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

[Jeff Layton]

On Mon, 2022-08-08 at 10:09 +0800, Xiubo Li wrote:
> On 8/6/22 2:35 AM, Jeff Layton 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.
> > 
> > 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 */
> 
> s/git/get/ ?
> 

Muscle-memory typo. Fixed in my tree.

> >   
> >   #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) {
> 

Thanks,
-- 
Jeff Layton <jlayton at kernel.org>