Re: [vserver] problem accessing NetApp Filer snapshot

From: Herbert Poetzl <herbert_at_13thfloor.at>
Date: Fri 07 Sep 2007 - 02:50:38 BST
Message-ID: <20070907015038.GE23963@MAIL.13thfloor.at>

On Thu, Sep 06, 2007 at 06:11:27PM -0700, Dallas Kashuba wrote:
> We have several vserver guests NFS mounting volumes being served from
> Network Appliance filers. The NFS mounting works as expected, other
> than access to the snapshots provided by the NetApp filesystem.

NFS tasgging is disabled, I presume?

> Under normal circumstances (non-vserver), you access the snapshot
> from anywhere along the filesystem by simply doing 'cd .snapshot'.
> Within there you will see a directory for each snapshot named
> something like hourly.0, nightly.0, or weekly.1 (etc), which contain
> copies of the files from those points in time. They work like any
> other directory aside from being read-only and being hidden from 'ls'
> output. Any user can access the snapshots for any part of the
> filesystem that user ordinarily has access to. No root access is
> required.
>
> Inside the vserver guests it does not work as expected, though.
> Attempting to 'cd .snapshot' never works at all unless BINARY_MOUNT
> is added to ccapabilities. This seems odd to me as there is no
> mounting taking place from what I understand, but the kernel seems to
> think there is.

there is a mount happening in this case,
because the filer provides the snapshot
as a different (subtree) export
(but it happens inside the kernel)

> With BINARY_MOUNT added, the root user is then able to access
> .snapshot in all cases. non-root users cannot, though. A non-root user
> CAN access a .snapshot portion of the filesystem after the root user
> has accessed it once previously, though. Here's an example...

and this works fine on the host system?
(I mean as non-root user on the host?)

> vserver03:/etc/vservers/patrick# vserver patrick enter
> patrick:/# su - testuser
> [patrick]$ whoami
> testuser
> [patrick]$ cd .snapshot
> -su: cd: .snapshot: Operation not permitted
> # (Note the "Operation not permitted" error)
>
> [patrick]$ logout
> # (back to root now)
>
> patrick:/# cd /home/testuser/.snapshot
> patrick:/# su - testuser
> [patrick]$ cd .snapshot
> # (after accessing it once as root, it's now accessible as the non-
> root user)
>
> [patrick]$ ls
> hourly.0 hourly.1 nightly.0 nightly.1 weekly.0 weekly.1
> [patrick]$ ls hourly.0
> ls: hourly.0: Operation not permitted
> # (access one more level down the filesystem is still not permitted)
>
> [patrick]$ logout
> patrick:/# cd /home/testuser/.snapshot/
> patrick:/home/testuser/.snapshot# ls -l
> total 32
> drwxr-x--x 7 testuser users 4096 Jul 3 10:53 hourly.0
> drwxr-x--x 7 testuser users 4096 Jul 3 10:53 hourly.1
> drwxr-x--x 7 testuser users 4096 Jul 3 10:53 nightly.0
> drwxr-x--x 7 testuser users 4096 Jul 3 10:53 nightly.1
> drwxr-x--x 7 testuser users 4096 Jul 3 10:53 weekly.0
> drwxr-x--x 7 testuser users 4096 Jul 3 10:53 weekly.1
>
> # (doing an ls -la as root accesses every directory below)
>
> patrick:/home/testuser/.snapshot# su - testuser
> [patrick]$ cd .snapshot/hourly.0
> [patrick]$ ls
> Maildir logs testdomain.com svn svntest
> [patrick]$ cd ../weekly.1
> [patrick]$ ls
> Maildir logs testdomain.com svn svntest
> [patrick]$ logout
>
> After the root user ran 'ls -la' inside .snapshot, the non-root user
> could then access all of the hourly.0, weekly.1 etc snapshot
> directories below.

this is most likely because the entries are
already in the dentry cache on the 'client'

> Does anyone have any clues about how to fix this?

> Ideally BINARY_MOUNT would not be needed at all, but

well, let's postpone this question ...

> it's ok as long as it works normally for non-root users.
>
> Any ideas are appreciated!

yeah, please provide the following debug info:

 - complete rpc and nfs(d) debug output for all
   cases, i.e. root/user on host/guest
 - Linux-VServer debug dmesg output

we know that the subtree checks (depending on
the nfs version) cause some issues, and I think
we can fix them with sufficient data ...

TIA,
Herbert

> Thanks!
> Dallas
>
>
>
Received on Fri Sep 7 02:50:48 2007

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