This is very interesting, but I think the two problems you will hit are (1) the proliferation of these "," names everywhere and what they mean (do you include them in readdir? If you do, that's going to at least triple its length; if you do not, readdir is not showing directory contents, since each file comes with "benefits"), and (2) you will eventually run into a large installed system that already uses those names -- that kind of thing happens; it will get messy.
For that reason I kind of fear the way you are overloading path names. One very good thing about the 9p stat is that it is not intended to be processed by the kernel. In most cases it gets passed up to userspace. I kind of wonder about putting this stuff in stat and wstat. In my Linux 9p from 1998, I extended stat such that, for symlinks, the string for the symlink and the target were returned (at that point, on 100mbit ethernet, that was far cheaper than a stat / readlink combo) and I set a bit in the mode to indicate it was a symlink. The kernel was none the wiser, and user mode had both names at its disposal, with the option of using or ignoring the second. Same for wstat. As for timestamps and other things, you could pull an x86_64-like hack: if there is an "extended 9p" bit in the header somewhere, then you can look further in the stat packet, beyond the length of a standard packet, for the nanosecond data, to match the second data in the standard stat. That way, code that only uses the standard stat works, but code looking for more can find it. So, I think your ",name" ideas are interesting, but I personally prefer to extend stat/wstat, because I've found plan9 overall is pretty flexible to that kind of thing. Thanks, hope to see your paper at iwp9. ron On Fri, Feb 14, 2025 at 5:20 AM Edouard Klein <e...@rdklein.fr> wrote: > This is cool :) > > Can you pass xattrs through the ,ctl file ? > > > If you can find the time to write it up in thee pages, that would be a > nice WiP for iwp9 ! The deadline has just been extended ! > > Cheers, > > Edouard. > > "Alyssa M via 9fans" <9fans@9fans.net> writes: > > > I have a complicated relationship with 9P2000.L. On the one hand it's > been a useful way to build file systems for Linux, and I've gotten some > mileage out of that. On the > > other hand, I'm not crazy about having a different protocol to 9P (I've > read through a lot of what's been said on 9fans about this, going back many > years). > > > > I've been trying an experiment over the last few weeks to see if I can > pass the extra Linux file system features over 9P (9P2000) as an > application of 9P rather than using a > > separate protocol. I want to be able to connect two Linux machines using > 9P, but have the full Linux file system semantics available across the > connection: symbolic links, > > moving files and directories around, nanosecond time stamps, open modes, > record locking, the whole bit. I also want that to work properly with a > Plan 9 machine between > > them. > > Linux programs should see a Linux file system, Plan 9 programs should > see a Plan 9 file system. > > > > I think it's easiest to explain by walking through an end-to-end example. > > > > First, I altered my Linux 9P (9P2000) file server to offer an encoding > of the linuxiness (is that a word??) For example, here's a test directory > on my Linux machine. > > > > lyssa@pibysix:~/t $ ls -l > > total 28 > > -rw-r--r-- 1 lyssa lyssa 6 Feb 8 11:41 bar > > lrwxrwxrwx 1 lyssa lyssa 6 Feb 7 22:17 bin -> ../bin > > -rw-r--r-- 1 lyssa lyssa 6 Feb 10 15:06 foo > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 15:31 foop > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 18:33 foop2 > > drwxr-xr-x 2 lyssa lyssa 4096 Feb 7 00:54 foot > > lrwxrwxrwx 1 lyssa lyssa 3 Feb 7 01:06 hello -> foo > > lrwxrwxrwx 1 lyssa lyssa 5 Feb 11 02:08 hello6 -> hello > > -rw-r--r-- 1 lyssa lyssa 38 Feb 8 00:58 hi > > lrwxrwxrwx 1 lyssa lyssa 2 Feb 9 01:28 hi2 -> hi > > lrwxrwxrwx 1 lyssa lyssa 13 Feb 11 03:20 somenewlinkname -> > one/two/three > > lyssa@pibysix:~/t $ > > > > If I mount it on Plan 9 with my 9P server, it looks like this: > > > > term% pwd > > /usr/glenda/mnt/home/lyssa/t > > term% ls -lp > > --rw-r--r-- M 1061 glenda glenda 6 Feb 8 11:41 bar > > d-rwxr-xr-x M 1061 glenda glenda 0 Feb 6 23:51 bin > > --rw-r--r-- M 1061 glenda glenda 6 Feb 10 15:06 foo > > --rw-r--r-- M 1061 glenda glenda 1 Feb 9 15:31 foop > > --rw-r--r-- M 1061 glenda glenda 1 Feb 9 18:33 foop2 > > d-rwxr-xr-x M 1061 glenda glenda 0 Feb 7 00:54 foot > > --rw-r--r-- M 1061 glenda glenda 6 Feb 10 15:06 hello > > --rw-r--r-- M 1061 glenda glenda 6 Feb 10 15:06 hello6 > > --rw-r--r-- M 1061 glenda glenda 38 Feb 8 00:58 hi > > --rw-r--r-- M 1061 glenda glenda 38 Feb 8 00:58 hi2 > > ----------- M 1061 '(0)' glenda 0 Jan 1 1970 somenewlinkname > > term% > > > > These files all behave as you might expect from a vanilla 9P server. > > (the symbolic links are followed - the bottom one is a broken link. A > long and involved conversation could be had about this, but can we not do > that right now?) > > > > I've added an invisible virtual extension to the namespace my Linux 9P > server offers: > > For any given file "/a/b/c/foo", there is a control file, > "/a/b/c/,ctl/foo" which gives access to all its linuxy gloriousness: > > > > term% cat ,ctl/foo > > dev 45831 > > inode 265868 > > mode 0100644 > > nlink 1 > > uid 1001 > > gid 1001 > > rdev 0 > > size 6 > > blksize 4096 > > blocks 8 > > atime 1739199962 > > mtime 1739199962 > > ctime 1739466812 > > atimensec 460383798 > > mtimensec 470383712 > > ctimensec 926076796 > > name foo > > term% > > > > You can also write commands into these files to change some of the > properties - as you might expect. > > Here are the control files in the (unlisted) virtual directory ",ctl": > > > > term% ls -lp ,ctl > > --rw-r--r-- M 1061 glenda glenda 0 Feb 8 11:41 bar > > --rw-r--r-- M 1061 glenda glenda 0 Feb 6 23:51 bin > > --rw-r--r-- M 1061 glenda glenda 0 Feb 10 15:06 foo > > --rw-r--r-- M 1061 glenda glenda 0 Feb 9 15:31 foop > > --rw-r--r-- M 1061 glenda glenda 0 Feb 9 18:33 foop2 > > --rw-r--r-- M 1061 glenda glenda 0 Feb 7 00:54 foot > > --rw-r--r-- M 1061 glenda glenda 0 Feb 10 15:06 hello > > --rw-r--r-- M 1061 glenda glenda 0 Feb 10 15:06 hello6 > > --rw-r--r-- M 1061 glenda glenda 0 Feb 8 00:58 hi > > --rw-r--r-- M 1061 glenda glenda 0 Feb 8 00:58 hi2 > > --rw-r--r-- M 1061 '(0)' glenda 0 Jan 1 1970 somenewlinkname > > term% > > > > ",ctl" is a simple example of a means to pass parameters down a Twalk to > later requests by using weird file names. > > You can pass other parameters... > > > > term% ls -lp ,nofollow > > --rw-r--r-- M 1061 glenda glenda 6 Feb 8 11:41 bar > > a-r--r--r-- M 1061 glenda glenda 6 Feb 7 22:17 bin > > --rw-r--r-- M 1061 glenda glenda 6 Feb 10 15:06 foo > > --rw-r--r-- M 1061 glenda glenda 1 Feb 9 15:31 foop > > --rw-r--r-- M 1061 glenda glenda 1 Feb 9 18:33 foop2 > > d-rwxr-xr-x M 1061 glenda glenda 0 Feb 7 00:54 foot > > a-r--r--r-- M 1061 glenda glenda 3 Feb 7 01:06 hello > > a-r--r--r-- M 1061 glenda glenda 5 Feb 11 02:08 hello6 > > --rw-r--r-- M 1061 glenda glenda 38 Feb 8 00:58 hi > > a-r--r--r-- M 1061 glenda glenda 2 Feb 9 01:28 hi2 > > a---------- M 1061 glenda glenda 13 Feb 11 03:20 somenewlinkname > > term% > > > > This provides a way to avoid following the symbolic links. > > Symlinks show up as append-only, read-only files, which is a bit of a > hack, I suppose, but perhaps okay for now. > > When you don't follow symlinks, they present their link target. > > > > term% cat ,nofollow/bin; echo > > ../bin > > term% > > > > And you can access the control file of a link: > > > > term% cat ,ctl,nofollow/bin > > dev 45831 > > inode 263367 > > mode 0120777 > > nlink 1 > > uid 1001 > > gid 1001 > > rdev 0 > > size 6 > > blksize 4096 > > blocks 0 > > atime 1738966670 > > mtime 1738966670 > > ctime 1738966670 > > atimensec 484184178 > > mtimensec 484184178 > > ctimensec 484184178 > > name bin > > symlink ..%2Fbin > > term% > > > > You can make new symbolic links from plan 9. > > (where's that Linux ls(1) program?) > > > > term% ls -l ../../../bin/ls > > --rwxr-xr-x M 1061 '(0)' glenda 108752 Feb 28 2019 ../../../bin/ls > > term% > > > > Let's link to it: > > > > term% echo symlink ../../../bin/ls another >,ctl/, > > term% ls -lp > > --rwxr-xr-x M 1061 '(0)' glenda 108752 Feb 28 2019 another > > --rw-r--r-- M 1061 glenda glenda 6 Feb 8 11:41 bar > > d-rwxr-xr-x M 1061 glenda glenda 0 Feb 6 23:51 bin > > --rw-r--r-- M 1061 glenda glenda 6 Feb 10 15:06 foo > > --rw-r--r-- M 1061 glenda glenda 1 Feb 9 15:31 foop > > --rw-r--r-- M 1061 glenda glenda 1 Feb 9 18:33 foop2 > > d-rwxr-xr-x M 1061 glenda glenda 0 Feb 7 00:54 foot > > --rw-r--r-- M 1061 glenda glenda 6 Feb 10 15:06 hello > > --rw-r--r-- M 1061 glenda glenda 6 Feb 10 15:06 hello6 > > --rw-r--r-- M 1061 glenda glenda 38 Feb 8 00:58 hi > > --rw-r--r-- M 1061 glenda glenda 38 Feb 8 00:58 hi2 > > ----------- M 1061 '(0)' glenda 0 Jan 1 1970 somenewlinkname > > term% > > > > ",ctl/," is a name for the control file for the directory itself. > > Commands written there can be used to make symlinks, move files, etc. > > It has an alias in the parent directory's ,ctl directory. > > > > So that's the general idea. Linux extras are hidden from Plan 9, but > accessible. > > > > Second, I built an client adapter for Linux that uses these extra > mechanisms. It serves 9P2000.L, which it mounts locally using v9fs - the > Linux 9P client, but speaks > > "9P-with-benefits" across the network as a client. I have it in mind to > do a version for FUSE one day, instead of using v9fs. > > > > Exportfs on my plan 9 machine is serving the namespace above that > included a mount of my Linux 9P server, above. > > I've mounted that on Linux in /mnt/mnt. So now Linux is looking at Plan > 9, which is looking at Linux: > > > > lyssa@pibysix:/mnt/mnt/usr/glenda/mnt/home/lyssa/t $ ls -l > > total 24 > > lrwxrwxrwx 1 lyssa lyssa 15 Feb 13 18:00 another -> ../../../bin/ls > > -rw-r--r-- 1 lyssa lyssa 6 Feb 8 11:41 bar > > lrwxrwxrwx 1 lyssa lyssa 6 Feb 7 22:17 bin -> ../bin > > -rw-r--r-- 1 lyssa lyssa 6 Feb 10 15:06 foo > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 15:31 foop > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 18:33 foop2 > > drwxr-xr-x 2 lyssa lyssa 4096 Feb 7 00:54 foot > > lrwxrwxrwx 1 lyssa lyssa 3 Feb 7 01:06 hello -> foo > > lrwxrwxrwx 1 lyssa lyssa 5 Feb 11 02:08 hello6 -> hello > > -rw-r--r-- 1 lyssa lyssa 38 Feb 8 00:58 hi > > lrwxrwxrwx 1 lyssa lyssa 2 Feb 9 01:28 hi2 -> hi > > lrwxrwxrwx 1 lyssa lyssa 13 Feb 11 03:20 somenewlinkname -> > one/two/three > > > > All that linuxy goodness is passed through Plan 9 as shown above. Linux > does not expect file systems to follow > > symbolic links themselves, so the adapter uses ",nofollow". Here's the > same directory with the links resolved by Linux: > > > > lyssa@pibysix:/mnt/mnt/usr/glenda/mnt/home/lyssa/t $ ls -lL > > total 24 > > -rwxr-xr-x 1 root root 108752 Feb 28 2019 another > > -rw-r--r-- 1 lyssa lyssa 6 Feb 8 11:41 bar > > drwxr-xr-x 2 lyssa lyssa 4096 Feb 6 23:51 bin > > -rw-r--r-- 1 lyssa lyssa 6 Feb 10 15:06 foo > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 15:31 foop > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 18:33 foop2 > > drwxr-xr-x 2 lyssa lyssa 4096 Feb 7 00:54 foot > > -rw-r--r-- 1 lyssa lyssa 6 Feb 10 15:06 hello > > -rw-r--r-- 1 lyssa lyssa 6 Feb 10 15:06 hello6 > > -rw-r--r-- 1 lyssa lyssa 38 Feb 8 00:58 hi > > -rw-r--r-- 1 lyssa lyssa 38 Feb 8 00:58 hi2 > > ?????????? ? ? ? ? ? somenewlinkname > > lyssa@pibysix:/mnt/mnt/usr/glenda/mnt/home/lyssa/t $ > > > > Lets make a link on Linux, by passing the request through plan 9 and > back to Linux: > > > > lyssa@pibysix:/mnt/mnt/usr/glenda/mnt/home/lyssa/t $ ln -s > ../../../bin/ls another2 > > > > * The "ln" command makes a symlinkat(2) system call into the Linux > kernel. > > * The v9fs driver in the kernel fields the call and issues a Tsymlink > 9P2000.L message to my mounted adapter through a pipe. > > * My adapter receives that and translates it into a 9P Twalk to the > control file for the containing directory, Topens the file and issues a 9P > Twrite with the "symlink" > > command in it, which goes over the network to Plan 9 > > * exportfs running on Plan 9 receives the Twalk, Topen and Twrite, and > makes open(2) and pwrite(2) calls to the Plan 9 kernel. > > * devmnt in the Plan 9 kernel - I think... - issues the same Twalk, > Topen and Twrite requests over the network to my Linux 9P server. > > * My 9P server receives the Twrite command and issues a symlinkat(2) > system call. > > * The Linux server kernel makes the symbolic link. > > > > (there were some clunks and closes as well). > > > > lyssa@pibysix:/mnt/mnt/usr/glenda/mnt/home/lyssa/t $ ls -l > > total 24 > > lrwxrwxrwx 1 lyssa lyssa 15 Feb 13 18:00 another -> ../../../bin/ls > > lrwxrwxrwx 1 lyssa lyssa 15 Feb 13 18:03 another2 -> ../../../bin/ls > > -rw-r--r-- 1 lyssa lyssa 6 Feb 8 11:41 bar > > lrwxrwxrwx 1 lyssa lyssa 6 Feb 7 22:17 bin -> ../bin > > -rw-r--r-- 1 lyssa lyssa 6 Feb 10 15:06 foo > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 15:31 foop > > -rw-r--r-- 1 lyssa lyssa 1 Feb 9 18:33 foop2 > > drwxr-xr-x 2 lyssa lyssa 4096 Feb 7 00:54 foot > > lrwxrwxrwx 1 lyssa lyssa 3 Feb 7 01:06 hello -> foo > > lrwxrwxrwx 1 lyssa lyssa 5 Feb 11 02:08 hello6 -> hello > > -rw-r--r-- 1 lyssa lyssa 38 Feb 8 00:58 hi > > lrwxrwxrwx 1 lyssa lyssa 2 Feb 9 01:28 hi2 -> hi > > lrwxrwxrwx 1 lyssa lyssa 13 Feb 11 03:20 somenewlinkname -> > one/two/three > > lyssa@pibysix:/mnt/mnt/usr/glenda/mnt/home/lyssa/t $ > > > > So now Linux can mount file systems over 9P, and still see all the > nanosecond timestamps and other stuff: > > > > lyssa@pibysix:~/mnt/mnt/usr/glenda/mnt/home/lyssa/t $ stat foo > > File: foo > > Size: 6 Blocks: 8 IO Block: 4096 regular file > > Device: 36h/54d Inode: 265870 Links: 1 > > Access: (0644/-rw-r--r--) Uid: ( 1001/ lyssa) Gid: ( 1001/ lyssa) > > Access: 2025-02-10 15:06:02.460383798 +0000 > > Modify: 2025-02-10 15:06:02.470383712 +0000 > > Change: 2025-02-10 18:32:05.271025091 +0000 > > Birth: - > > lyssa@pibysix:~ > > > > (I suppose nanosecond resolution timestamps must be important to some > people...) > > My adapter is operating in a heterogeneous file system in this example, > where part of it has this extended behaviour, and part of it does not. > There's no mode switch or > > barriers - it just looks for the virtual files, and if they're not there > it does the standard thing. If I'd bound some other part of the Plan 9 > space over part of the the mounted > > Linux space before I exported it, the adapter would just fall back to > vanilla behaviour when file accesses are in that subtree. > > It's a work in progress. > > Linux is not actually my platform of choice, and symbolic links are not > exactly my spirit animal, but it's a familiar context for exploring the > ideas. > > > > I don't know what people think? > > This is about my third iteration of this idea. I'm not sure I'm done > with it yet. > > I wondering whether it would be better to have a single control file per > directory and some kind of sub-protocol going through it. It would possibly > be a less chatty > > alternative. But somehow not very appealing. > > I'm open to suggestions. > > 9fans / 9fans / see discussions + participants + delivery options > Permalink ------------------------------------------ 9fans: 9fans Permalink: https://9fans.topicbox.com/groups/9fans/T0f2c2342a05a3d6e-M7c26a395364c129143739c65 Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
