[PATCH 4/5] xfs: enable userspace to hide an AG from allocation

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

Add an administrative interface so that userspace can hide an allocation
group from block allocation.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/libxfs/xfs_ag.c |   54 ++++++++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/libxfs/xfs_fs.h |    5 ++++
 fs/xfs/xfs_ioctl.c     |    4 +++-
 3 files changed, 62 insertions(+), 1 deletion(-)


diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index a855f943cfad9..183f46edb5d15 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -1075,6 +1075,54 @@ xfs_ag_extend_space(
 	return 0;
 }
 
+/* Compute the AG geometry flags. */
+static inline uint32_t
+xfs_ag_calc_geoflags(
+	struct xfs_perag	*pag)
+{
+	uint32_t		ret = 0;
+
+	if (xfs_perag_prohibits_alloc(pag))
+		ret |= XFS_AG_FLAG_NOALLOC;
+
+	return ret;
+}
+
+/*
+ * Compare the current AG geometry flags against the flags in the AG geometry
+ * structure and update the AG state to reflect any changes, then update the
+ * struct to reflect the current status.
+ */
+static inline int
+xfs_ag_update_geoflags(
+	struct xfs_perag	*pag,
+	struct xfs_ag_geometry	*ageo,
+	uint32_t		new_flags)
+{
+	uint32_t		old_flags = xfs_ag_calc_geoflags(pag);
+	int			error;
+
+	if (!(new_flags & XFS_AG_FLAG_UPDATE)) {
+		ageo->ag_flags = old_flags;
+		return 0;
+	}
+
+	if ((old_flags & XFS_AG_FLAG_NOALLOC) &&
+	    !(new_flags & XFS_AG_FLAG_NOALLOC)) {
+		xfs_ag_clear_noalloc(pag);
+	}
+
+	if (!(old_flags & XFS_AG_FLAG_NOALLOC) &&
+	    (new_flags & XFS_AG_FLAG_NOALLOC)) {
+		error = xfs_ag_set_noalloc(pag);
+		if (error)
+			return error;
+	}
+
+	ageo->ag_flags = xfs_ag_calc_geoflags(pag);
+	return 0;
+}
+
 /* Retrieve AG geometry. */
 int
 xfs_ag_get_geometry(
@@ -1086,6 +1134,7 @@ xfs_ag_get_geometry(
 	struct xfs_agi		*agi;
 	struct xfs_agf		*agf;
 	unsigned int		freeblks;
+	uint32_t		inflags = ageo->ag_flags;
 	int			error;
 
 	/* Lock the AG headers. */
@@ -1096,6 +1145,10 @@ xfs_ag_get_geometry(
 	if (error)
 		goto out_agi;
 
+	error = xfs_ag_update_geoflags(pag, ageo, inflags);
+	if (error)
+		goto out;
+
 	/* Fill out form. */
 	memset(ageo, 0, sizeof(*ageo));
 	ageo->ag_number = pag->pag_agno;
@@ -1113,6 +1166,7 @@ xfs_ag_get_geometry(
 	ageo->ag_freeblks = freeblks;
 	xfs_ag_geom_health(pag, ageo);
 
+out:
 	/* Release resources. */
 	xfs_buf_relse(agf_bp);
 out_agi:
diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
index 4159e96d01ae6..96688f9301e08 100644
--- a/fs/xfs/libxfs/xfs_fs.h
+++ b/fs/xfs/libxfs/xfs_fs.h
@@ -305,6 +305,11 @@ struct xfs_ag_geometry {
 #define XFS_AG_GEOM_SICK_REFCNTBT (1 << 9)  /* reference counts */
 #define XFS_AG_GEOM_SICK_INODES	(1 << 10) /* bad inodes were seen */
 
+#define XFS_AG_FLAG_UPDATE	(1 << 0)  /* update flags */
+#define XFS_AG_FLAG_NOALLOC	(1 << 1)  /* do not allocate from this AG */
+#define XFS_AG_FLAG_ALL		(XFS_AG_FLAG_UPDATE | \
+				 XFS_AG_FLAG_NOALLOC)
+
 /*
  * Structures for XFS_IOC_FSGROWFSDATA, XFS_IOC_FSGROWFSLOG & XFS_IOC_FSGROWFSRT
  */
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index f85d5f142d180..d17b17e7eea1d 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -976,10 +976,12 @@ xfs_ioc_ag_geometry(
 
 	if (copy_from_user(&ageo, arg, sizeof(ageo)))
 		return -EFAULT;
-	if (ageo.ag_flags)
+	if (ageo.ag_flags & ~XFS_AG_FLAG_ALL)
 		return -EINVAL;
 	if (memchr_inv(&ageo.ag_reserved, 0, sizeof(ageo.ag_reserved)))
 		return -EINVAL;
+	if ((ageo.ag_flags & XFS_AG_FLAG_UPDATE) && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
 
 	pag = xfs_perag_get(mp, ageo.ag_number);
 	if (!pag)