Add a new statx field for (sub)volume identifiers, as implemented by
btrfs and bcachefs.

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]>
Signed-off-by: Kent Overstreet <[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..6a542ed43e2c 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->subvol    = inode->ei_subvol;
+       stat->result_mask |= STATX_SUBVOL;
+
        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..70bd3e888cfa 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_subvol = stat->subvol;
 
        return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
 }
diff --git a/include/linux/stat.h b/include/linux/stat.h
index 52150570d37a..bf92441dbad2 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             subvol;
 };
 
 /* 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..67626d535316 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_subvol;     /* Subvolume identifier */
        /* 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_SUBVOL           0x00008000U     /* Want/got stx_subvol */
 
 #define STATX__RESERVED                0x80000000U     /* Reserved for future 
struct statx expansion */
 
-- 
2.43.0


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