[RFC PATCH 1/4] vfs: report change attribute in statx for IS_I_VERSION inodes

[JunChao Sun]

On Sat, Aug 6, 2022 at 2:37 AM Jeff Layton <jlayton at kernel.org> wrote:
>
> From: Jeff Layton <jlayton at redhat.com>
>
> Claim one of the spare fields in struct statx to hold a 64-bit change
>>
>> attribute. When statx requests this attribute, do an
>> inode_query_iversion and fill the result in the field.

I guess, is it better to update the corresponding part of the man-pages...?
>
>
> Also update the test-statx.c program to fetch the change attribute as
> well.
>
> Signed-off-by: Jeff Layton <jlayton at 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(-)
>
> 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>
>
>  #include <linux/uaccess.h>
>  #include <asm/unistd.h>
> @@ -118,6 +119,11 @@ int vfs_getattr_nosec(const struct path *path, struct kstat *stat,
>         stat->attributes_mask |= (STATX_ATTR_AUTOMOUNT |
>                                   STATX_ATTR_DAX);
>
> +       if ((request_mask & STATX_CHGATTR) && IS_I_VERSION(inode)) {
> +               stat->result_mask |= STATX_CHGATTR;
> +               stat->chgattr = inode_query_iversion(inode);
> +       }
> +
>         mnt_userns = 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 __user *buffer)
>         tmp.stx_dev_major = MAJOR(stat->dev);
>         tmp.stx_dev_minor = MINOR(stat->dev);
>         tmp.stx_mnt_id = stat->mnt_id;
> +       tmp.stx_chgattr = stat->chgattr;
>
>         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 creation time */
>         u64             blocks;
>         u64             mnt_id;
> +       u64             chgattr;
>  };
>
>  #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 normal 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 */
>
>  #define STATX__RESERVED                0x80000000U     /* Reserved for future struct statx expansion */
>
> 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 = 0, atflag = AT_SYMLINK_NOFOLLOW;
>
> -       unsigned int mask = STATX_BASIC_STATS | STATX_BTIME;
> +       unsigned int mask = STATX_BASIC_STATS | STATX_BTIME | STATX_CHGATTR;
>
>         for (argv++; *argv; argv++) {
>                 if (strcmp(*argv, "-F") == 0) {
> --
> 2.37.1
>