[PATCH 02/21] xfs: create a new helper to return a file's allocation unit

["Darrick J. Wong" <djwong@xxxxxxxxxx>]

From: Darrick J. Wong <djwong@xxxxxxxxxx>

Create a new helper function to calculate the fundamental allocation
unit (i.e. the smallest unit of space we can allocate) of a file.
Things are going to get hairy with range-exchange on the realtime
device, so prepare for this now.

Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
 fs/xfs/xfs_file.c  |   26 +++++++++-----------------
 fs/xfs/xfs_inode.c |   13 +++++++++++++
 fs/xfs/xfs_inode.h |    1 +
 3 files changed, 23 insertions(+), 17 deletions(-)


diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index c4bdadd8fa71..b382380656d7 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -44,27 +44,19 @@ xfs_is_falloc_aligned(
 	loff_t			pos,
 	long long int		len)
 {
-	struct xfs_mount	*mp = ip->i_mount;
-	uint64_t		mask;
+	unsigned int		alloc_unit = xfs_inode_alloc_unitsize(ip);
 
-	if (XFS_IS_REALTIME_INODE(ip)) {
-		if (!is_power_of_2(mp->m_sb.sb_rextsize)) {
-			u64	rextbytes;
-			u32	mod;
+	if (XFS_IS_REALTIME_INODE(ip) && !is_power_of_2(alloc_unit)) {
+		u32	mod;
 
-			rextbytes = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize);
-			div_u64_rem(pos, rextbytes, &mod);
-			if (mod)
-				return false;
-			div_u64_rem(len, rextbytes, &mod);
-			return mod == 0;
-		}
-		mask = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize) - 1;
-	} else {
-		mask = mp->m_sb.sb_blocksize - 1;
+		div_u64_rem(pos, alloc_unit, &mod);
+		if (mod)
+			return false;
+		div_u64_rem(len, alloc_unit, &mod);
+		return mod == 0;
 	}
 
-	return !((pos | len) & mask);
+	return !((pos | len) & (alloc_unit - 1));
 }
 
 /*
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index b082222a9061..04ceafb936bc 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -3795,3 +3795,16 @@ xfs_inode_count_blocks(
 	xfs_bmap_count_leaves(ifp, rblocks);
 	*dblocks = ip->i_nblocks - *rblocks;
 }
+
+/* Returns the size of fundamental allocation unit for a file, in bytes. */
+unsigned int
+xfs_inode_alloc_unitsize(
+	struct xfs_inode	*ip)
+{
+	unsigned int		blocks = 1;
+
+	if (XFS_IS_REALTIME_INODE(ip))
+		blocks = ip->i_mount->m_sb.sb_rextsize;
+
+	return XFS_FSB_TO_B(ip->i_mount, blocks);
+}
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 926e4dd566d0..4b01d078ace2 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -577,6 +577,7 @@ void xfs_iunlock2_io_mmap(struct xfs_inode *ip1, struct xfs_inode *ip2);
 
 void xfs_inode_count_blocks(struct xfs_trans *tp, struct xfs_inode *ip,
 		xfs_filblks_t *dblocks, xfs_filblks_t *rblocks);
+unsigned int xfs_inode_alloc_unitsize(struct xfs_inode *ip);
 
 /*
  * Parameters for tracking bumplink and droplink operations.  The hook