xfs: spilt xfs_dialloc() into 2 functions

This patch explicitly separates free inode chunk allocation and
inode allocation into two individual high level operations.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_ialloc.c

@@ -1570,7 +1570,7 @@ xfs_dialloc_ag_update_inobt(
  * The caller selected an AG for us, and made sure that free inodes are
  * available.
  */
-STATIC int
+int
 xfs_dialloc_ag(
 	struct xfs_trans	*tp,
 	struct xfs_buf		*agbp,
@@ -1718,21 +1718,22 @@ xfs_dialloc_roll(
 }
 
 /*
- * Allocate an inode on disk.
+ * Select and prepare an AG for inode allocation.
  *
- * Mode is used to tell whether the new inode will need space, and whether it
- * is a directory.
+ * Mode is used to tell whether the new inode is a directory and hence where to
+ * locate it.
  *
- * Once we successfully pick an inode its number is returned and the on-disk
- * data structures are updated.  The inode itself is not read in, since doing so
- * would break ordering constraints with xfs_reclaim.
+ * This function will ensure that the selected AG has free inodes available to
+ * allocate from. The selected AGI will be returned locked to the caller, and it
+ * will allocate more free inodes if required. If no free inodes are found or
+ * can be allocated, no AGI will be returned.
  */
 int
-xfs_dialloc(
+xfs_dialloc_select_ag(
 	struct xfs_trans	**tpp,
 	xfs_ino_t		parent,
 	umode_t			mode,
-	xfs_ino_t		*inop)
+	struct xfs_buf		**IO_agbp)
 {
 	struct xfs_mount	*mp = (*tpp)->t_mountp;
 	struct xfs_buf		*agbp;
@@ -1745,15 +1746,15 @@ xfs_dialloc(
 	struct xfs_ino_geometry	*igeo = M_IGEO(mp);
 	bool			okalloc = true;
 
+	*IO_agbp = NULL;
+
 	/*
 	 * We do not have an agbp, so select an initial allocation
 	 * group for inode allocation.
 	 */
 	start_agno = xfs_ialloc_ag_select(*tpp, parent, mode);
-	if (start_agno == NULLAGNUMBER) {
-		*inop = NULLFSINO;
+	if (start_agno == NULLAGNUMBER)
 		return 0;
-	}
 
 	/*
 	 * If we have already hit the ceiling of inode blocks then clear
@@ -1786,7 +1787,7 @@ xfs_dialloc(
 		if (!pag->pagi_init) {
 			error = xfs_ialloc_pagi_init(mp, *tpp, agno);
 			if (error)
-				goto out_error;
+				break;
 		}
 
 		/*
@@ -1801,11 +1802,11 @@ xfs_dialloc(
 		 */
 		error = xfs_ialloc_read_agi(mp, *tpp, agno, &agbp);
 		if (error)
-			goto out_error;
+			break;
 
 		if (pag->pagi_freecount) {
 			xfs_perag_put(pag);
-			goto out_alloc;
+			goto found_ag;
 		}
 
 		if (!okalloc)
@@ -1816,12 +1817,9 @@ xfs_dialloc(
 		if (error) {
 			xfs_trans_brelse(*tpp, agbp);
 
-			if (error != -ENOSPC)
-				goto out_error;
-
-			xfs_perag_put(pag);
-			*inop = NULLFSINO;
-			return 0;
+			if (error == -ENOSPC)
+				error = 0;
+			break;
 		}
 
 		if (ialloced) {
@@ -1838,9 +1836,7 @@ xfs_dialloc(
 				xfs_buf_relse(agbp);
 				return error;
 			}
-
-			*inop = NULLFSINO;
-			goto out_alloc;
+			goto found_ag;
 		}
 
 nextag_relse_buffer:
@@ -1849,17 +1845,15 @@ xfs_dialloc(
 		xfs_perag_put(pag);
 		if (++agno == mp->m_sb.sb_agcount)
 			agno = 0;
-		if (agno == start_agno) {
-			*inop = NULLFSINO;
+		if (agno == start_agno)
 			return noroom ? -ENOSPC : 0;
-		}
 	}
 
-out_alloc:
-	return xfs_dialloc_ag(*tpp, agbp, parent, inop);
-out_error:
 	xfs_perag_put(pag);
 	return error;
+found_ag:
+	*IO_agbp = agbp;
+	return 0;
 }
 
 /*

fs/xfs/libxfs/xfs_ialloc.h

@@ -37,16 +37,26 @@ xfs_make_iptr(struct xfs_mount *mp, struct xfs_buf *b, int o)
  * Mode is used to tell whether the new inode will need space, and whether
  * it is a directory.
  *
- * Once we successfully pick an inode its number is returned and the
- * on-disk data structures are updated.  The inode itself is not read
- * in, since doing so would break ordering constraints with xfs_reclaim.
+ * There are two phases to inode allocation: selecting an AG and ensuring
+ * that it contains free inodes, followed by allocating one of the free
+ * inodes. xfs_dialloc_select_ag() does the former and returns a locked AGI
+ * to the caller, ensuring that followup call to xfs_dialloc_ag() will
+ * have free inodes to allocate from. xfs_dialloc_ag() will return the inode
+ * number of the free inode we allocated.
  */
 int					/* error */
-xfs_dialloc(
+xfs_dialloc_select_ag(
 	struct xfs_trans **tpp,		/* double pointer of transaction */
 	xfs_ino_t	parent,		/* parent inode (directory) */
 	umode_t		mode,		/* mode bits for new inode */
-	xfs_ino_t	*inop);		/* inode number allocated */
+	struct xfs_buf	**IO_agbp);
+
+int
+xfs_dialloc_ag(
+	struct xfs_trans	*tp,
+	struct xfs_buf		*agbp,
+	xfs_ino_t		parent,
+	xfs_ino_t		*inop);
 
 /*
  * Free disk inode.  Carefully avoids touching the incore inode, all

fs/xfs/xfs_inode.c

@@ -909,6 +909,7 @@ xfs_dir_ialloc(
 	prid_t			prid,
 	struct xfs_inode	**ipp)
 {
+	struct xfs_buf		*agibp;
 	xfs_ino_t		parent_ino = dp ? dp->i_ino : 0;
 	xfs_ino_t		ino;
 	int			error;
@@ -919,13 +920,19 @@ xfs_dir_ialloc(
 	 * Call the space management code to pick the on-disk inode to be
 	 * allocated.
 	 */
-	error = xfs_dialloc(tpp, parent_ino, mode, &ino);
+	error = xfs_dialloc_select_ag(tpp, parent_ino, mode, &agibp);
 	if (error)
 		return error;
 
-	if (ino == NULLFSINO)
+	if (!agibp)
 		return -ENOSPC;
 
+	/* Allocate an inode from the selected AG */
+	error = xfs_dialloc_ag(*tpp, agibp, parent_ino, &ino);
+	if (error)
+		return error;
+	ASSERT(ino != NULLFSINO);
+
 	return xfs_init_new_inode(*tpp, dp, ino, mode, nlink, rdev, prid, ipp);
 }