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

[Xiubo Li <xiubli@redhat.com>]

On 8/6/22 2:35 AM, Jeff Layton wrote:
> From: Jeff Layton <jlayton@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.
>
> Also update the test-statx.c program to fetch the change attribute as
> well.
>
> 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(-)
>
> 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 */

s/git/get/ ?

>   
>   #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) {