Adding mount option to kernel for NFS filesystem

Adding mount option to kernel for NFS filesystem

[Gertjan Oude Lohuis]

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?

I guess another option would be to create a new entry in the
nfs_mount_data struct and treat it as an option (rsize-, wsize-,
timeo-alike), but I'd like to do keep it the same as other flags.

Please advice! ;-)
Thanks in advance for your time.

Sincerely,
Gertjan

Re: Adding mount option to kernel for NFS filesystem

[Jeff Layton]

On Wed, 29 Apr 2009 19:03:06 +0200
Gertjan Oude Lohuis <gertjan-yZ1RIXqxfwWWrUy98/Atqw@public.gmane.org> 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?
> 
> I guess another option would be to create a new entry in the
> nfs_mount_data struct and treat it as an option (rsize-, wsize-,
> timeo-alike), but I'd like to do keep it the same as other flags.
> 
> Please advice! ;-)
> Thanks in advance for your time.
> 
> Sincerely,
> Gertjan
> 

It's probably better to post questions like this to
linux-nfs-u79uwXL29TaiAVqoAR/hOA@public.gmane.org cc'ing that on the response...

Newer kernels and mount.nfs progs use text-based mount options by
default. My suggestion would be to avoid worrying about the legacy
mount option code and to just make the new option work with the text
based ones only.

Cheers,
-- 
Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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Adding mount option to kernel for NFS filesystem

[Gertjan Oude Lohuis]

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?

I guess another option would be to create a new entry in the 
nfs_mount_data struct and treat it as an option (rsize-, wsize-, 
timeo-alike), but I'd like to do keep it the same as other flags.

Please advice! ;-)
Thanks in advance for your time.

Sincerely,
Gertjan

Re: Adding mount option to kernel for NFS filesystem

[Trond Myklebust]

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