[PATCH] xfs: add write pointer to xfs_rtgroup_geometry

[Wilfred Mallawa <wilfred.opensource@gmail.com>]

From: Wilfred Mallawa <wilfred.mallawa@wdc.com>

There is currently no XFS ioctl that allows userspace to retrieve the
write pointer for a specific realtime group block for zoned XFS. On zoned
block devices, userspace can obtain this information via zone reports from
the underlying device. However, for zoned XFS operating on regular block
devices, no equivalent mechanism exists.

Access to the realtime group write pointer is useful to userspace
development and analysis tools such as Zonar [1]. So extend the existing
struct xfs_rtgroup_geometry to add a new rg_writepointer field. This field
is valid if XFS_RTGROUP_GEOM_WRITEPOINTER flag is set. The rg_writepointer
field specifies the location of the current writepointer as a sector offset
into the respective rtgroup.

[1] https://lwn.net/Articles/1059364/
Signed-off-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
---
 fs/xfs/libxfs/xfs_fs.h |  6 +++++-
 fs/xfs/xfs_ioctl.c     | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
index d165de607d17..ca63ae67f16c 100644
--- a/fs/xfs/libxfs/xfs_fs.h
+++ b/fs/xfs/libxfs/xfs_fs.h
@@ -995,7 +995,9 @@ struct xfs_rtgroup_geometry {
 	__u32 rg_sick;		/* o: sick things in ag */
 	__u32 rg_checked;	/* o: checked metadata in ag */
 	__u32 rg_flags;		/* i/o: flags for this ag */
-	__u32 rg_reserved[27];	/* o: zero */
+	__u32 rg_reserved0;	/* o: preserve alignment */
+	__u64 rg_writepointer;  /* o: write pointer sector for zoned */
+	__u32 rg_reserved[24];	/* o: zero */
 };
 #define XFS_RTGROUP_GEOM_SICK_SUPER	(1U << 0)  /* superblock */
 #define XFS_RTGROUP_GEOM_SICK_BITMAP	(1U << 1)  /* rtbitmap */
@@ -1003,6 +1005,8 @@ struct xfs_rtgroup_geometry {
 #define XFS_RTGROUP_GEOM_SICK_RMAPBT	(1U << 3)  /* reverse mappings */
 #define XFS_RTGROUP_GEOM_SICK_REFCNTBT	(1U << 4)  /* reference counts */
 
+#define XFS_RTGROUP_GEOM_WRITEPOINTER  (1U << 0)  /* write pointer */
+
 /* Health monitor event domains */
 
 /* affects the whole fs */
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index facffdc8dca8..86bd8fc0c41d 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -37,12 +37,15 @@
 #include "xfs_ioctl.h"
 #include "xfs_xattr.h"
 #include "xfs_rtbitmap.h"
+#include "xfs_rtrmap_btree.h"
 #include "xfs_file.h"
 #include "xfs_exchrange.h"
 #include "xfs_handle.h"
 #include "xfs_rtgroup.h"
 #include "xfs_healthmon.h"
 #include "xfs_verify_media.h"
+#include "xfs_zone_priv.h"
+#include "xfs_zone_alloc.h"
 
 #include <linux/mount.h>
 #include <linux/fileattr.h>
@@ -413,6 +416,7 @@ xfs_ioc_rtgroup_geometry(
 {
 	struct xfs_rtgroup	*rtg;
 	struct xfs_rtgroup_geometry rgeo;
+	xfs_rgblock_t		highest_rgbno, write_pointer;
 	int			error;
 
 	if (copy_from_user(&rgeo, arg, sizeof(rgeo)))
@@ -433,6 +437,22 @@ xfs_ioc_rtgroup_geometry(
 	if (error)
 		return error;
 
+	if (xfs_has_zoned(mp)) {
+		xfs_rtgroup_lock(rtg, XFS_RTGLOCK_RMAP);
+		if (rtg->rtg_open_zone) {
+			write_pointer = rtg->rtg_open_zone->oz_allocated;
+		} else {
+			highest_rgbno = xfs_rtrmap_highest_rgbno(rtg);
+			if (highest_rgbno == NULLRGBLOCK)
+				write_pointer = 0;
+			else
+				write_pointer = highest_rgbno + 1;
+		}
+		xfs_rtgroup_unlock(rtg, XFS_RTGLOCK_RMAP);
+		rgeo.rg_writepointer = XFS_FSB_TO_BB(mp, write_pointer);
+		rgeo.rg_flags |= XFS_RTGROUP_GEOM_WRITEPOINTER;
+	}
+
 	if (copy_to_user(arg, &rgeo, sizeof(rgeo)))
 		return -EFAULT;
 	return 0;
-- 
2.53.0