A question in the context of independent pquota

A question in the context of independent pquota

[Chandra Seetharaman]

Hi All,

Few days back I posted a patchset to allow pquota and gquota to be used
together. I have a question in that context.

In order for the user space to get the stats for pguota and gquota
together (quotactl command Q_XGETQSTAT), I need to add a field to
fs_quota_stat. So, I have to change the version number.

But, the version number is only set in the kernel and not checked. Which
means the kernel cannot know what size of the fs_quota_stat data
structure the user space has provided in order to decide if the kernel
can copy the newer (bigger) data structure to the user space or not.

One option I see is to add a new command to the ioctl.

Is there any other options ? ( or am I totally missing it :) ?

Thanks

Chandra






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Re: A question in the context of independent pquota

[Christoph Hellwig]

Hi Chandra,

I don't think there is an easy way to add a field there.  Please
just add a new Q_XGETQSTAT_2 call that takes the new, larger structure.

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Re: A question in the context of independent pquota

[Chandra Seetharaman]

On Tue, 2011-10-25 at 07:54 -0400, Christoph Hellwig wrote:
> Hi Chandra,
> 
> I don't think there is an easy way to add a field there.  Please
> just add a new Q_XGETQSTAT_2 call that takes the new, larger structure.

Christoph,

I came up with couple of ideas.

- Add a new version FS_QSTAT_VERSION2 (with a value of 2) that uses
  the newer fs_quota_stat
- Start using qs_version in the user space code, with the bigger 
  fs_quota_stat
- Define a macro to check if the given version is a valid one.
- In xfs_qm_scall_getqstat()(kernel), copy in the newer fs_quota_stat
  structure from user space.
  If copy in succeeded, check qs_version. 
     If valid, use the structure relevant to the version.
     If invalid, use structure for the version FS_QSTAT_VERSION.
  If copy in failed,
     use structure for the version FS_QSTAT_VERSION.

I think it should work with the current user space code.

Let me know what you think of it.

Thanks & Regards,

Chandra
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