[PATCH] mkfs: warn about V4 deprecation when creating new V4 filesystems

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

The V4 filesystem format is deprecated in the upstream Linux kernel.  In
September 2025 it will be turned off by default in the kernel and five
years after that, support will be removed entirely.  Warn people
formatting new filesystems with the old format, particularly since V4 is
not the default.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 mkfs/xfs_mkfs.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index 53904677..b8c11ce9 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2103,6 +2103,15 @@ _("Directory ftype field always enabled on CRC enabled filesystems\n"));
 		}
 
 	} else {	/* !crcs_enabled */
+		/*
+		 * The V4 filesystem format is deprecated in the upstream Linux
+		 * kernel.  In September 2025 it will be turned off by default
+		 * in the kernel and in September 2030 support will be removed
+		 * entirely.
+		 */
+		fprintf(stdout,
+_("V4 filesystems are deprecated and will not be supported by future versions.\n"));
+
 		/*
 		 * The kernel doesn't support crc=0,finobt=1 filesystems.
 		 * If crcs are not enabled and the user has not explicitly