[PATCH] xfs_io: support a basic extent swap command

[Brian Foster <bfoster@redhat.com>]

Extent swap is a low level mechanism exported by XFS to facilitate
filesystem defragmentation. It is typically invoked by xfs_fsr under
conditions that will atomically adjust inode extent state without
loss of file data.

xfs_fsr does not provide the necessary controls for low-level
testing of the extent swap command, however. For example, xfs_fsr
implements policies that dictate when to perform an extent swap and
offers no control over the donor file characteristics.

Add a basic swapext command to xfs_io that allows userspace
invocation of the command under more controlled conditions. This
command makes no effort to retain data across the operation. As
such, it is primarily for testing purposes (i.e., in support of
xfstests, etc.).

Signed-off-by: Brian Foster <bfoster@redhat.com>
---

This command is in support of an xfstests test to be posted shortly...

Brian

 io/Makefile  |   3 +-
 io/init.c    |   1 +
 io/io.h      |   1 +
 io/swapext.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 111 insertions(+), 1 deletion(-)
 create mode 100644 io/swapext.c

diff --git a/io/Makefile b/io/Makefile
index 6725936d..2f9249e8 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -11,7 +11,8 @@ 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
+	pwrite.c reflink.c seek.c shutdown.c stat.c swapext.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 20d5f80d..2ade03f4 100644
--- a/io/init.c
+++ b/io/init.c
@@ -88,6 +88,7 @@ init_commands(void)
 	sendfile_init();
 	shutdown_init();
 	stat_init();
+	swapext_init();
 	sync_init();
 	sync_range_init();
 	truncate_init();
diff --git a/io/io.h b/io/io.h
index 3862985f..258311f1 100644
--- a/io/io.h
+++ b/io/io.h
@@ -118,6 +118,7 @@ extern void		quit_init(void);
 extern void		seek_init(void);
 extern void		shutdown_init(void);
 extern void		stat_init(void);
+extern void		swapext_init(void);
 extern void		sync_init(void);
 extern void		truncate_init(void);
 extern void		utimes_init(void);
diff --git a/io/swapext.c b/io/swapext.c
new file mode 100644
index 00000000..5e161d69
--- /dev/null
+++ b/io/swapext.c
@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2018 Red Hat, Inc.
+ * 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 "command.h"
+#include "input.h"
+#include "init.h"
+#include "io.h"
+
+static cmdinfo_t swapext_cmd;
+
+static void
+swapext_help(void)
+{
+	printf(_(
+"\n"
+" Swaps extents between the open file descriptor and the supplied filename.\n"
+"\n"));
+}
+
+static int
+xfs_bulkstat_single(
+	int			fd,
+	xfs_ino_t		*lastip,
+	struct xfs_bstat	*ubuffer)
+{
+	struct xfs_fsop_bulkreq	bulkreq;
+
+	bulkreq.lastip = (__u64 *)lastip;
+	bulkreq.icount = 1;
+	bulkreq.ubuffer = ubuffer;
+	bulkreq.ocount = NULL;
+	return ioctl(fd, XFS_IOC_FSBULKSTAT_SINGLE, &bulkreq);
+}
+
+static int
+swapext_f(
+	int			argc,
+	char			**argv)
+{
+	int			fd;
+	int			error;
+	struct xfs_swapext	sx;
+	struct stat		stat;
+
+	/* open the donor file */
+	fd = openfile(argv[1], NULL, 0, 0, NULL);
+	if (fd < 0)
+		return 0;
+
+	/*
+	 * stat the target file to get the inode number and use the latter to
+	 * get the bulkstat info for the swapext cmd.
+	 */
+	error = fstat(file->fd, &stat);
+	if (error) {
+		perror("fstat");
+		goto out;
+	}
+
+	error = xfs_bulkstat_single(file->fd, &stat.st_ino, &sx.sx_stat);
+	if (error) {
+		perror("bulkstat");
+		goto out;
+	}
+	sx.sx_version = XFS_SX_VERSION;
+	sx.sx_fdtarget = file->fd;
+	sx.sx_fdtmp = fd;
+	sx.sx_offset = 0;
+	sx.sx_length = stat.st_size;
+	error = ioctl(file->fd, XFS_IOC_SWAPEXT, &sx);
+	if (error)
+		perror("swapext");
+
+out:
+	close(fd);
+	return 0;
+}
+
+void
+swapext_init(void)
+{
+	swapext_cmd.name = "swapext";
+	swapext_cmd.cfunc = swapext_f;
+	swapext_cmd.argmin = 1;
+	swapext_cmd.argmax = 1;
+	swapext_cmd.flags = CMD_NOMAP_OK;
+	swapext_cmd.args = _("<donorfile>");
+	swapext_cmd.oneline = _("Swap extents between files.");
+	swapext_cmd.help = swapext_help;
+
+	add_command(&swapext_cmd);
+}
-- 
2.13.6