Re: [PATCH v10 10/11] quota: Add proper versioning support to fs_quota_stat

[Chandra Seetharaman <sekharan@us.ibm.com>]

On Wed, 2013-07-10 at 18:26 +0200, Jan Kara wrote:
> On Wed 10-07-13 10:55:38, Ben Myers wrote:
> > Hey Chandra,

<snip>

> > > diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> > > index c7314f1..ae6526e 100644
> > > --- a/fs/quota/quota.c
> > > +++ b/fs/quota/quota.c
> > > @@ -207,12 +207,57 @@ static int quota_setxstate(struct super_block *sb, int cmd, void __user *addr)
> > >  static int quota_getxstate(struct super_block *sb, void __user *addr)
> > >  {
> > >  	struct fs_quota_stat fqs;
> > > -	int ret;
> > > +	struct fs_quota_stat_v1 fqs_v1;
> > > +	int ret, size;
> > > +	void *fqsp;
> > >  
> > >  	if (!sb->s_qcop->get_xstate)
> > >  		return -ENOSYS;
> > > +
> > > +	memset(&fqs, 0, sizeof(struct fs_quota_stat));
> > > +	if (copy_from_user(&fqs, addr, 1)) /* just get the version */
> > > +		return -EFAULT;
> > > +
> > > +	switch (fqs.qs_version) {
> > > +	case FS_QSTAT_VERSION_2:
> > > +		size = FS_QSTAT_V2_SIZE;
> > > +		break;
> > > +	default:
> > > +		fqs.qs_version = FS_QSTAT_VERSION;
> > > +		/* fallthrough */
> > > +	case FS_QSTAT_VERSION:
> > > +		size = FS_QSTAT_V1_SIZE;
> > > +		break;
> > > +	}
>   Guys, you cannot really do this. If anyone is using getxstate() with
> uninitialized buffer (which is fine so far), you cannot suddently start to
> rely on the contents of qs_version field. That's ABI (and even API)
> breakage.

Agree, it is a API breakage.

Will fix it by adding a new quotactl value as you suggest. 
Does 

#define Q_XGETQSTAT2     XQM_CMD(8)

sound good ?
> 
> Unless I'm missing something, the only clean way is to use new quotactl
> value for the interface with version field used for input as well.
> 
> 								Honza
> 


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