We need to check if an affected AG is empty or not during FS shrink, this is a helper could be used for this purpose.
Maybe it's better to isolate AG related routines to a dedicated file: xfs_ag.c?
Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
---
fs/xfs/xfs_fsops.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 92 insertions(+), 0 deletions(-)
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 029ab6d..6623d9a 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -614,6 +614,98 @@ xfs_growfs_log(
}
/*
+ * Get the reserved blocks of metadatas per AG which are includes:
+ * Superblock (1 sector)
+ * AG free block info (1 sector)
+ * AG inode B+tree info (1 sector)
+ * AG internal free list (1 sector)
+ * Root of inode B+tree (1 block)
+ * Root of free space B+tree, key is block number (1 block)
+ * Root of free space B+tree, key is block count (1 block)
+ * Free list (4 blocks)
+ * The reserved block number of the aboves can be fetched via:
+ * XFS_PREALLOC_BLOCKS(mp).
+ *
+ * The left blocks are used for Primary AG only.
+ * - Inodes (64 inodes)
+ */
+static xfs_extlen_t
+xfs_ag_metadata_blocks(
+ xfs_mount_t *mp,
+ xfs_agnumber_t agno)
+{
+ xfs_extlen_t mdblocks;
+
+ mdblocks = XFS_PREALLOC_BLOCKS(mp);
+ /*
+ * For primary AG, we need to figure out how many blocks are
+ * reserved for those 64 inodes which are used for the root
+ * of inodes B+tree.
+ */
+ if (agno == 0)
+ mdblocks += (64 / mp->m_sb.sb_inopblock);
+
+ return mdblocks;
+}
+
+/*
+ * An empty AG means that there has no data/inodes allocated
+ * at it except those metadata blocks, and the agi_count should
+ * be ZERO.
+ */
+static int
+xfs_ag_is_empty(
+ xfs_mount_t *mp,
+ xfs_agnumber_t agno,
+ bool *empty)
+{
+ xfs_extlen_t agblocks;
+ xfs_extlen_t agfblocks;
+ xfs_extlen_t agmblocks;
+ xfs_extlen_t agicount;
+ xfs_agf_t *agf;
+ xfs_agi_t *agi;
+ xfs_buf_t *bp;
+ int error = 0;
+
+ bp = xfs_buf_get(mp->m_ddev_targp,
+ XFS_AG_DADDR(mp, agno, XFS_AGF_DADDR(mp)),
+ XFS_FSS_TO_BB(mp, 1), 0);
+ if (!bp) {
+ error = XFS_ERROR(ENOMEM);
+ goto error0;
+ }
+ agf = XFS_BUF_TO_AGF(bp);
+ agmblocks = xfs_ag_metadata_blocks(mp, agno);
+ /*
+ * The latest AG might has different size to others.
+ */
+ if (agno == mp->m_sb.sb_agcount - 1)
+ agblocks = (be32_to_cpu(agf->agf_length) - agmblocks);
+ else
+ agblocks = mp->m_sb.sb_agblocks - agmblocks;
+ agfblocks = be32_to_cpu(agf->agf_freeblks);
+ xfs_buf_relse(bp);
+
+ bp = xfs_buf_get(mp->m_ddev_targp,
+ XFS_AG_DADDR(mp, agno, XFS_AGI_DADDR(mp)),
+ XFS_FSS_TO_BB(mp, 1), 0);
+ if (!bp) {
+ error = XFS_ERROR(ENOMEM);
+ goto error0;
+ }
+ agi = XFS_BUF_TO_AGI(bp);
+ agicount = be32_to_cpu(agi->agi_count);
+ xfs_buf_relse(bp);
+
+ *empty = ((agblocks == agfblocks && agicount == 0) ?
+ true : false);
+
+error0:
+ return error;
+}
+
+/*
* exported through ioctl XFS_IOC_FSCOUNTS
*/
--
1.7.4.1
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