Discard the whole device before starting to create the filesystem structures.
Modelled after similar support in mkfs.xfs.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: btrfs-progs-unstable/utils.c
===================================================================
--- btrfs-progs-unstable.orig/utils.c 2009-10-30 09:34:00.000000000 +0000
+++ btrfs-progs-unstable/utils.c 2009-10-30 09:38:01.000000000 +0000
@@ -46,6 +46,20 @@
static inline int ioctl(int fd, int define, u64 *size) { return 0; }
#endif
+#ifndef BLKDISCARD
+#define BLKDISCARD _IO(0x12,119)
+#endif
+
+static int
+discard_blocks(int fd, u64 start, u64 len)
+{
+ u64 range[2] = { start, len };
+
+ if (ioctl(fd, BLKDISCARD, &range) < 0)
+ return errno;
+ return 0;
+}
+
static u64 reference_root_table[] = {
[1] = BTRFS_ROOT_TREE_OBJECTID,
[2] = BTRFS_EXTENT_TREE_OBJECTID,
@@ -532,6 +546,13 @@ int btrfs_prepare_device(int fd, char *f
"(must be at least 256 MB)\n", file);
exit(1);
}
+
+ /*
+ * We intentionally ignore errors from the discard ioctl. It is
+ * not necessary for the mkfs functionality but just an optimization.
+ */
+ discard_blocks(fd, 0, block_count);
+
ret = zero_dev_start(fd);
if (ret) {
fprintf(stderr, "failed to zero device start %d\n", ret);
--
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