From 96422adb362222c774d1aca345bb5b66bf022dd4 Mon Sep 17 00:00:00 2001
From: Tomas Mudrunka <tomas.mudrunka@gmail.com>
Date: Fri, 12 Jan 2024 16:00:02 +0100
Subject: [PATCH] MDRAID superblock generator

---
 c/mdraid-gen/mdraid.c | 119 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 c/mdraid-gen/mdraid.c

diff --git a/c/mdraid-gen/mdraid.c b/c/mdraid-gen/mdraid.c
new file mode 100644
index 0000000..7c946ca
--- /dev/null
+++ b/c/mdraid-gen/mdraid.c
@@ -0,0 +1,119 @@
+/* MDRAID Superblock generator
+This should create valid mdraid superblock for raid1 with 1 device.
+It is still work in progress, but following seems to be recognized:
+
+make mdraid
+./mdraid > test.img
+mdadm --examine test.img
+
+*/
+
+//#include <cstddef>
+#include <string.h>
+#include <time.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <linux/raid/md_p.h>
+
+void random_uuid(__u8 *buf)
+{
+	__u32 r[4];
+	for (int i = 0; i < 4; i++)
+		r[i] = random();
+	memcpy(buf, r, 16);
+}
+
+static unsigned int calc_sb_1_csum(struct mdp_superblock_1 * sb)
+{
+	unsigned int disk_csum, csum;
+	unsigned long long newcsum;
+	int size = sizeof(*sb) + __le32_to_cpu(sb->max_dev)*2;
+	unsigned int *isuper = (unsigned int*)sb;
+
+/* make sure I can count... (needs include cstddef) */
+/*
+	if (offsetof(struct mdp_superblock_1,data_offset) != 128 ||
+	    offsetof(struct mdp_superblock_1, utime) != 192 ||
+	    sizeof(struct mdp_superblock_1) != 256) {
+		fprintf(stderr, "WARNING - superblock isn't sized correctly\n");
+	}
+*/
+
+	disk_csum = sb->sb_csum;
+	sb->sb_csum = 0;
+	newcsum = 0;
+	for (; size>=4; size -= 4 ) {
+		newcsum += __le32_to_cpu(*isuper);
+		isuper++;
+	}
+
+	if (size == 2)
+		newcsum += __le16_to_cpu(*(unsigned short*) isuper);
+
+	csum = (newcsum & 0xffffffff) + (newcsum >> 32);
+	sb->sb_csum = disk_csum;
+	return __cpu_to_le32(csum);
+}
+
+int main() {
+	srand(time(NULL)); //FIXME: Seed UUID properly
+
+	struct mdp_superblock_1 sb = {0};
+
+	/* constant array information - 128 bytes */
+	sb.magic = 0xa92b4efc;		/* MD_SB_MAGIC: 0xa92b4efc - little endian */
+	sb.major_version = 1;	/* 1 */
+	sb.feature_map = 0;	/* bit 0 set if 'bitmap_offset' is meaningful */
+	sb.pad0 = 0;		/* always set to 0 when writing */
+
+	//TODO: set these
+	random_uuid(sb.set_uuid);	/* user-space generated. U8[16]*/
+	memcpy(sb.set_name, "localhost:777", 6);	/* set and interpreted by user-space. CHAR[32] */
+	sb.ctime=0;		/* lo 40 bits are seconds, top 24 are microseconds or 0*/
+
+	sb.level=1;		/* -4 (multipath), -1 (linear), 0,1,4,5 */
+	sb.layout=2;		/* only for raid5 and raid10 currently */
+	sb.size;		/* used size of component devices, in 512byte sectors */
+
+	sb.chunksize=0;		/* in 512byte sectors - not used in raid 1 */
+	sb.raid_disks=1;
+	sb.bitmap_offset=0;	/* sectors after start of superblock that bitmap starts
+					 * NOTE: signed, so bitmap can be before superblock
+					 * only meaningful of feature_map[0] is set.
+					 */
+
+	/* constant this-device information - 64 bytes */
+	sb.data_offset=4096+sizeof(sb);	/* sector start of data, often 0 */
+	sb.data_size;	/* sectors in this device that can be used for data */
+	sb.super_offset=8;	/* sector start of this superblock */
+
+	sb.dev_number=0;	/* permanent identifier of this  device - not role in raid */
+	sb.cnt_corrected_read=0; /* number of read errors that were corrected by re-writing */
+	random_uuid(sb.device_uuid); /* user-space setable, ignored by kernel U8[16] */
+	sb.devflags=0;	/* per-device flags.  Only two defined...*/
+		//#define	WriteMostly1	1	/* mask for writemostly flag in above */
+		//#define	FailFast1	2	/* Should avoid retries and fixups and just fail */
+
+	/* array state information - 64 bytes */
+	sb.utime=0;		/* 40 bits second, 24 bits microseconds */
+	sb.events=0;		/* incremented when superblock updated */
+	sb.resync_offset=0;	/* data before this offset (from data_offset) known to be in sync */
+	sb.max_dev=1;	/* size of devs[] array to consider */
+	//__u8	pad3[64-32];	/* set to 0 when writing */
+
+	/* device state information. Indexed by dev_number.
+	 * 2 bytes per device
+	 * Note there are no per-device state flags. State information is rolled
+	 * into the 'roles' value.  If a device is spare or faulty, then it doesn't
+	 * have a meaningful role.
+	 */
+	//__le16	dev_roles[];	/* role in array, or 0xffff for a spare, or 0xfffe for faulty */
+
+
+	sb.sb_csum=calc_sb_1_csum(&sb);
+
+	//printf("Superblock\n");
+	for(int i=0;i<4096;i++) putc(0, stdout);
+	fwrite(&sb, sizeof(sb), 1, stdout);
+	for(int i=0;i<40960;i++) putc(0, stdout);
+}
-- 
2.30.2