[PATCH V2] Make btrfs_prepare_device parallel during mkfs.btrfs

[Li Zhang <zhanglikernel@gmail.com>]

[enhancement]
When a disk is formatted as btrfs, it calls
btrfs_prepare_device for each device, which takes too much time.

[implementation]
Put each btrfs_prepare_device into a thread,
wait for the first thread to complete to mkfs.btrfs,
and wait for other threads to complete before adding
other devices to the file system.

[test]
Using the btrfs-progs test case mkfs-tests, mkfs.btrfs works fine.

But I don't have an actual zoed device,
so I don't know how much time it saves, If you guys
have a way to test it, please let me know.

Signed-off-by: Li Zhang <zhanglikernel@gmail.com>
---
Issue: 496

V1:
* Put btrfs_prepare_device into threads and make them parallel

V2:
* Set the 4 variables used by btrfs_prepare_device as global variables.
* Use pthread_mutex to ensure error messages are not messed up.
* Correct the error message
* Wait for all threads to exit in a loop

 mkfs/main.c | 132 +++++++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 95 insertions(+), 37 deletions(-)

diff --git a/mkfs/main.c b/mkfs/main.c
index ce096d3..b111f12 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -31,6 +31,7 @@
 #include <uuid/uuid.h>
 #include <ctype.h>
 #include <blkid/blkid.h>
+#include <pthread.h>
 #include "kernel-shared/ctree.h"
 #include "kernel-shared/disk-io.h"
 #include "kernel-shared/free-space-tree.h"
@@ -60,6 +61,20 @@ struct mkfs_allocation {
 	u64 system;
 };
 
+static bool zero_end;
+static bool discard;
+static bool zoned;
+static int oflags;
+
+static pthread_mutex_t prepare_mutex;
+
+struct prepare_device_progress {
+	char *file;
+	u64 dev_block_count;
+	u64 block_count;
+	int ret;
+};
+
 static int create_metadata_block_groups(struct btrfs_root *root, bool mixed,
 				struct mkfs_allocation *allocation)
 {
@@ -969,6 +984,30 @@ fail:
 	return ret;
 }
 
+static void *prepare_one_dev(void *ctx)
+{
+	struct prepare_device_progress *prepare_ctx = ctx;
+	int fd;
+
+	fd = open(prepare_ctx->file, oflags);
+	if (fd < 0) {
+		pthread_mutex_lock(&prepare_mutex);
+		error("unable to open %s: %m", prepare_ctx->file);
+		pthread_mutex_unlock(&prepare_mutex);
+		prepare_ctx->ret = fd;
+		return NULL;
+	}
+	prepare_ctx->ret = btrfs_prepare_device(fd,
+		prepare_ctx->file, &prepare_ctx->dev_block_count,
+		prepare_ctx->block_count,
+		(bconf.verbose ? PREP_DEVICE_VERBOSE : 0) |
+		(zero_end ? PREP_DEVICE_ZERO_END : 0) |
+		(discard ? PREP_DEVICE_DISCARD : 0) |
+		(zoned ? PREP_DEVICE_ZONED : 0));
+	close(fd);
+	return NULL;
+}
+
 int BOX_MAIN(mkfs)(int argc, char **argv)
 {
 	char *file;
@@ -984,7 +1023,7 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 	u32 nodesize = 0;
 	u32 sectorsize = 0;
 	u32 stripesize = 4096;
-	bool zero_end = true;
+	zero_end = true;
 	int fd = -1;
 	int ret = 0;
 	int close_ret;
@@ -993,11 +1032,10 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 	bool nodesize_forced = false;
 	bool data_profile_opt = false;
 	bool metadata_profile_opt = false;
-	bool discard = true;
+	discard = true;
 	bool ssd = false;
-	bool zoned = false;
+	zoned = false;
 	bool force_overwrite = false;
-	int oflags;
 	char *source_dir = NULL;
 	bool source_dir_set = false;
 	bool shrink_rootdir = false;
@@ -1006,6 +1044,8 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 	u64 shrink_size;
 	int dev_cnt = 0;
 	int saved_optind;
+	pthread_t *t_prepare = NULL;
+	struct prepare_device_progress *prepare_ctx = NULL;
 	char fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
 	u64 features = BTRFS_MKFS_DEFAULT_FEATURES;
 	u64 runtime_features = BTRFS_MKFS_DEFAULT_RUNTIME_FEATURES;
@@ -1428,29 +1468,49 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 		goto error;
 	}
 
-	dev_cnt--;
+	t_prepare = calloc(dev_cnt, sizeof(*t_prepare));
+	prepare_ctx = calloc(dev_cnt, sizeof(*prepare_ctx));
+
+	if (!t_prepare || !prepare_ctx) {
+		error("unable to alloc thread for preparing dev");
+		goto error;
+	}
 
+	pthread_mutex_init(&prepare_mutex, NULL);
+	zero_end = zero_end;
+	discard = discard;
+	zoned = zoned;
 	oflags = O_RDWR;
-	if (zoned && zoned_model(file) == ZONED_HOST_MANAGED)
-		oflags |= O_DIRECT;
+	for (i = 0; i < dev_cnt; i++) {
+		if (zoned && zoned_model(argv[optind + i - 1]) ==
+			ZONED_HOST_MANAGED) {
+			oflags |= O_DIRECT;
+			break;
+		}
+	}
+	for (i = 0; i < dev_cnt; i++) {
+		prepare_ctx[i].file = argv[optind + i - 1];
+		prepare_ctx[i].block_count = block_count;
+		prepare_ctx[i].dev_block_count = block_count;
+		ret = pthread_create(&t_prepare[i], NULL,
+			prepare_one_dev, &prepare_ctx[i]);
+		if (ret) {
+			error("create thread for prepare devices failed, errno:%d", ret);
+			goto error;
+		}
+	}
+	for (i = 0; i < dev_cnt; i++)
+		pthread_join(t_prepare[i], NULL);
+	ret = prepare_ctx[0].ret;
 
-	/*
-	 * Open without O_EXCL so that the problem should not occur by the
-	 * following operation in kernel:
-	 * (btrfs_register_one_device() fails if O_EXCL is on)
-	 */
-	fd = open(file, oflags);
-	if (fd < 0) {
-		error("unable to open %s: %m", file);
+	if (ret) {
+		error("unable prepare device:%s.\n", prepare_ctx[0].file);
 		goto error;
 	}
-	ret = btrfs_prepare_device(fd, file, &dev_block_count, block_count,
-			(zero_end ? PREP_DEVICE_ZERO_END : 0) |
-			(discard ? PREP_DEVICE_DISCARD : 0) |
-			(bconf.verbose ? PREP_DEVICE_VERBOSE : 0) |
-			(zoned ? PREP_DEVICE_ZONED : 0));
-	if (ret)
-		goto error;
+
+	dev_cnt--;
+	fd = open(file, oflags);
+	dev_block_count = prepare_ctx[0].dev_block_count;
 	if (block_count && block_count > dev_block_count) {
 		error("%s is smaller than requested size, expected %llu, found %llu",
 		      file, (unsigned long long)block_count,
@@ -1459,7 +1519,7 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 	}
 
 	/* To create the first block group and chunk 0 in make_btrfs */
-	system_group_size = zoned ?  zone_size(file) : BTRFS_MKFS_SYSTEM_GROUP_SIZE;
+	system_group_size = zoned ? zone_size(file) : BTRFS_MKFS_SYSTEM_GROUP_SIZE;
 	if (dev_block_count < system_group_size) {
 		error("device is too small to make filesystem, must be at least %llu",
 				(unsigned long long)system_group_size);
@@ -1558,14 +1618,10 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 		goto raid_groups;
 
 	while (dev_cnt-- > 0) {
+		int dev_index = argc - saved_optind - dev_cnt - 1;
 		file = argv[optind++];
 
-		/*
-		 * open without O_EXCL so that the problem should not
-		 * occur by the following processing.
-		 * (btrfs_register_one_device() fails if O_EXCL is on)
-		 */
-		fd = open(file, O_RDWR);
+		fd = open(file, oflags);
 		if (fd < 0) {
 			error("unable to open %s: %m", file);
 			goto error;
@@ -1578,13 +1634,11 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 			close(fd);
 			continue;
 		}
-		ret = btrfs_prepare_device(fd, file, &dev_block_count,
-				block_count,
-				(bconf.verbose ? PREP_DEVICE_VERBOSE : 0) |
-				(zero_end ? PREP_DEVICE_ZERO_END : 0) |
-				(discard ? PREP_DEVICE_DISCARD : 0) |
-				(zoned ? PREP_DEVICE_ZONED : 0));
-		if (ret) {
+		dev_block_count = prepare_ctx[dev_index]
+			.dev_block_count;
+
+		if (prepare_ctx[dev_index].ret) {
+			error("unable prepare device:%s.\n", prepare_ctx[dev_index].file);
 			goto error;
 		}
 
@@ -1763,12 +1817,16 @@ out:
 
 	btrfs_close_all_devices();
 	free(label);
-
+	free(t_prepare);
+	free(prepare_ctx);
 	return !!ret;
+
 error:
 	if (fd > 0)
 		close(fd);
 
+	free(t_prepare);
+	free(prepare_ctx);
 	free(label);
 	exit(1);
 success:
-- 
1.8.3.1