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Subject: Re: [RFC PATCH 1/4] vfs: report change attribute in statx for
 IS_I_VERSION inodes
From:   Jeff Layton <jlayton@redhat.com>
To:     JunChao Sun <sunjunchao2870@gmail.com>
Cc:     linux-fsdevel@vger.kernel.org, dhowells@redhat.com,
        lczerner@redhat.com, bxue@redhat.com, ceph-devel@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-afs@lists.infradead.org,
        linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
        linux-btrfs@vger.kernel.org
Date:   Wed, 10 Aug 2022 06:35:38 -0400
In-Reply-To: <CAHB1Nah5ttUCuUUdPZjb9n_1uDTh_-J_N6JaJiwY+oZj7atJeg@mail.gmail.com>
References: <20220805183543.274352-1-jlayton@kernel.org>
         <20220805183543.274352-2-jlayton@kernel.org>
         <CAHB1Nah5ttUCuUUdPZjb9n_1uDTh_-J_N6JaJiwY+oZj7atJeg@mail.gmail.com>
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On Wed, 2022-08-10 at 11:00 +0800, JunChao Sun wrote:
> On Sat, Aug 6, 2022 at 2:37 AM Jeff Layton <jlayton@kernel.org> wrote:
> >=20
> > From: Jeff Layton <jlayton@redhat.com>
> >=20
> > Claim one of the spare fields in struct statx to hold a 64-bit change
> > >=20
> > > attribute. When statx requests this attribute, do an
> > > inode_query_iversion and fill the result in the field.
>=20
> I guess, is it better to update the corresponding part of the man-pages..=
.?

Yes. If we end up accepting a patch like this, we'll need to update the
statx(2) manpage. We'll probably also want to add support for it to the
/bin/stat coreutils command as well.

At this point, I'm trying to put together some xfstests so we can ensure
that this feature doesn't regress (if we take it).

> >=20
> >=20
> > Also update the test-statx.c program to fetch the change attribute as
> > well.
> >=20
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/stat.c                 | 7 +++++++
> >  include/linux/stat.h      | 1 +
> >  include/uapi/linux/stat.h | 3 ++-
> >  samples/vfs/test-statx.c  | 4 +++-
> >  4 files changed, 13 insertions(+), 2 deletions(-)
> >=20
> > diff --git a/fs/stat.c b/fs/stat.c
> > index 9ced8860e0f3..976e0a59ab23 100644
> > --- a/fs/stat.c
> > +++ b/fs/stat.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/syscalls.h>
> >  #include <linux/pagemap.h>
> >  #include <linux/compat.h>
> > +#include <linux/iversion.h>
> >=20
> >  #include <linux/uaccess.h>
> >  #include <asm/unistd.h>
> > @@ -118,6 +119,11 @@ int vfs_getattr_nosec(const struct path *path, str=
uct kstat *stat,
> >         stat->attributes_mask |=3D (STATX_ATTR_AUTOMOUNT |
> >                                   STATX_ATTR_DAX);
> >=20
> > +       if ((request_mask & STATX_CHGATTR) && IS_I_VERSION(inode)) {
> > +               stat->result_mask |=3D STATX_CHGATTR;
> > +               stat->chgattr =3D inode_query_iversion(inode);
> > +       }
> > +
> >         mnt_userns =3D mnt_user_ns(path->mnt);
> >         if (inode->i_op->getattr)
> >                 return inode->i_op->getattr(mnt_userns, path, stat,
> > @@ -611,6 +617,7 @@ cp_statx(const struct kstat *stat, struct statx __u=
ser *buffer)
> >         tmp.stx_dev_major =3D MAJOR(stat->dev);
> >         tmp.stx_dev_minor =3D MINOR(stat->dev);
> >         tmp.stx_mnt_id =3D stat->mnt_id;
> > +       tmp.stx_chgattr =3D stat->chgattr;
> >=20
> >         return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
> >  }
> > diff --git a/include/linux/stat.h b/include/linux/stat.h
> > index 7df06931f25d..4a17887472f6 100644
> > --- a/include/linux/stat.h
> > +++ b/include/linux/stat.h
> > @@ -50,6 +50,7 @@ struct kstat {
> >         struct timespec64 btime;                        /* File creatio=
n time */
> >         u64             blocks;
> >         u64             mnt_id;
> > +       u64             chgattr;
> >  };
> >=20
> >  #endif
> > diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> > index 1500a0f58041..b45243a0fbc5 100644
> > --- a/include/uapi/linux/stat.h
> > +++ b/include/uapi/linux/stat.h
> > @@ -124,7 +124,7 @@ struct statx {
> >         __u32   stx_dev_minor;
> >         /* 0x90 */
> >         __u64   stx_mnt_id;
> > -       __u64   __spare2;
> > +       __u64   stx_chgattr;    /* Inode change attribute */
> >         /* 0xa0 */
> >         __u64   __spare3[12];   /* Spare space for future expansion */
> >         /* 0x100 */
> > @@ -152,6 +152,7 @@ struct statx {
> >  #define STATX_BASIC_STATS      0x000007ffU     /* The stuff in the nor=
mal stat struct */
> >  #define STATX_BTIME            0x00000800U     /* Want/got stx_btime *=
/
> >  #define STATX_MNT_ID           0x00001000U     /* Got stx_mnt_id */
> > +#define STATX_CHGATTR          0x00002000U     /* Want/git stx_chgattr=
 */
> >=20
> >  #define STATX__RESERVED                0x80000000U     /* Reserved for=
 future struct statx expansion */
> >=20
> > diff --git a/samples/vfs/test-statx.c b/samples/vfs/test-statx.c
> > index 49c7a46cee07..767208d2f564 100644
> > --- a/samples/vfs/test-statx.c
> > +++ b/samples/vfs/test-statx.c
> > @@ -109,6 +109,8 @@ static void dump_statx(struct statx *stx)
> >                 printf(" Inode: %-11llu", (unsigned long long) stx->stx=
_ino);
> >         if (stx->stx_mask & STATX_NLINK)
> >                 printf(" Links: %-5u", stx->stx_nlink);
> > +       if (stx->stx_mask & STATX_CHGATTR)
> > +               printf(" Change Attr: 0x%llx", stx->stx_chgattr);
> >         if (stx->stx_mask & STATX_TYPE) {
> >                 switch (stx->stx_mode & S_IFMT) {
> >                 case S_IFBLK:
> > @@ -218,7 +220,7 @@ int main(int argc, char **argv)
> >         struct statx stx;
> >         int ret, raw =3D 0, atflag =3D AT_SYMLINK_NOFOLLOW;
> >=20
> > -       unsigned int mask =3D STATX_BASIC_STATS | STATX_BTIME;
> > +       unsigned int mask =3D STATX_BASIC_STATS | STATX_BTIME | STATX_C=
HGATTR;
> >=20
> >         for (argv++; *argv; argv++) {
> >                 if (strcmp(*argv, "-F") =3D=3D 0) {
> > --
> > 2.37.1
> >=20
>=20

--=20
Jeff Layton <jlayton@redhat.com>