Re: [coLinux-users] unionfs in colinux?

[Henry N. <Hen...@Ar...>]

Hello Marwan,

Marwan Al-Sabbagh wrote:
> On Thu, Apr 3, 2008 at 6:43 PM, David Kaufman <da...@gi...> wrote:
>> Hi,
>>
>> I'd like to use unionfs in colinux:
>> http://www.fsl.cs.sunysb.edu/project-unionfs.html
>>
>> My goal is to have several colinux instances sharing a large read-only
>> filesystem (like the OS images that ship with colinux) and saving their
>> local changes to smaller writable local "unioned" filesystems.  This would
>> help me to repeatedly test-install large, complicated software packages
>> that we develop (such as http://krang.sf.net), with the ability to quickly
>> roll back the O/S to its pristine state and re-do as many times as needed,
>> and also to make it easy to identify and isolate all changes made to the
>> underlying distro afterwards (by examining the writable directory mounted).
>>
>> I read that unionfs was "baked in" to the linux kernel since 2.6.14 and
>> also see that it is supported by my distro (debian etch) so I was
>> disappointed when:
>>
>>  mount -t unionfs -o dirs=/Fruits:/Vegetables none /mnt/healthy
>>
>> complained that:
>>
>>  unknown file system unionfs
>>
>> Is unionfs not baked into the colinux kernel, too?  Am I doing something
>> wrong (or not doing something else right?)  Do I need to get the source,
>> compile and load the kernel module for colinux?  I've never done that
>> before, but for this I'd be anxious to give it a try!
>>
>> I'm running a recent 0.8.0 snapshot (at the moment) but would be willing to
>> up-, down-, or side-grade to get unionfs running!
>>
>> Thanks!
>>
>> -dave
>>
> 
> Dear David,
>   Unionfs is not in the default Linux kernel yet but should be in the
> future, this Quote is taken from http://en.wikipedia.org/wiki/UnionFS
> 
>   "As of January 2007, Unionfs 2.0 has been included into Andrew
> Morton's Linux -mm tree, thus slated for eventual inclusion in the
> Linux kernel mainline source tree."
> 
>   I've patched and compiled unionfs support into the colinux kernel,
> and it works great. As Henry mentioned there are no conflicts. I
> compiled it using coLinux-0.7.2 on debian 4 Etch. But the process
> pretty much applies to whichever distro and coLinux versions. I wrote
> a bash script that does the whole thing for you, as follows:
> 
>   * download colinux source, unionfs source, linux kernel source
>   * patch kernel with colinux patch and unionfs patch
>   * configure kernel for unionfs
>   * compile the kernel image and modules
> 
>   The script isn't too long about 60 lines, I've also tried to make it
> structured and readable. So you should be able to easily see what it's
> doing, and modify it for other versions or purposes. You can download
> the script at http://marwan.tv/build-unionfs-kernel.sh
> 
>   Two additional notes. Run the script as root or sudo, and run the
> following before running the scripts to install the packages needed to
> compile the Linux kernel:
> 
> apt-get install build-essential gettext bison flex automake autoconf unzip bzip2
> 
>   Best of luck, and I hope you find the script and this post helpful.
> 
> Marwan Al-Sabbagh

We have tried the module on Debian 4. We have build coLinux kernel
2.6.22.18 with unionfs patch 2.6.22.19. But it crashes the Kernel. The
minor differ version from .18 to .19 versions should not the problem.

David Kaufman wrote to me offlist:
>  sudo su -
>  modprobe unionfs
>  mkdir fruits vegies healthy
>  touch fruits/apple vegies/carrot
>  echo "I am a fruit" > fruits/tomato
>  echo "I am a vegetable" > vegies/tomato
>  mount -t unionfs -o dirs=/root/fruits:/root/vegies \
>    none /root/healthy
>  dir healthy        # works!
>  cat healthy/apple  # doesn't crash
>  cat healthy/tomato # should print: "I am a fruit"
>                     # (but crashes colinux instead) :-) 

I have replaced the "/root" with "/tmp" in the steps and have the same
result as David.

BUG at .../devel-gcc412/linux-2.6.22.18-source/fs/unionfs/fanout.h:313"

static inline void verify_locked(struct dentry *d)
{
        BUG_ON(!d);
        BUG_ON(!mutex_is_locked(&UNIONFS_D(d)->lock));  <=== failed
}

Have changed the lines above into WARN + BUG to have the caller tree.

static inline void verify_locked(struct dentry *d)
{
        BUG_ON(!d);

        //BUG_ON(!mutex_is_locked(&UNIONFS_D(d)->lock));
        if (WARN_ON(!mutex_is_locked(&UNIONFS_D(d)->lock)))
                BUG();
}

------- Now, can see the callers: -----------------------
Registering unionfs 2.3.2 (for 2.6.22.19) on .18
WARNING: at
/home/hn/colinux/build/devel-gcc412/linux-2.6.22.18-source/fs/unionf
:315 verify_locked()
 [<c0103b7a>] show_trace_log_lvl+0x1a/0x30
 [<c0103cb2>] show_trace+0x12/0x20
 [<c0104ae5>] dump_stack+0x15/0x20
 [<c884255c>] unionfs_file_revalidate+0x63c/0xfc0 [unionfs]
 [<c884545e>] unionfs_readpage+0x3e/0x1d0 [unionfs]
 [<c0144d23>] __do_page_cache_readahead+0x1e3/0x2b0
 [<c0144e52>] blockable_page_cache_readahead+0x62/0xc0
 [<c01450a9>] page_cache_readahead+0x149/0x1f0
 [<c013ed70>] do_generic_mapping_read+0x4f0/0x5a0
 [<c0140c92>] generic_file_aio_read+0x122/0x1c0
 [<c015de1f>] do_sync_read+0xcf/0x110
 [<c015e705>] vfs_read+0xb5/0x140
 [<c015eaed>] sys_read+0x3d/0x70
 [<c01028f2>] syscall_call+0x7/0xb
 =======================
colinux: Linux VM terminated
colinux: BUG at
.../devel-gcc412/linux-2.6.22.18-source/fs/unionfs/fanout.h:316
console: Monitor1492: Detached
===============================================================

I can not see any coLinux related things there. Perhaps some should
fillout a bugreport on unionfs?

My changed code you can see from versions message "on .18"
http://www.henrynestler.com/colinux/testing/devel-0.8.0/20080403-unionfs/bug-fanout.h-313/

Marwan, what patchfile you have used? What version of unionfs?

-- 
Henry N.