dcss device from all users, purging the segment, and then doing the sequence again, then remounting the block dcss device..
There is no "one write user multiple read users" segment designation .... unless you're CP of course. Maybe there needs to be!
On the question of SW segments it is up to the code (os) to enforce locking mechanisms.
David Kreuter
Alan Altmark wrote:
On Monday, 02/16/2004 at 02:09 CST, Adam Thornton <[EMAIL PROTECTED]> wrote:
So I have a guest whose /usr I want to freeze and stick into a DCSS.
I can easily do this if the DCSS is SW or EW.
But I really want an SR DCSS, since I want everyone to share the filesystem but I don't want anyone (except the owner) to write to it ever, and the owner only to do so very infrequently.
Can I modify the permissions on a DCSS to do this?
If not, how can I do the initial load of the DCSS?
Rick Troth has a way of doing it where he mounts a scratch disk, mounts a file via the loopback driver, and then copies the filesystem into the file on the scratch disk. Then he uses FTP or something like that to get the file into CMS space, and then a pipeline to force the contents of the file into storage. All this before the SAVESEG.
That seems a little kludgey to me. Especially since if I have the segment W, I can just mount /proc/dcssblk/SHRUSR and do a "cp -a" to load it up. But then I don't know how, having done that and then saved the segment, I can prevent anyone else from writing the segment.
Help?
Did you try the sequence I gave last week? The trick, I believe, is to load the SR segment in exclusive write mode, which gives you a private non-shared r/w copy of a r/o DCSS. When you do that, mount it, fill it, and save it, no one can change the segment. At most they, too, can load an exclusive write copy which is really a private copy.
So, don't define it SW. Define it SR.
Alan Altmark Sr. Software Engineer IBM z/VM Development
