[PATCH 1/2] mkfs: Break block discard into chunks of 2 GB

[Pavel Reichl <preichl@redhat.com>]

Signed-off-by: Pavel Reichl <preichl@redhat.com>
---
 mkfs/xfs_mkfs.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index 18338a61..a02d6f66 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -1242,15 +1242,33 @@ done:
 static void
 discard_blocks(dev_t dev, uint64_t nsectors)
 {
-	int fd;
+	int		fd;
+	uint64_t	offset		= 0;
+	/* Maximal chunk of bytes to discard is 2GB */
+	const uint64_t	step		= (uint64_t)2<<30;
+	/* Sector size is 512 bytes */
+	const uint64_t	count		= nsectors << 9;
 
-	/*
-	 * We intentionally ignore errors from the discard ioctl.  It is
-	 * not necessary for the mkfs functionality but just an optimization.
-	 */
 	fd = libxfs_device_to_fd(dev);
-	if (fd > 0)
-		platform_discard_blocks(fd, 0, nsectors << 9);
+	if (fd <= 0)
+		return;
+
+	while (offset < count) {
+		uint64_t	tmp_step = step;
+
+		if ((offset + step) > count)
+			tmp_step = count - offset;
+
+		/*
+		 * We intentionally ignore errors from the discard ioctl. It is
+		 * not necessary for the mkfs functionality but just an
+		 * optimization. However we should stop on error.
+		 */
+		if (platform_discard_blocks(fd, offset, tmp_step))
+			return;
+
+		offset += tmp_step;
+	}
 }
 
 static __attribute__((noreturn)) void
-- 
2.23.0