[Devel] Re: [PATCH 0/9] Multiple devpts instances

[Serge E. Hallyn]

Quoting sukadev at linux.vnet.ibm.com (sukadev at linux.vnet.ibm.com):
> 
> Enable multiple instances of devpts filesystem so each container can allocate
> ptys independently.

Hey Suka,

I was playing with this a bit last night, trying to make it oops, i.e.
create an sshd in a child ptsns ssh to it, and umount -l /dev/pts out
from under me.  Etc.  Ran ltp.

All seemed fine.

Tested-by: Serge Hallyn <serue at us.ibm.com>
Acked-by: Serge Hallyn <serue at us.ibm.com>

thanks,
-serge

> User interface:
> 
> 	Since supporting multiple mounts of devpts can break user-space, this
> 	feature is enabled only if:
> 
> 		- CONFIG_DEVPTS_MULTIPLE_INSTANCES=y (new config token), and
> 		- new mount option, -o newinstance is specified
> 
> 	If CONFIG_DEVPTS_MULTIPLE_INSTANCES=n, there should be no change in
> 	behavior.
> 
> 	See [PATCH 9/9] - Documentation/filesystems/devpts.txt for detailed
> 	usage/compatibility information.
> 
> 		[PATCH 1/9] Remove devpts_root global
> 		[PATCH 2/9] Per-mount allocated_ptys
> 		[PATCH 3/9] Per-mount 'config' object
> 		[PATCH 4/9] Extract option parsing to new function
> 		[PATCH 5/9] Add DEVPTS_MULTIPLE_INSTANCES config token
> 		[PATCH 6/9] Define mknod_ptmx()
> 		[PATCH 7/9] Define get_init_pts_sb()
> 		[PATCH 8/9] Enable multiple instances of devpts
> 		[PATCH 9/9] Document usage of multiple-instances of devpts
> 	
> Implementation notes:
> 
> 	1. To enable multiple mounts of /dev/pts, (most) devpts interfaces
> 	   need to know which instance of devpts is being accessed. This
> 	   patchset uses the 'struct inode' or 'struct tty_struct' of the
> 	   device being accessed to identify the appropriate devpts instance.
> 	   Hence the need for the /dev/pts/ptmx bind-mount.
> 
> 	2. Mount options must be parsed twice during mount (once to determine
> 	   the mode of mount (single/multi-instance) and once to actually
> 	   save the options. There does not seem to be an easy way to parse
> 	   once and reuse (See 'safe_process_mount_opts()' in [PATCH 9/10])
> 
> 
> Changelog [v5]:
> 	- Merge all option-parsing (previously in patches 6,7) into patch 6.
> 	- Bugfixes (see changelog in patches 6 and 8)
> 	- Replace get_sb_ref() with devpts-specific get_init_pts_sb() (patch 7)
> 	- Minor update to devpts.txt documentation (patch 9)
> 
> 
> Changelog [v4]:
> 
> 	- Port to 2008-09-04 ttydev tree (and drop patches that were merged in)
> 	- Add DEVPTS_MULTIPLE_INSTANCES config token (patch 5) and move new
> 	  behavior under #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES. 
> 	- Create ptmx node even in initial mount 
> 	- Change default permissions of pts/ptmx node to 0000 (patch 6)
> 	- Cache ptmx dentry and use to update permissions of ptmx node on
> 	  remount so legacy mode can use the node with a simpler change to
> 	  /etc/fstab (patch 7)
> 	- Move get_sb_ref() helper code to separate patch (patch 8)
> 	- Add Documentation/filesystems/devpts.txt and describe usage info
> 	  in that file.
> 	  
> Changelog [v3]:
> 
> 	- Port to 2008-08-28 ttydev tree
> 	- Rename new mount options to 'ptmxmode' and 'newinstance'.
> 	- [Alan Cox] Use tty driver data to identify devpts (this is used to
> 	  cleanup get_node() in devpts_pty_kill()).
> 	- [H. Peter Anvin] get_node() cleanup in devpts (which was enabled by
> 	  the inode/tty parameter to devpts interfaces)
> 	- Bugfix in multi-mount mode (see Patch 11/11).
> 	- Executed pty tests in LTP (in both single-instance and multi-instance
> 	  mode)
> 	- Should be bisect-safe :-)
> 
> Changelog [v2]:
> 
> 	- New mount option '-o newmnt' added (patch 8/8)
> 	- Support both single-mount and multi-mount semantics (patch 8/8)
> 	- Automatically create ptmx node when devpts is mounted (patch 7/8)
> 	- Extract option parsing code to new function (patch 6/8)
> 	- Make 'config' params per-mount variables (patch 5/8)
> 	- Slightly re-ordered existing patches in set (patches 1/8, 2/8)
> 
> TODO:
> 	- Do we need a '-o ptmxuid' and '-o ptmxgid' options as well ?
> 	- Update mount(8) man page
> 	- (Sometime in future) Remove even initial kernel mount of devpts 
> 	- Any other good test suites to test this (besides LTP, sshd).
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