From e8c85bb806084037a48bedb0613be9c1bb43d853 Mon Sep 17 00:00:00 2001
From: Kent Overstreet <koverstreet@google.com>
Date: Sun, 31 Jul 2011 19:29:22 -0700
Subject: [PATCH] Add a --writeback switch to make-bcache

---
 bcache.h      | 12 ++++++++++++
 make-bcache.c | 19 +++++++++++++++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/bcache.h b/bcache.h
index d91b3e18..e667cc01 100644
--- a/bcache.h
+++ b/bcache.h
@@ -1,6 +1,16 @@
 #ifndef _BCACHE_H
 #define _BCACHE_H
 
+#define BITMASK(name, type, field, offset, size)		\
+static inline uint64_t name(const type *k)			\
+{ return (k->field >> offset) & ~(((uint64_t) ~0) << size); }	\
+								\
+static inline void SET_##name(type *k, uint64_t v)		\
+{								\
+	k->field &= ~(~((uint64_t) ~0 << size) << offset);	\
+	k->field |= v << offset;				\
+}
+
 static const char bcache_magic[] = {
 	0xc6, 0x85, 0x73, 0xf6, 0x4e, 0x1a, 0x45, 0xca,
 	0x82, 0x65, 0xf5, 0x7f, 0x48, 0xba, 0x6d, 0x81 };
@@ -41,6 +51,8 @@ struct cache_sb {
 	uint64_t		d[];		/* journal buckets */
 };
 
+BITMASK(BDEV_WRITEBACK,	struct cache_sb, flags, 0, 1);
+
 inline uint64_t crc64(const void *_data, size_t len);
 
 #define node(i, j)		((void *) ((i)->d + (j)))
diff --git a/make-bcache.c b/make-bcache.c
index 58fe6744..d442853a 100644
--- a/make-bcache.c
+++ b/make-bcache.c
@@ -5,6 +5,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <getopt.h>
 #include <linux/fs.h>
 #include <stdbool.h>
 #include <stdint.h>
@@ -67,10 +68,16 @@ void usage()
 	       "	-b bucket size\n"
 	       "	-w block size (hard sector size of SSD, often 2k)\n"
 	       "	-U UUID\n"
-	       "	-S Set UUID\n");
+	       "	--writeback Enable writeback\n");
 	exit(EXIT_FAILURE);
 }
 
+int writeback;
+
+struct option opts[2] = {
+	{ "writeback", 0, &writeback, 1 }
+};
+
 void write_sb(char *dev, struct cache_sb *sb)
 {
 	int fd;
@@ -97,6 +104,12 @@ void write_sb(char *dev, struct cache_sb *sb)
 		exit(EXIT_FAILURE);
 	}
 
+	if (sb->version == CACHE_BACKING_DEV &&
+	    writeback)
+		SET_BDEV_WRITEBACK(sb, 1);
+	else
+		SET_BDEV_WRITEBACK(sb, 0);
+
 	sb->offset		= SB_SECTOR;
 	memcpy(sb->magic, bcache_magic, 16);
 	sb->nbuckets		= getblocks(fd) / sb->bucket_size;
@@ -153,7 +166,9 @@ int main(int argc, char **argv)
 	uuid_generate(sb.uuid);
 	uuid_generate(sb.set_uuid);
 
-	while ((c = getopt(argc, argv, "-CBU:w:b:")) != -1)
+	while ((c = getopt_long(argc, argv,
+				"-CBU:w:b:",
+				opts, NULL)) != -1)
 		switch (c) {
 		case 'C':
 			sb.version = 0;