It would be preferable to do a mount --bind --make-private in one atomic action [ASCII art this time]

* It would be preferable to do a mount --bind --make-private in one atomic action [ASCII art this time]
@ 2011-11-23 17:36 Anders Blomdell
  0 siblings, 0 replies; only message in thread
From: Anders Blomdell @ 2011-11-23 17:36 UTC (permalink / raw)
  To: Alexander Viro, linux-fsdevel, linux-kernel

Sorry about previous posts used character set!

The rationale is the race problems I recently found with pam_namspace 
(see https://bugzilla.redhat.com/show_bug.cgi?id=755216). The following 
small script and it's output shows what pam_namespace essentially does 
does, and the problems that might occur; assume that /work is 
automounted, then the following really confuses things:

(
echo '# Empty work'
findmnt -a | cut -c1-30 | grep work
echo '# First primary mount on work'
ls -ld /work/Fedora-16/.
findmnt -a | cut -c1-30 | grep work
unshare --mount -- /bin/sh -c "(
     mount --bind /work /work ;
     mount --make-private /work ;
     mount --bind /tmp /work ;
     echo '# Detached mount of work' ;
     findmnt -a | cut -c1-30 | grep work ;
     sleep 5 ;
     echo '# Before detached unmount of private work' ;
     findmnt -a | cut -c1-30 | grep work;
     umount /work ;
     echo '# Before detached unmount of bound work' ;
     findmnt -a | cut -c1-30 | grep work;
     echo '# Weird detached automount behaviour' ;
     ls -ld /work/Fedora-15/. ;
     umount /work ;
     echo '# Detached unmount') &"
sleep 1
echo '# Second primary mount on work'
ls -ld /work/Fedora-15/.
findmnt -a | cut -c1-30 | grep work
echo '# First primary mount on work no longer accessible'
ls -ld /work/Fedora-16/.
sleep 10
echo '# And the final remaining cruft'
findmnt -a | cut -c1-30 | grep work
)

Which gives the following output (no wonder I had problems understanding 
what went wrong with my machines :-():

-- 
Anders Blomdell                  Email: anders.blomdell@control.lth.se
Department of Automatic Control
Lund University                  Phone:    +46 46 222 4625
P.O. Box 118                     Fax:      +46 46 138118
SE-221 00 Lund, Sweden

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