Re: [PATCH v2] xfs: don't set v3 xflags for v2 inodes

[Christoph Hellwig <hch@infradead.org>]

On Thu, Aug 31, 2017 at 12:57:29PM -0700, Darrick J. Wong wrote:
> TBH I like this less because now the responsibility for checking valid
> inputs is split between xfs_ioctl_setattr_xflags and xfs_set_diflags.
> I'd rather increase the function count by one than morph the setting
> function into check-and-set.

I'm not worried about the function count - I'm worried about duplicating
the information of which flags are stored in di_flags2.  With this patch
we have one point where we can naturally check this.  In your patch
we need another define that needs to be kept uptodate.

If you are worried about the check and set we could move the set into
the caller, but to me that doesn't seem any cleaner.  Example attached
below:

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 9c0c7a920304..511cd7c830ab 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -931,16 +931,15 @@ xfs_ioc_fsgetxattr(
 	return 0;
 }
 
-STATIC void
-xfs_set_diflags(
+STATIC unsigned int
+xfs_flags2diflags(
 	struct xfs_inode	*ip,
 	unsigned int		xflags)
 {
-	unsigned int		di_flags;
-	uint64_t		di_flags2;
-
 	/* can't set PREALLOC this way, just preserve it */
-	di_flags = (ip->i_d.di_flags & XFS_DIFLAG_PREALLOC);
+	unsigned int		di_flags =
+		(ip->i_d.di_flags & XFS_DIFLAG_PREALLOC);
+
 	if (xflags & FS_XFLAG_IMMUTABLE)
 		di_flags |= XFS_DIFLAG_IMMUTABLE;
 	if (xflags & FS_XFLAG_APPEND)
@@ -970,19 +969,24 @@ xfs_set_diflags(
 		if (xflags & FS_XFLAG_EXTSIZE)
 			di_flags |= XFS_DIFLAG_EXTSIZE;
 	}
-	ip->i_d.di_flags = di_flags;
 
-	/* diflags2 only valid for v3 inodes. */
-	if (ip->i_d.di_version < 3)
-		return;
+	return di_flags;
+}
+
+STATIC uint64_t
+xfs_flags2diflags2(
+	struct xfs_inode	*ip,
+	unsigned int		xflags)
+{
+	uint64_t		di_flags2 =
+		(ip->i_d.di_flags2 & XFS_DIFLAG2_REFLINK);
 
-	di_flags2 = (ip->i_d.di_flags2 & XFS_DIFLAG2_REFLINK);
 	if (xflags & FS_XFLAG_DAX)
 		di_flags2 |= XFS_DIFLAG2_DAX;
 	if (xflags & FS_XFLAG_COWEXTSIZE)
 		di_flags2 |= XFS_DIFLAG2_COWEXTSIZE;
 
-	ip->i_d.di_flags2 = di_flags2;
+	return di_flags2;
 }
 
 STATIC void
@@ -1022,6 +1026,7 @@ xfs_ioctl_setattr_xflags(
 	struct fsxattr		*fa)
 {
 	struct xfs_mount	*mp = ip->i_mount;
+	uint64_t		di_flags2;
 
 	/* Can't change realtime flag if any extents are allocated. */
 	if ((ip->i_d.di_nextents || ip->i_delayed_blks) &&
@@ -1052,7 +1057,14 @@ xfs_ioctl_setattr_xflags(
 	    !capable(CAP_LINUX_IMMUTABLE))
 		return -EPERM;
 
-	xfs_set_diflags(ip, fa->fsx_xflags);
+	/* diflags2 only valid for v3 inodes. */
+	di_flags2 = xfs_flags2diflags(ip, fa->fsx_xflags);
+	if (di_flags2 && ip->i_d.di_version < 3)
+		return -EINVAL;
+
+	ip->i_d.di_flags = xfs_flags2diflags(ip, fa->fsx_xflags);
+	ip->i_d.di_flags2 = di_flags2;
+
 	xfs_diflags_to_linux(ip);
 	xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);
 	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);