On Thu, Oct 26, 2017 at 08:56:38AM +1100, Dave Chinner wrote:

On Wed, Oct 25, 2017 at 02:47:04PM -0600, Ross Zwisler wrote:

quoted

Add a test that exercises DAX's new MAP_SYNC flag.

This test creates a file and writes to it via an mmap(), but never syncs
via fsync/msync.  This process is tracked via dm-log-writes, then replayed.

If MAP_SYNC is working the dm-log-writes replay will show the test file
with 1MiB of on-media block allocations.  This is because each allocating
page fault included an implicit metadata sync.  If MAP_SYNC isn't working
(which you can test by fiddling with the parameters to mmap()) the file
will be smaller or missing entirely.

Note that dm-log-writes doesn't track the data that we write via the
mmap(), so we can't do any data integrity checking.  We can only verify
that the metadata writes for the page faults happened.

Signed-off-by: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>

.....

quoted

--- /dev/null
+++ b/src/t_map_sync.c

@@ -0,0 +1,92 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define MiB(a) ((a)*1024*1024)
+
+/*
+ * These two defines were added to the kernel via commits entitled
+ * "mm: Define MAP_SYNC and VM_SYNC flags" and
+ * "mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap
+ * flags", respectively.
+ */
+#ifndef MAP_SYNC
+#define MAP_SYNC 0x80000
+#endif
+
+#ifndef MAP_SHARED_VALIDATE
+#define MAP_SHARED_VALIDATE 0x3
+#endif

Autoconf rules for detecting supported functionality, please...

Yep, that's better.  As you've suggested down below I'm adding this
functionality to xfs_io instead, and I've added autoconf rules there.

quoted

+
+void err_exit(char *op)
+{
+	fprintf(stderr, "%s: %s\n", op, strerror(errno));
+	exit(1);
+}
+
+void mark_log(char *logwrites_name, char *mark_name)
+{
+	char command[256];
+
+	snprintf(command, 256, "dmsetup message %s 0 mark %s",
+			logwrites_name, mark_name);
+
+	if (system(command))
+		err_exit("mark_log");
+}
+
+int main(int argc, char *argv[])
+{
+	int page_size = getpagesize();
+	int len = MiB(1);
+	int i, fd, err;
+	char *data;
+
+	if (argc < 4) {
+		printf("Usage: %s <file> <logwrites_name> <mark_name>\n",
+				basename(argv[0]));
+		exit(0);
+	}
+
+	fd = open(argv[1], O_RDWR|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR);
+	if (fd < 0)
+		err_exit("fd");
+
+	ftruncate(fd, len);
+
+	data = mmap(NULL, len, PROT_READ|PROT_WRITE,
+			MAP_SHARED_VALIDATE|MAP_SYNC, fd, 0);
+	if (data == MAP_FAILED)
+		err_exit("mmap");

As I say to all these sorts of one-off test prgrams: please add the
new MAP_SYNC flag to xfs_io rather than writing a one-off
test program to set it and write some data.

And if we're going to be adding special custom tests just because
we need to insert dm-log marks, add that functionality to xfs_io,
too.

That way we can create complex custom dm logwrite tests without
needing one-off test programs for them all...

Yep, that was a better path.  I've got things working - need to clean up and
I'll send out soon.

quoted

+#! /bin/bash
+# FS QA Test No. 466
+#
+# Use md_log_writes to verify that MAP_SYNC actually syncs metadata during

dm_log_writes?

Fixed.

quoted

+# We should see $SCRATCH_MNT/test as having 1MiB in block allocations
+du -sh $SCRATCH_MNT/test | _filter_scratch | _filter_spaces

Perhaps stat -c %b $SCRATCH_MNT/test ?

Maybe, but doesn't the output of 'stat -c %b' depend on the block size the
filesystem is using?  I think to use stat I'd have to check both %b and %B,
and account for different block sizes, or do some shell math.  I think it may
be easier to just use du.

Thank you for the review, sorry for the delayed response.