>>>>> "Kent" == Kent Overstreet <[email protected]> writes:

> Add a new statx field for (sub)volume identifiers.
> This includes bcachefs support; we'll definitely want btrfs support as
> well.

> Link: 
> https://lore.kernel.org/linux-fsdevel/2uvhm6gweyl7iyyp2xpfryvcu2g3padagaeqcbiavjyiis6prl@yjm725bizncq/
> Signed-off-by: Kent Overstreet <[email protected]>
> Cc: Josef Bacik <[email protected]>
> Cc: Miklos Szeredi <[email protected]>
> Cc: Christian Brauner <[email protected]>
> Cc: David Howells <[email protected]>
> ---
>  fs/bcachefs/fs.c          | 3 +++
>  fs/stat.c                 | 1 +
>  include/linux/stat.h      | 1 +
>  include/uapi/linux/stat.h | 4 +++-
>  4 files changed, 8 insertions(+), 1 deletion(-)

> diff --git a/fs/bcachefs/fs.c b/fs/bcachefs/fs.c
> index 3f073845bbd7..d82f7f3f0670 100644
> --- a/fs/bcachefs/fs.c
> +++ b/fs/bcachefs/fs.c
> @@ -840,6 +840,9 @@ static int bch2_getattr(struct mnt_idmap *idmap,
stat-> blksize  = block_bytes(c);
stat-> blocks   = inode->v.i_blocks;
 
> +     stat->vol       = inode->ei_subvol;
> +     stat->result_mask |= STATX_VOL;
> +
>       if (request_mask & STATX_BTIME) {
stat-> result_mask |= STATX_BTIME;
stat-> btime = bch2_time_to_timespec(c, inode->ei_inode.bi_otime);
> diff --git a/fs/stat.c b/fs/stat.c
> index 77cdc69eb422..80d5f7502d99 100644
> --- a/fs/stat.c
> +++ b/fs/stat.c
> @@ -658,6 +658,7 @@ 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_vol = stat->vol;

So this bugs me that you use subvol and vol sorta interchangeably
here.  Shouldn't it always be 'subvol'?  It's not a seperate volume,
it's a snapshot/whatever that is a part of the parent volume, but
should be treated seperately. 
 
>       return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
>  }
> diff --git a/include/linux/stat.h b/include/linux/stat.h
> index 52150570d37a..9dc1b493ef1f 100644
> --- a/include/linux/stat.h
> +++ b/include/linux/stat.h
> @@ -53,6 +53,7 @@ struct kstat {
>       u32             dio_mem_align;
>       u32             dio_offset_align;
>       u64             change_cookie;
> +     u64             vol;
>  };

Again, should this be subvol? And comments added for what it really means?
 
>  /* These definitions are internal to the kernel for now. Mainly used by 
> nfsd. */
> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> index 2f2ee82d5517..ae090d67946d 100644
> --- a/include/uapi/linux/stat.h
> +++ b/include/uapi/linux/stat.h
> @@ -126,8 +126,9 @@ struct statx {
>       __u64   stx_mnt_id;
>       __u32   stx_dio_mem_align;      /* Memory buffer alignment for direct 
> I/O */
>       __u32   stx_dio_offset_align;   /* File offset alignment for direct I/O 
> */
> +     __u64   stx_vol;        /* Subvolume identifier */

Again, then call it 'stx_subvol' if that's what it is!

>       /* 0xa0 */
> -     __u64   __spare3[12];   /* Spare space for future expansion */
> +     __u64   __spare3[11];   /* Spare space for future expansion */
>       /* 0x100 */
>  };
 
> @@ -155,6 +156,7 @@ struct statx {
>  #define STATX_MNT_ID         0x00001000U     /* Got stx_mnt_id */
>  #define STATX_DIOALIGN               0x00002000U     /* Want/got direct I/O 
> alignment info */
>  #define STATX_MNT_ID_UNIQUE  0x00004000U     /* Want/got extended 
> stx_mount_id */
> +#define STATX_VOL            0x00008000U     /* Want/got stx_vol */
 
>  #define STATX__RESERVED              0x80000000U     /* Reserved for future 
> struct statx expansion */
 
> -- 
> 2.43.0



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