Re: Adding mount option to kernel for NFS filesystem

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Wed, 2009-04-29 at 17:16 +0200, Gertjan Oude Lohuis wrote:
> Hi guys,
> 
> For fun and learning purposes I'm trying to add an mountflag for 
> NFS-mounts to the kernel and mount. The flag's semantics are identical 
> to ac/noac: 'flag' is default but has no special meaning, 'noflag' 
> triggers a certain action.
> 
> I have a small question about adding the flag to 
> include/linux/nfs_mount.h. Since NFS_MOUNT_FLAGMASK is defined as 
> 0xFFFF, and all bits up until 0xFFFF are occupied by existing 
> NFS_MOUNT-flags, how could I add my own flag?
> Would it be ok to define NFS_MOUNT_FLAGMASK as 0xFFFFF and my own flag 
> as 0x10000? Or will this have other side effects? It seems to be working 
> though ;-).
> How would this be done if a real flag should be added by kernel maintainers?

The policy is that we don't add any more flags or features to the legacy
binary mount interface. NFS_MOUNT_FLAGMASK is there to enforce that
rule, so changing it is not acceptable.

All new mount features should be added using the text-based mount
interface (see nfs_parse_mount_options()), which is supported by recent
versions of the mount.nfs program in the nfs-utils package.

Cheers
  Trond