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-Mf1907334a2888ce3b233343c Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
