[PATCH] umount: unconditionally delete loopback device

Florian Fainelli florian at alphacore.org
Mon Apr 16 08:43:22 UTC 2012


Le 04/16/12 03:17, Denys Vlasenko a écrit :
> On Friday 06 April 2012 10:41, Florian Fainelli wrote:
>> I have been recently caught by an interesting issue, illustrated by the
>> following use case:
>>
>> "foo" is a cramfs filesystem file which might help illustrate the issue
>> below:
>>
>> 1) loopback mount "foo" to mount point /bar
>> 2) umount /bar
>> 3) append new files and re-generate the "foo" cramfs image
>> 4) loopback mount "foo" to mount point /bar again
>> 5) the contents of /bar are the same as in 1) and not 3)
>>
>> the reason for this is because busybox has not deleted the "foo"<->
>> loopback device mapping, so when we attempt to mount again "foo", the
>> mapping is already there, so the loopback device is not deleted then
>> re-created.
>>
>> util-linux' umount unconditionnaly deletes the loop device upon umount
> It does that? Really? Which version of util-linux did you test?
>
Yes it does, util-linux on my system is at 2.19.1. Ralf suggested 
off-list to me that util-linux might do this automatically when 
/etc/mtab is not a symlink to /proc/mounts.


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