[PATCH mdadm v3 5/7] mdadm: Add --write-zeros option for Create

[Logan Gunthorpe <logang@deltatee.com>]

Add the --write-zeros option for Create which will send a write zeros
request to all the disks before assembling the array. After zeroing
the array, the disks will be in a known clean state and the initial
sync may be skipped.

Writing zeroes is best used when there is a hardware offload method
to zero the data. But even still, zeroing can take several minutes on
a large device. Because of this, all disks are zeroed in parallel using
their own forked process and a message is printed to the user. The main
process will proceed only after all the zeroing processes have completed
successfully.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>

fixup! mdadm: Add --write-zeros option for Create
---
 Create.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ReadMe.c |  2 ++
 mdadm.c  |  9 ++++++
 mdadm.h  |  7 +++++
 4 files changed, 101 insertions(+)

diff --git a/Create.c b/Create.c
index 1e94b90b96bd..31bed3a37a90 100644
--- a/Create.c
+++ b/Create.c
@@ -26,6 +26,8 @@
 #include	"md_u.h"
 #include	"md_p.h"
 #include	<ctype.h>
+#include	<fcntl.h>
+#include	<sys/wait.h>
 
 static int round_size_and_verify(unsigned long long *size, int chunk)
 {
@@ -91,6 +93,73 @@ int default_layout(struct supertype *st, int level, int verbose)
 	return layout;
 }
 
+static pid_t write_zeroes_fork(int fd, struct shape *s, struct supertype *st,
+			       struct mddev_dev *dv)
+
+{
+	unsigned long long offset_bytes, size_bytes;
+	int ret = 0;
+	pid_t pid;
+
+	size_bytes = KIB_TO_BYTES(s->size);
+
+	/*
+	 * If size_bytes is zero, this is a zoned raid array where
+	 * each disk is of a different size and uses its full
+	 * disk. Thus zero the entire disk.
+	 */
+	if (!size_bytes && !get_dev_size(fd, dv->devname, &size_bytes))
+		return -1;
+
+	if (dv->data_offset != INVALID_SECTORS)
+		offset_bytes = SEC_TO_BYTES(dv->data_offset);
+	else
+		offset_bytes = SEC_TO_BYTES(st->data_offset);
+
+	pr_info("zeroing data from %lld to %lld on: %s\n",
+		offset_bytes, size_bytes, dv->devname);
+
+	pid = fork();
+	if (pid < 0) {
+		pr_err("Could not fork to zero disks: %m\n");
+		return pid;
+	} else if (pid != 0) {
+		return pid;
+	}
+
+	if (fallocate(fd, FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE,
+		      offset_bytes, size_bytes)) {
+		pr_err("zeroing %s failed: %m\n", dv->devname);
+		ret = 1;
+	}
+
+	exit(ret);
+}
+
+static int wait_for_zero_forks(struct mdinfo *info, int count)
+{
+	int wstatus, ret = 0, i;
+	bool waited = false;
+
+	for (i = 0; i < count; i++) {
+		if (!info[i].zero_pid)
+			continue;
+
+		waited = true;
+		waitpid(info[i].zero_pid, &wstatus, 0);
+
+		if (!WIFEXITED(wstatus) || WEXITSTATUS(wstatus))
+			ret = 1;
+	}
+
+	if (ret)
+		pr_err("zeroing failed!\n");
+	else if (waited)
+		pr_info("zeroing finished\n");
+
+	return ret;
+}
+
 static int add_disk_to_super(int mdfd, struct shape *s, struct context *c,
 		struct supertype *st, struct mddev_dev *dv,
 		struct mdinfo *info, int have_container, int major_num)
@@ -148,6 +217,14 @@ static int add_disk_to_super(int mdfd, struct shape *s, struct context *c,
 	}
 	st->ss->getinfo_super(st, info, NULL);
 
+	if (s->write_zeroes) {
+		info->zero_pid = write_zeroes_fork(fd, s, st, dv);
+		if (info->zero_pid <= 0) {
+			ioctl(mdfd, STOP_ARRAY, NULL);
+			return 1;
+		}
+	}
+
 	if (have_container && c->verbose > 0)
 		pr_err("Using %s for device %d\n",
 		       map_dev(info->disk.major, info->disk.minor, 0),
@@ -287,6 +364,10 @@ static int add_disks(int mdfd, struct mdinfo *info, struct shape *s,
 		}
 
 		if (pass == 1) {
+			ret = wait_for_zero_forks(infos, total_slots);
+			if (ret)
+				goto out;
+
 			ret = update_metadata(mdfd, s, st, map, info,
 					      chosen_name);
 			if (ret)
@@ -295,6 +376,8 @@ static int add_disks(int mdfd, struct mdinfo *info, struct shape *s,
 	}
 
 out:
+	if (ret)
+		wait_for_zero_forks(infos, total_slots);
 	free(infos);
 	return ret;
 }
diff --git a/ReadMe.c b/ReadMe.c
index 7f94847e9769..50913dabca40 100644
--- a/ReadMe.c
+++ b/ReadMe.c
@@ -138,6 +138,7 @@ struct option long_options[] = {
     {"size",	  1, 0, 'z'},
     {"auto",	  1, 0, Auto}, /* also for --assemble */
     {"assume-clean",0,0, AssumeClean },
+    {"write-zeroes",0,0, WriteZeroes },
     {"metadata",  1, 0, 'e'}, /* superblock format */
     {"bitmap",	  1, 0, Bitmap},
     {"bitmap-chunk", 1, 0, BitmapChunk},
@@ -390,6 +391,7 @@ char Help_create[] =
 "  --write-journal=      : Specify journal device for RAID-4/5/6 array\n"
 "  --consistency-policy= : Specify the policy that determines how the array\n"
 "                     -k : maintains consistency in case of unexpected shutdown.\n"
+"  --write-zeroes        : Write zeroes to the disks before creating. This will bypass initial sync.\n"
 "\n"
 ;
 
diff --git a/mdadm.c b/mdadm.c
index 972adb524dfb..141838bd394f 100644
--- a/mdadm.c
+++ b/mdadm.c
@@ -602,6 +602,10 @@ int main(int argc, char *argv[])
 			s.assume_clean = 1;
 			continue;
 
+		case O(CREATE, WriteZeroes):
+			s.write_zeroes = 1;
+			continue;
+
 		case O(GROW,'n'):
 		case O(CREATE,'n'):
 		case O(BUILD,'n'): /* number of raid disks */
@@ -1306,6 +1310,11 @@ int main(int argc, char *argv[])
 		}
 	}
 
+	if (s.write_zeroes && !s.assume_clean) {
+		pr_info("Disk zeroing requested, setting --assume-clean to skip resync\n");
+		s.assume_clean = 1;
+	}
+
 	if (!mode && devs_found) {
 		mode = MISC;
 		devmode = 'Q';
diff --git a/mdadm.h b/mdadm.h
index 1ab31564efef..c7e00195d8c8 100644
--- a/mdadm.h
+++ b/mdadm.h
@@ -273,6 +273,9 @@ static inline void __put_unaligned32(__u32 val, void *p)
 
 #define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
 
+#define KIB_TO_BYTES(x)	((x) << 10)
+#define SEC_TO_BYTES(x)	((x) << 9)
+
 extern const char Name[];
 
 struct md_bb_entry {
@@ -387,6 +390,8 @@ struct mdinfo {
 		ARRAY_UNKNOWN_STATE,
 	} array_state;
 	struct md_bb bb;
+
+	pid_t zero_pid;
 };
 
 struct createinfo {
@@ -433,6 +438,7 @@ extern char Version[], Usage[], Help[], OptionHelp[],
  */
 enum special_options {
 	AssumeClean = 300,
+	WriteZeroes,
 	BitmapChunk,
 	WriteBehind,
 	ReAdd,
@@ -593,6 +599,7 @@ struct shape {
 	int	bitmap_chunk;
 	char	*bitmap_file;
 	int	assume_clean;
+	bool	write_zeroes;
 	int	write_behind;
 	unsigned long long size;
 	unsigned long long data_offset;
-- 
2.30.2