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Re: [PATCH v8 4/5] xfs: Add proper versioning support to fs_quota_stat

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH v8 4/5] xfs: Add proper versioning support to fs_quota_stat
From: Chandra Seetharaman <sekharan@xxxxxxxxxx>
Date: Fri, 24 May 2013 17:17:22 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130517051001.GP24635@dastard>
Organization: IBM
References: <1368220889-25188-1-git-send-email-sekharan@xxxxxxxxxx> <1368220889-25188-5-git-send-email-sekharan@xxxxxxxxxx> <20130517051001.GP24635@dastard>
Reply-to: sekharan@xxxxxxxxxx
On Fri, 2013-05-17 at 15:10 +1000, Dave Chinner wrote:
> On Fri, May 10, 2013 at 04:21:28PM -0500, Chandra Seetharaman wrote:
> > Added appropriate pads and code for backward compatibility.
> > 
> > Copied over the old version as it is different from the newer padded
> > version.
> > 
> > New callers of the system call have to just set the version of the data
> > structure being passed, and kernel will fill as much data as requested.
> > 
> > Signed-off-by: Chandra Seetharaman <sekharan@xxxxxxxxxx>
> 
> This needs to be cc'd to Steve Whitehouse so he's aware that we are
> changing the quota interface...

Will do.

> 
> > ---
> >  fs/gfs2/quota.c                |    3 ---
> >  fs/quota/quota.c               |   40 
> > ++++++++++++++++++++++++++++++++++++++--
> >  fs/xfs/xfs_qm_syscalls.c       |    4 ----
> >  include/uapi/linux/dqblk_xfs.h |   38 
> > ++++++++++++++++++++++++++++++++++++--
> >  4 files changed, 74 insertions(+), 11 deletions(-)
> > 
> > diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> > index c7c840e..ca0dccd 100644
> > --- a/fs/gfs2/quota.c
> > +++ b/fs/gfs2/quota.c
> > @@ -1443,9 +1443,6 @@ static int gfs2_quota_get_xstate(struct super_block 
> > *sb,
> >  {
> >     struct gfs2_sbd *sdp = sb->s_fs_info;
> >  
> > -   memset(fqs, 0, sizeof(struct fs_quota_stat));
> > -   fqs->qs_version = FS_QSTAT_VERSION;
> > -
> >     switch (sdp->sd_args.ar_quota) {
> >     case GFS2_QUOTA_ON:
> >             fqs->qs_flags |= (FS_QUOTA_UDQ_ENFD | FS_QUOTA_GDQ_ENFD);
> > diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> > index c7314f1..510464e 100644
> > --- a/fs/quota/quota.c
> > +++ b/fs/quota/quota.c
> > @@ -207,12 +207,48 @@ 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 *cp = &fqs;
> 
> What's "cp" mean? Wouldn't fqsp be a better name? And initialise it
> just before it gets used makes more sense, too.
> 
will do

> >  
> >     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;
> > +           cp = &fqs_v1;
> > +   }
> 
> Missing a break on the last case there.
will add.

> 
> > +
> >     ret = sb->s_qcop->get_xstate(sb, &fqs);
> > -   if (!ret && copy_to_user(addr, &fqs, sizeof(fqs)))
> > +   if (ret)
> > +           return ret;
> > +
> > +   if (fqs.qs_version == FS_QSTAT_VERSION) {
> > +           fqs_v1.qs_version = fqs.qs_version;
> > +           fqs_v1.qs_flags = fqs.qs_flags;
> > +           fqs_v1.qs_pad = 0;
> > +           fqs_v1.qs_uquota = fqs.qs_uquota;
> > +           fqs_v1.qs_gquota = fqs.qs_gquota;
> > +           fqs_v1.qs_incoredqs = fqs.qs_incoredqs;
> > +           fqs_v1.qs_btimelimit = fqs.qs_btimelimit;
> > +           fqs_v1.qs_itimelimit = fqs.qs_itimelimit;
> > +           fqs_v1.qs_rtbtimelimit = fqs.qs_rtbtimelimit;
> > +           fqs_v1.qs_bwarnlimit = fqs.qs_bwarnlimit;
> > +           fqs_v1.qs_iwarnlimit = fqs.qs_iwarnlimit;
> 
>               fsqp = &fsq_v1;
>       } else {
>               fsqp = &fsq_v2;
>       }
> 
sure

> > +
> > +   if (copy_to_user(addr, &cp, size))
> >             return -EFAULT;
> >     return ret;
> >  }
> > diff --git a/include/uapi/linux/dqblk_xfs.h b/include/uapi/linux/dqblk_xfs.h
> > index f17e3bb..d9629c1 100644
> > --- a/include/uapi/linux/dqblk_xfs.h
> > +++ b/include/uapi/linux/dqblk_xfs.h
> > @@ -18,6 +18,7 @@
> >  #define _LINUX_DQBLK_XFS_H
> >  
> >  #include <linux/types.h>
> > +#include <linux/stddef.h>
> 
> Really? What's new that requires this include?

will fix.

> 
> >  
> >  /*
> >   * Disk quota - quotactl(2) commands for the XFS Quota Manager (XQM).
> > @@ -137,8 +138,12 @@ typedef struct fs_disk_quota {
> >   * Provides a centralized way to get meta information about the quota 
> > subsystem.
> >   * eg. space taken up for user and group quotas, number of dquots currently
> >   * incore.
> > + * User space caller should set qs_version to the appropriate version
> > + * of the fs_quota_stat data structure they are providing. Not providing
> > + * a version will be treated as FS_QSTAT_VERSION.
> >   */
> >  #define FS_QSTAT_VERSION   1       /* fs_quota_stat.qs_version */
> > +#define FS_QSTAT_VERSION_2 2       /* new field qs_pquota */
> >  
> >  /*
> >   * Some basic information about 'quota files'.
> > @@ -149,19 +154,48 @@ typedef struct fs_qfilestat {
> >     __u32           qfs_nextents;   /* number of extents */
> >  } fs_qfilestat_t;
> >  
> > +typedef struct fs_quota_stat_v1 {
> 
> Kill the typedef. Add a comment stating that this structure is
> likely to have compatibility problems across architectures due to
> implicit padding and offset alignment in the structure definition
> and that the v2 structure should be used if these problems are being
> seen.

will do
> 
> > +   __s8            qs_version;     /* version number for future changes */
> > +   __u16           qs_flags;       /* FS_QUOTA_{U,P,G}DQ_{ACCT,ENFD} */
> > +   __u8            qs_pad;         /* unused */
> > +   fs_qfilestat_t  qs_uquota;      /* user quota storage information */
> > +   fs_qfilestat_t  qs_gquota;      /* group quota storage information */
> > +   __u32           qs_incoredqs;   /* number of dquots incore */
> > +   __s32           qs_btimelimit;  /* limit for blks timer */      
> > +   __s32           qs_itimelimit;  /* limit for inodes timer */    
> > +   __s32           qs_rtbtimelimit;/* limit for rt blks timer */   
> > +   __u16           qs_bwarnlimit;  /* limit for num warnings */
> > +   __u16           qs_iwarnlimit;  /* limit for num warnings */
> > +} fs_quota_stat_v1_t;
> > +
> >  typedef struct fs_quota_stat {
> 
> Kill the typedef.
> 
> >     __s8            qs_version;     /* version number for future changes */
> > +   __u8            qs_pad1;        /* unused */
> >     __u16           qs_flags;       /* FS_QUOTA_{U,P,G}DQ_{ACCT,ENFD} */
> > -   __s8            qs_pad;         /* unused */
> > +   __u8            qs_pad2[4];     /* unused */
> >     fs_qfilestat_t  qs_uquota;      /* user quota storage information */
> >     fs_qfilestat_t  qs_gquota;      /* group quota storage information */
> > -#define qs_pquota  qs_gquota
> >     __u32           qs_incoredqs;   /* number of dquots incore */
> >     __s32           qs_btimelimit;  /* limit for blks timer */      
> >     __s32           qs_itimelimit;  /* limit for inodes timer */    
> >     __s32           qs_rtbtimelimit;/* limit for rt blks timer */   
> >     __u16           qs_bwarnlimit;  /* limit for num warnings */
> >     __u16           qs_iwarnlimit;  /* limit for num warnings */
> > +   __u8            qs_pad3[4];     /* unused */
> > +   fs_qfilestat_t  qs_pquota;      /* project quota storage information */
> > +   /* End of Data structure for FS_QSTAT_VERSION_2 */
> 
> No need for that comment.
> 
> >  } fs_quota_stat_t;
> 
> Use pahole on the built object file to determine if the end ofthe
> structure is 64 bit aligned. If it isn't, please pad it to 64 bit
> alignment.

sure.
> 
> Um. fs_qfilestat_t is { u64, u64, u32 }, and so there's going to be
> alignment problems with that. We need a fs_qfilestat_v1 definition
> and add padding to fs_qfilestat_t so that it is 64 bit aligned.....
> 

will do.

> 
> >  
> > +/*
> > + * Since Version 1 did not have padding at appropriate places,
> > + * a new data structure has been defined for the older version to
> > + * provide backward compatibility.
> > + * Future extentions of this data structure won't require new
> > + * data structure definitions as the current one can be extended
> > + * with the logic and padding in place now.
> > + */
> > +#define FS_QSTAT_V1_SIZE   (sizeof(struct fs_quota_stat_v1))
> > +#define FS_QSTAT_V2_SIZE   (offsetof(struct fs_quota_stat, qs_pquota) + \
> > +                                   sizeof(fs_qfilestat_t))
> 
> Just use sizeof(struct fs_quota_stat) as the size. Indeed, for

My thinking w.r.t not making it sizeof (fs_quota_stat) is ...future
changes doesn't have to touch the macro definitions of earlier versions,
they can define a new macro just by copying the last V?_SIZE macro and
changing the last field name.

> future enhancements, maybe we should add 64 bytes of empty space at
> the end of the structure....

Since this version is fully backward compatible, I didn't think a future
pad was needed. Do you want me to add ?
> Cheers,
> 
> Dave.


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