xfs: fix fallocate functions when rtextsize is larger than 1

In commit fe341eb1, I forgot that xfs_free_file_space isn't strictly
a "remove mapped blocks" function.  It is actually a function to zero
file space by punching out the middle and writing zeroes to the
unaligned ends of the specified range.  Therefore, putting a rtextsize
alignment check in that function is wrong because that breaks unaligned
ZERO_RANGE on the realtime volume.

Furthermore, xfs_file_fallocate already has alignment checks for the
functions require the file range to be aligned to the size of a
fundamental allocation unit (which is 1 FSB on the data volume and 1 rt
extent on the realtime volume).  Create a new helper to check fallocate
arguments against the realtiem allocation unit size, fix the fallocate
frontend to use it, fix free_file_space to delete the correct range, and
remove a now redundant check from insert_file_space.

NOTE: The realtime extent size is not required to be a power of two!

Fixes: fe341eb1 ("xfs: ensure that fpunch, fcollapse, and finsert operations are aligned to rt extent size")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>

fs/xfs/xfs_bmap_util.c

@@ -947,11 +947,11 @@ xfs_free_file_space(
 	endoffset_fsb = XFS_B_TO_FSBT(mp, offset + len);
 
 	/* We can only free complete realtime extents. */
-	if (XFS_IS_REALTIME_INODE(ip)) {
-		xfs_extlen_t	extsz = xfs_get_extsz_hint(ip);
-
-		if ((startoffset_fsb | endoffset_fsb) & (extsz - 1))
-			return -EINVAL;
+	if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1) {
+		startoffset_fsb = roundup_64(startoffset_fsb,
+					     mp->m_sb.sb_rextsize);
+		endoffset_fsb = rounddown_64(endoffset_fsb,
+					     mp->m_sb.sb_rextsize);
 	}
 
 	/*
@@ -1147,14 +1147,6 @@ xfs_insert_file_space(
 
 	trace_xfs_insert_file_space(ip);
 
-	/* We can only insert complete realtime extents. */
-	if (XFS_IS_REALTIME_INODE(ip)) {
-		xfs_extlen_t	extsz = xfs_get_extsz_hint(ip);
-
-		if ((stop_fsb | shift_fsb) & (extsz - 1))
-			return -EINVAL;
-	}
-
 	error = xfs_bmap_can_insert_extents(ip, stop_fsb, shift_fsb);
 	if (error)
 		return error;

fs/xfs/xfs_file.c

@@ -32,6 +32,39 @@
 
 static const struct vm_operations_struct xfs_file_vm_ops;
 
+/*
+ * Decide if the given file range is aligned to the size of the fundamental
+ * allocation unit for the file.
+ */
+static bool
+xfs_is_falloc_aligned(
+	struct xfs_inode	*ip,
+	loff_t			pos,
+	long long int		len)
+{
+	struct xfs_mount	*mp = ip->i_mount;
+	uint64_t		mask;
+
+	if (XFS_IS_REALTIME_INODE(ip)) {
+		if (!is_power_of_2(mp->m_sb.sb_rextsize)) {
+			u64	rextbytes;
+			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;
+	}
+
+	return !((pos | len) & mask);
+}
+
 int
 xfs_update_prealloc_flags(
 	struct xfs_inode	*ip,
@@ -850,9 +883,7 @@ xfs_file_fallocate(
 		if (error)
 			goto out_unlock;
 	} else if (mode & FALLOC_FL_COLLAPSE_RANGE) {
-		unsigned int blksize_mask = i_blocksize(inode) - 1;
-
-		if (offset & blksize_mask || len & blksize_mask) {
+		if (!xfs_is_falloc_aligned(ip, offset, len)) {
 			error = -EINVAL;
 			goto out_unlock;
 		}
@@ -872,10 +903,9 @@ xfs_file_fallocate(
 		if (error)
 			goto out_unlock;
 	} else if (mode & FALLOC_FL_INSERT_RANGE) {
-		unsigned int	blksize_mask = i_blocksize(inode) - 1;
 		loff_t		isize = i_size_read(inode);
 
-		if (offset & blksize_mask || len & blksize_mask) {
+		if (!xfs_is_falloc_aligned(ip, offset, len)) {
 			error = -EINVAL;
 			goto out_unlock;
 		}

fs/xfs/xfs_linux.h

@@ -175,6 +175,12 @@ static inline xfs_dev_t linux_to_xfs_dev_t(dev_t dev)
 #define xfs_sort(a,n,s,fn)	sort(a,n,s,fn,NULL)
 #define xfs_stack_trace()	dump_stack()
 
+static inline uint64_t rounddown_64(uint64_t x, uint32_t y)
+{
+	do_div(x, y);
+	return x * y;
+}
+
 static inline uint64_t roundup_64(uint64_t x, uint32_t y)
 {
 	x += y - 1;