xfs: implement XFS_IOC_DIOINFO in terms of vfs_getattr

Use the direct I/O alignment reporting from ->getattr instead of
reimplementing it.  This exposes the relaxation of the memory
alignment in the XFS_IOC_DIOINFO info and ensure the information will
stay in sync.  Note that randholes.c in xfstests has a bug where it
incorrectly fails when the required memory alignment is smaller than the
pointer size.  Round up the reported value as there is a fair chance that
this code got copied into various applications.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

1 files changed, 9 insertions, 9 deletions

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 10a3a5160f4e..a6bb7ee7a27a 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1203,21 +1203,21 @@ xfs_file_ioctl(
 				current->comm);
 		return -ENOTTY;
 	case XFS_IOC_DIOINFO: {
-		struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
+		struct kstat		st;
 		struct dioattr		da;
 
-		da.d_mem = target->bt_logical_sectorsize;
+		error = vfs_getattr(&filp->f_path, &st, STATX_DIOALIGN, 0);
+		if (error)
+			return error;
 
 		/*
-		 * See xfs_report_dioalign() for an explanation about why this
-		 * reports a value larger than the sector size for COW inodes.
+		 * Some userspace directly feeds the return value to
+		 * posix_memalign, which fails for values that are smaller than
+		 * the pointer size.  Round up the value to not break userspace.
 		 */
-		if (xfs_is_cow_inode(ip))
-			da.d_miniosz = xfs_inode_alloc_unitsize(ip);
-		else
-			da.d_miniosz = target->bt_logical_sectorsize;
+		da.d_mem = roundup(st.dio_mem_align, sizeof(void *));
+		da.d_miniosz = st.dio_offset_align;
 		da.d_maxiosz = INT_MAX & ~(da.d_miniosz - 1);
-
 		if (copy_to_user(arg, &da, sizeof(da)))
 			return -EFAULT;
 		return 0;