Intruiging bits in the nsys kernel

Some answers to Warren's queries: mknod(II) first shows up in the Fourth Edition; the manual entry is dated 8/5/73. (That having been typed in the US, presumably it means 5 Aug 1973.) getgid(II) shows in the same manual, but with an older date: 3/15/72. This is also the edition in which the documentation for stat(II) first admits a group ID as well as a user ID. Both my hazy memory (made worse by lack of sleep right now) and the clues in the manual suggest that 3e/4e was the period when the system was rewritten in C; e.g. 4e is the first to show C interfaces in section II, complete with structs as well as pure byte-offset descriptions for objects like that filled in by stat, though the structs are nameless, presumably because there were no standard header files yet. Evidently the file system upheaval occurred in the same period. Reading the description of the 3e file system, I see it has been too long since I've read it. A summary: Blocks 0 and 1 are the super-block, consisting of size of free-storage bitmap the map itself size of free-i-node map the map itself Block 2 begins the i-list; data blocks follow. I-nodes 1-40 are reserved for special (device) files, and don't appear in the map. I-node 41 is the root. I-nodes have flags, a link count, a userid, a 16-bit size, creation and modification times, and eight block pointers. Flag bits inclode `allocated', `large file' (the pointers are to indirect blocks), read and write permissions for user and other, set-userid, a single `executable' flag, a `directory' flag (if clear, regular file). BUGS Two blocks are not enough to handle the i- and free- storage maps for an RP02 disk pack, which contains around 10 million words. The 4e file system is more or less that in the more-familiar V6 system: Block 0 reserved for boot block Block 1 is the super-block: file-system and i-list sizes, caches of free block and i-node numbers. The free-block list is now the familiar chain of blocks list free block numbers; the free-inode list is abolished because the i-nodes all have `allocated' flags anyway. Block 2 begins the i-list. I-node 1 is the root. I-nodes differ from 3e in having a group ID,a 24-bit size, access time instead of creation time; the `directory' flag becomes a two-bit `file type' flag; group permissions appear, there are three separate `executable' flags, and set-group-ID appears. No BUGS yet, perhaps because the code was new. Notice how history repeats: 4e replaced the free-block bitmap with a list, which made it simpler to cope with huge file systems but harder to allocate blocks in a simpler order; sundry replacement file systems in the early 1980s (Berkeley FFS, Weinberger's cheap hacks in V8) restored the bitmap, because it's easier to pick a good block when you can see all the blocks available, and because by then computers had enough memory and disks were big enough that a large bitmap wasn't a burden. An anecdote may be (barely) relevant here. I remember once in the late 1980s having a chat with Lee McMahon about group IDs, and how they didn't seem to have done quite what people wanted (hence the multiple-groups-per-process stuff in most current systems, and the special semantics for the set-group-id flag on directories, and various other features that have seemed to me never to quite hit the mark). Lee told me that when Ken first put group IDs into the system, he asked Ken what they were for. Ken allegedly shrugged and said `I dunno.' Norman Wilson Received: (from major@localhost) by minnie.cs.adfa.edu.au (8.9.1/8.9.1) id DAA15137 for pups-liszt; Thu, 21 Jan 1999 03:49:52 +1100 (EST) Received: from carp.gbr.epa.gov (carp.gbr.epa.gov [204.46.159.110]) by minnie.cs.adfa.edu.au (8.9.1/8.9.1) with ESMTP id DAA15131 for <pups(a)minnie.cs.adfa.oz.au>au>; Thu, 21 Jan 1999 03:49:37 +1100 (EST) Received: (from mjenkins@localhost) by carp.gbr.epa.gov (8.8.8/8.8.8) id KAA08238; Wed, 20 Jan 1999 10:49:27 -0600 (CST) (envelope-from mjenkins) Date: Wed, 20 Jan 1999 10:49:27 -0600 (CST) From: Mike Jenkins <mjenkins(a)carp.gbr.epa.gov> Message-Id: <199901201649.KAA08238(a)carp.gbr.epa.gov> To: pups(a)minnie.cs.adfa.oz.au Subject: Re: Old pic of ken and dmr Cc: wkt(a)cs.adfa.oz.au In-Reply-To: <199901200346.OAA06481(a)henry.cs.adfa.edu.au> Sender: owner-pups(a)minnie.cs.adfa.edu.au Precedence: bulk There is a smaller (26K) gif version on the following page: http://www.lucent.com/museum/1969unix.html The URL for the gif is: http://www.lucent.com/museum/images/1950/1969rt.gif Mike