Re: [PATCH v6 7/9] vfs: expose STATX_VERSION to userland

[NeilBrown]

On Fri, 30 Sep 2022, Jeff Layton wrote:
> From: Jeff Layton <jlayton@xxxxxxxxxx>
> 
> Claim one of the spare fields in struct statx to hold a 64-bit inode
> version attribute. When userland requests STATX_VERSION, copy the
> value from the kstat struct there, and stop masking off
> STATX_ATTR_VERSION_MONOTONIC.
> 
> Update the test-statx sample program to output the change attr and
> MountId.
> 
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  fs/stat.c                 | 12 +++---------
>  include/linux/stat.h      |  9 ---------
>  include/uapi/linux/stat.h |  6 ++++--
>  samples/vfs/test-statx.c  |  8 ++++++--
>  4 files changed, 13 insertions(+), 22 deletions(-)
> 
> diff --git a/fs/stat.c b/fs/stat.c
> index e7f8cd4b24e1..8396c372022f 100644
> --- a/fs/stat.c
> +++ b/fs/stat.c
> @@ -593,11 +593,9 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
>  
>  	memset(&tmp, 0, sizeof(tmp));
>  
> -	/* STATX_VERSION is kernel-only for now */
> -	tmp.stx_mask = stat->result_mask & ~STATX_VERSION;
> +	tmp.stx_mask = stat->result_mask;
>  	tmp.stx_blksize = stat->blksize;
> -	/* STATX_ATTR_VERSION_MONOTONIC is kernel-only for now */
> -	tmp.stx_attributes = stat->attributes & ~STATX_ATTR_VERSION_MONOTONIC;
> +	tmp.stx_attributes = stat->attributes;
>  	tmp.stx_nlink = stat->nlink;
>  	tmp.stx_uid = from_kuid_munged(current_user_ns(), stat->uid);
>  	tmp.stx_gid = from_kgid_munged(current_user_ns(), stat->gid);
> @@ -621,6 +619,7 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
>  	tmp.stx_mnt_id = stat->mnt_id;
>  	tmp.stx_dio_mem_align = stat->dio_mem_align;
>  	tmp.stx_dio_offset_align = stat->dio_offset_align;
> +	tmp.stx_version = stat->version;
>  
>  	return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
>  }
> @@ -636,11 +635,6 @@ int do_statx(int dfd, struct filename *filename, unsigned int flags,
>  	if ((flags & AT_STATX_SYNC_TYPE) == AT_STATX_SYNC_TYPE)
>  		return -EINVAL;
>  
> -	/* STATX_VERSION is kernel-only for now. Ignore requests
> -	 * from userland.
> -	 */
> -	mask &= ~STATX_VERSION;
> -
>  	error = vfs_statx(dfd, filename, flags, &stat, mask);
>  	if (error)
>  		return error;
> diff --git a/include/linux/stat.h b/include/linux/stat.h
> index 4e9428d86a3a..69c79e4fd1b1 100644
> --- a/include/linux/stat.h
> +++ b/include/linux/stat.h
> @@ -54,13 +54,4 @@ struct kstat {
>  	u32		dio_offset_align;
>  	u64		version;
>  };
> -
> -/* These definitions are internal to the kernel for now. Mainly used by nfsd. */
> -
> -/* mask values */
> -#define STATX_VERSION		0x40000000U	/* Want/got stx_change_attr */
> -
> -/* file attribute values */
> -#define STATX_ATTR_VERSION_MONOTONIC	0x8000000000000000ULL /* version monotonically increases */
> -
>  #endif
> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> index 7cab2c65d3d7..4a0a1f27c059 100644
> --- a/include/uapi/linux/stat.h
> +++ b/include/uapi/linux/stat.h
> @@ -127,7 +127,8 @@ struct statx {
>  	__u32	stx_dio_mem_align;	/* Memory buffer alignment for direct I/O */
>  	__u32	stx_dio_offset_align;	/* File offset alignment for direct I/O */
>  	/* 0xa0 */
> -	__u64	__spare3[12];	/* Spare space for future expansion */
> +	__u64	stx_version; /* Inode change attribute */
> +	__u64	__spare3[11];	/* Spare space for future expansion */
>  	/* 0x100 */
>  };
>  
> @@ -154,6 +155,7 @@ struct statx {
>  #define STATX_BTIME		0x00000800U	/* Want/got stx_btime */
>  #define STATX_MNT_ID		0x00001000U	/* Got stx_mnt_id */
>  #define STATX_DIOALIGN		0x00002000U	/* Want/got direct I/O alignment info */
> +#define STATX_VERSION		0x00004000U	/* Want/got stx_version */
>  
>  #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
>  
> @@ -189,6 +191,6 @@ struct statx {
>  #define STATX_ATTR_MOUNT_ROOT		0x00002000 /* Root of a mount */
>  #define STATX_ATTR_VERITY		0x00100000 /* [I] Verity protected file */
>  #define STATX_ATTR_DAX			0x00200000 /* File is currently in DAX state */
> -
> +#define STATX_ATTR_VERSION_MONOTONIC	0x00400000 /* stx_version increases w/ every change */
>  
>  #endif /* _UAPI_LINUX_STAT_H */
> diff --git a/samples/vfs/test-statx.c b/samples/vfs/test-statx.c
> index 49c7a46cee07..bdbc371c9774 100644
> --- a/samples/vfs/test-statx.c
> +++ b/samples/vfs/test-statx.c
> @@ -107,6 +107,8 @@ static void dump_statx(struct statx *stx)
>  	printf("Device: %-15s", buffer);
>  	if (stx->stx_mask & STATX_INO)
>  		printf(" Inode: %-11llu", (unsigned long long) stx->stx_ino);
> +	if (stx->stx_mask & STATX_MNT_ID)
> +		printf(" MountId: %llx", stx->stx_mnt_id);
>  	if (stx->stx_mask & STATX_NLINK)
>  		printf(" Links: %-5u", stx->stx_nlink);
>  	if (stx->stx_mask & STATX_TYPE) {
> @@ -145,7 +147,9 @@ static void dump_statx(struct statx *stx)
>  	if (stx->stx_mask & STATX_CTIME)
>  		print_time("Change: ", &stx->stx_ctime);
>  	if (stx->stx_mask & STATX_BTIME)
> -		print_time(" Birth: ", &stx->stx_btime);
> +		print_time("Birth: ", &stx->stx_btime);
> +	if (stx->stx_mask & STATX_VERSION)
> +		printf("Inode Version: 0x%llx\n", stx->stx_version);

Why hex? not decimal?  I don't really care but it seems like an odd choice.

>  
>  	if (stx->stx_attributes_mask) {
>  		unsigned char bits, mbits;
> @@ -218,7 +222,7 @@ 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_MNT_ID | STATX_VERSION;
>  
>  	for (argv++; *argv; argv++) {
>  		if (strcmp(*argv, "-F") == 0) {
> -- 
> 2.37.3
> 
> 

Reviewed-by: NeilBrown <neilb@xxxxxxx>

Thanks,
NeilBrown