[xfsprogs PATCH 2/2] xfs_io: add a new 'log_writes' command

[Ross Zwisler <ross.zwisler@linux.intel.com>]

Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
log marks via the external 'dmsetup' executable.  It's helpful to allow
users of xfs_io to adds these marks from within xfs_io instead of waiting
until after xfs_io exits because then they are able to replay the
dm-log-writes log up to immediately after another xfs_io operation such as
mwrite.  This isolates the log replay from other operations that happen as
part of xfs_io exiting (file handles being closed, mmaps being torn down,
etc.).  This also allows users to insert multiple marks between different
xfs_io commands.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Dave Chinner <david@fromorbit.com>
---
 io/Makefile       |  5 ++--
 io/init.c         |  1 +
 io/io.h           |  1 +
 io/log_writes.c   | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 man/man8/xfs_io.8 | 19 ++++++++++++++
 5 files changed, 102 insertions(+), 2 deletions(-)
 create mode 100644 io/log_writes.c

diff --git a/io/Makefile b/io/Makefile
index 050d6bd..51b2eae 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -10,8 +10,9 @@ LSRCFILES = xfs_bmap.sh xfs_freeze.sh xfs_mkfile.sh
 HFILES = init.h io.h
 CFILES = init.c \
 	attr.c bmap.c cowextsize.c encrypt.c file.c freeze.c fsync.c \
-	getrusage.c imap.c link.c mmap.c open.c parent.c pread.c prealloc.c \
-	pwrite.c reflink.c seek.c shutdown.c stat.c sync.c truncate.c utimes.c
+	getrusage.c imap.c link.c log_writes.c mmap.c open.c parent.c pread.c \
+	prealloc.c pwrite.c reflink.c seek.c shutdown.c stat.c sync.c \
+	truncate.c utimes.c
 
 LLDLIBS = $(LIBXCMD) $(LIBHANDLE) $(LIBPTHREAD)
 LTDEPENDENCIES = $(LIBXCMD) $(LIBHANDLE)
diff --git a/io/init.c b/io/init.c
index 20d5f80..34d87b5 100644
--- a/io/init.c
+++ b/io/init.c
@@ -72,6 +72,7 @@ init_commands(void)
 	help_init();
 	imap_init();
 	inject_init();
+	log_writes_init();
 	madvise_init();
 	mincore_init();
 	mmap_init();
diff --git a/io/io.h b/io/io.h
index 8b2753b..d62034a 100644
--- a/io/io.h
+++ b/io/io.h
@@ -109,6 +109,7 @@ extern void		getrusage_init(void);
 extern void		help_init(void);
 extern void		imap_init(void);
 extern void		inject_init(void);
+extern void		log_writes_init(void);
 extern void		mmap_init(void);
 extern void		open_init(void);
 extern void		parent_init(void);
diff --git a/io/log_writes.c b/io/log_writes.c
new file mode 100644
index 0000000..bc3952c
--- /dev/null
+++ b/io/log_writes.c
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2017 Intel Corporation.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include "platform_defs.h"
+#include "command.h"
+#include "init.h"
+
+static cmdinfo_t log_writes_cmd;
+
+static int
+mark_log(char *device, char *mark)
+{
+	char command[256];
+
+	snprintf(command, 256, "dmsetup message %s 0 mark %s",
+			device, mark);
+
+	return system(command);
+}
+
+static int
+log_writes_f(
+	int			argc,
+	char			**argv)
+{
+	char *device = NULL;
+	char *mark = NULL;
+	int c;
+
+	while ((c = getopt(argc, argv, "d:m:")) != EOF) {
+		switch (c) {
+		case 'd':
+			device = optarg;
+			break;
+		case 'm':
+			mark = optarg;
+			break;
+		default:
+			return command_usage(&log_writes_cmd);
+		}
+	}
+
+	if (device == NULL || mark == NULL)
+		return command_usage(&log_writes_cmd);
+
+	return mark_log(device, mark);
+}
+
+void
+log_writes_init(void)
+{
+	log_writes_cmd.name = "log_writes";
+	log_writes_cmd.altname = "lw";
+	log_writes_cmd.cfunc = log_writes_f;
+	log_writes_cmd.flags = CMD_NOMAP_OK | CMD_NOFILE_OK | CMD_FOREIGN_OK;
+	log_writes_cmd.argmin = 0;
+	log_writes_cmd.argmax = -1;
+	log_writes_cmd.args = _("-d device -m mark");
+	log_writes_cmd.oneline =
+		_("uses dmsetup to interact with the dm-log-writes module");
+
+	add_command(&log_writes_cmd);
+}
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 1693f7f..f18af99 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -1123,7 +1123,25 @@ version of policy structure (numeric)
 .BR get_encpolicy
 On filesystems that support encryption, display the encryption policy of the
 current file.
+.RE
+.PD
+.TP
+.BI "log_writes \-d " device " \-m "  mark
+Use
+.B dmsetup
+to interact with the
+.B dm-log-writes
+kernel module.  Currently the only operation
+supported is the creation of a mark in the log by executing the shell command:
 
+.B dmsetup message <device> 0 mark <mark>
+.PD
+.RE
+.TP
+.B lw
+See the
+.B log_writes
+command.
 .SH SEE ALSO
 .BR mkfs.xfs (8),
 .BR xfsctl (3),
@@ -1142,3 +1160,4 @@ current file.
 .BR pread (2),
 .BR pwrite (2),
 .BR readdir (3).
+.BR dmsetup (8).
-- 
2.9.5