Re: [uml-devel] filemap feature 2.4.22-5um

["Steve Schmidtke" <steve_schmidtke@hotmail.com>]

Doug Dumitru wrote:
>A couple of questions.  I noticed that you are not mapping /proc/mm.
[...]
>This looks like one per virtual process (minus threads).  Am I reading this 
>right.

yes. The discussion for a previous patch considered a "mm" table to hold a 
pool of /proc/mm files to handle one fd per process.  One side effect of 
this would place a hard limit on the number of processes in the UML: the 
number of /proc/mm files opened.  I'm not sure what side effects re-using 
/proc/mm files would have, either.  I should have mentioned TT/SKAS issues, 
but it slipped my mind (I only use TT mode). So to use skas in a chroot, 
you'll still have to mount /proc/mm in there.  Hopefully Jeff has a fix for 
/proc/mm in the works.

>On virtuals that I run, I tend to only see a single "vm" file opened:

yup. Things have changed since I looked at it for the last filemap patch 
*sigh*.  It used to be 1 file for every 256M of memory, but now, it is just 
one big happy file, so in SKAS mode you should need only one vm file entry.  
In TT mode there are a few more files required, but the max now seems to be 
3 or 4 entries.

>Is there any reason the tun/tap networking wouldn't work with this layout 
>by pre-opening /dev/net/tun.

Possibly, but you will have to check out the "TUN/TAP with a preconfigured 
tap device" section of the virtual networking howto as the uml_net helper 
won't pick up the filemapped fd for /dev/net/tun inside a chroot (nor will 
it likely have ifconfig or route binaries available).   Let me know if you 
get this to work.

Steve Schmidtke

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