nfsroot mount options

nfsroot mount options

[Jim Rees]

If I boot diskless with nfsroot, why is the root file system mounted
readonly?  This makes sense for a file system on disk, since it may have to
be checked before remounting rw, but I don't see why this is needed for
nfsroot.

Also, Documentation/filesystems/nfs/nfsroot.txt says that only nfs options
can be given on the kernel nfsroot option, but I've seen a claim that you
can also put "rw" here.  Are other generic options possible?  How about the
nfs options that aren't listed in the doc?  Should the doc be updated?

Re: nfsroot mount options

[Chuck Lever]

On Dec 1, 2010, at 7:18 PM, Jim Rees wrote:

> If I boot diskless with nfsroot, why is the root file system mounted
> readonly?  This makes sense for a file system on disk, since it may have to
> be checked before remounting rw, but I don't see why this is needed for
> nfsroot.
> 
> Also, Documentation/filesystems/nfs/nfsroot.txt says that only nfs options
> can be given on the kernel nfsroot option, but I've seen a claim that you
> can also put "rw" here.  Are other generic options possible?  How about the
> nfs options that aren't listed in the doc?  Should the doc be updated?

What kernel version are you looking at?  I think 2.6.37-rc has some nfsroot updates that allow all NFS options to be used.

Not sure about the generic mount options.  Why not just try them and see?

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com

Re: nfsroot mount options

[Jim Rees]

Chuck Lever wrote:

  On Dec 1, 2010, at 7:18 PM, Jim Rees wrote:
  
  > If I boot diskless with nfsroot, why is the root file system mounted
  > readonly?  This makes sense for a file system on disk, since it may have to
  > be checked before remounting rw, but I don't see why this is needed for
  > nfsroot.
  > 
  > Also, Documentation/filesystems/nfs/nfsroot.txt says that only nfs options
  > can be given on the kernel nfsroot option, but I've seen a claim that you
  > can also put "rw" here.  Are other generic options possible?  How about the
  > nfs options that aren't listed in the doc?  Should the doc be updated?
  
  What kernel version are you looking at?  I think 2.6.37-rc has some
  nfsroot updates that allow all NFS options to be used.
  
  Not sure about the generic mount options.  Why not just try them and see?

This is Ubuntu lucid, so 2.6.32.  I'm less concerned about the documentation
defect than the question about the default being readonly.  Is there any
good reason other than to match the behavior of non-nfs root?

I ask because there has been a bug in ubuntu for a long time (a couple of
releases) that prevents nfsroot from working.  Their mountall is broken and
can't remount an nfs root rw.  They need to fix this obviously, but it got
me to wondering why the remount should be needed at all.

The bug report is here:
https://bugs.launchpad.net/ubuntu/+source/mountall/+bug/537133

Re: nfsroot mount options

[Chuck Lever]

On Dec 2, 2010, at 12:09 PM, Jim Rees wrote:

> Chuck Lever wrote:
> 
>  On Dec 1, 2010, at 7:18 PM, Jim Rees wrote:
> 
>> If I boot diskless with nfsroot, why is the root file system mounted
>> readonly?  This makes sense for a file system on disk, since it may have to
>> be checked before remounting rw, but I don't see why this is needed for
>> nfsroot.
>> 
>> Also, Documentation/filesystems/nfs/nfsroot.txt says that only nfs options
>> can be given on the kernel nfsroot option, but I've seen a claim that you
>> can also put "rw" here.  Are other generic options possible?  How about the
>> nfs options that aren't listed in the doc?  Should the doc be updated?
> 
>  What kernel version are you looking at?  I think 2.6.37-rc has some
>  nfsroot updates that allow all NFS options to be used.
> 
>  Not sure about the generic mount options.  Why not just try them and see?
> 
> This is Ubuntu lucid, so 2.6.32.  I'm less concerned about the documentation
> defect than the question about the default being readonly.  Is there any
> good reason other than to match the behavior of non-nfs root?
> 
> I ask because there has been a bug in ubuntu for a long time (a couple of
> releases) that prevents nfsroot from working.  Their mountall is broken and
> can't remount an nfs root rw.  They need to fix this obviously, but it got
> me to wondering why the remount should be needed at all.
> 
> The bug report is here:
> https://bugs.launchpad.net/ubuntu/+source/mountall/+bug/537133

OK, Ubuntu doesn't use NFSROOT (the kernel's implementation), it actually does a real mount in user space.  So all the normal NFS and generic mount options ought to work.

However, I worked on the kernel's implementation recently, not Ubuntu's "nfsroot", so that's as far as my expertise goes.

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com

Re: nfsroot mount options

[Jim Rees]

Chuck Lever wrote:

  OK, Ubuntu doesn't use NFSROOT (the kernel's implementation), it actually
  does a real mount in user space.  So all the normal NFS and generic mount
  options ought to work.

I didn't realize that.  I wonder why, especially since it doesn't work.  So
they pack a copy of nfs-utils in their initrd?  And I could maybe use v4 as
the root?

But if that's the case then I'm getting off topic for this list.  Thanks for
your help.