[PATCH v1 0/2] losetup: support direct-IO to backing file

[PATCH v1 0/2] losetup: support direct-IO to backing file

[Ming Lei]

Hi,

The loop direct I/O patches[1] have been merged to linus kernel tree
and will be released in v4.4.

So the two patches provide interfaces for using direct IO/AIO
in losetup.

 include/loopdev.h   |  4 ++++
 lib/loopdev.c       | 40 ++++++++++++++++++++++++++++++++++++++++
 sys-utils/losetup.c | 33 +++++++++++++++++++++++++++++++--
 3 files changed, 75 insertions(+), 2 deletions(-)


[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bc07c10a3603a5ab3ef01ba42b3d41f9ac63d1b6

V1:
	- support to set direct IO for 'new' device, such as 
		loseutp --direct-io 1 -f test.img


Thanks,
Ming

[PATCH v1 1/2] losetup: support ioctl cmd of LOOP_SET_DIRECT_IO

[Ming Lei]

>From v4.4, linux kernel starts to support direct I/O and
AIO to backing file for loop driver, so allow losetup to
enable the feature by using LOOP_SET_DIRECT_IO ioctl cmd.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 include/loopdev.h   |  2 ++
 lib/loopdev.c       | 18 ++++++++++++++++++
 sys-utils/losetup.c | 27 +++++++++++++++++++++++++--
 3 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/include/loopdev.h b/include/loopdev.h
index 573a569..9a7f6ba 100644
--- a/include/loopdev.h
+++ b/include/loopdev.h
@@ -23,6 +23,7 @@
 #define LOOP_GET_STATUS64	0x4C05
 /* #define LOOP_CHANGE_FD	0x4C06 */
 #define LOOP_SET_CAPACITY	0x4C07
+#define LOOP_SET_DIRECT_IO	0x4C08
 
 /* /dev/loop-control interface */
 #ifndef LOOP_CTL_ADD
@@ -164,6 +165,7 @@ extern int loopcxt_next(struct loopdev_cxt *lc);
 extern int loopcxt_setup_device(struct loopdev_cxt *lc);
 extern int loopcxt_delete_device(struct loopdev_cxt *lc);
 extern int loopcxt_set_capacity(struct loopdev_cxt *lc);
+extern int loopcxt_set_dio(struct loopdev_cxt *lc, unsigned long use_dio);
 
 int loopcxt_set_offset(struct loopdev_cxt *lc, uint64_t offset);
 int loopcxt_set_sizelimit(struct loopdev_cxt *lc, uint64_t sizelimit);
diff --git a/lib/loopdev.c b/lib/loopdev.c
index fe047cd..ff99dd4 100644
--- a/lib/loopdev.c
+++ b/lib/loopdev.c
@@ -1315,6 +1315,24 @@ int loopcxt_set_capacity(struct loopdev_cxt *lc)
 	return 0;
 }
 
+int loopcxt_set_dio(struct loopdev_cxt *lc, unsigned long use_dio)
+{
+	int fd = loopcxt_get_fd(lc);
+
+	if (fd < 0)
+		return -EINVAL;
+
+	/* Kernels prior to v4.4 don't support this ioctl */
+	if (ioctl(fd, LOOP_SET_DIRECT_IO, use_dio) < 0) {
+		int rc = -errno;
+		DBG(CXT, ul_debugobj(lc, "LOOP_SET_DIRECT_IO failed: %m"));
+		return rc;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "direct io set"));
+	return 0;
+}
+
 int loopcxt_delete_device(struct loopdev_cxt *lc)
 {
 	int fd = loopcxt_get_fd(lc);
diff --git a/sys-utils/losetup.c b/sys-utils/losetup.c
index a68b222..68f7777 100644
--- a/sys-utils/losetup.c
+++ b/sys-utils/losetup.c
@@ -35,6 +35,7 @@ enum {
 	A_SHOW_ONE,		/* print info about one device */
 	A_FIND_FREE,		/* find first unused */
 	A_SET_CAPACITY,		/* set device capacity */
+	A_SET_DIRECT_IO,	/* set accessing backing file by direct io */
 };
 
 enum {
@@ -393,6 +394,7 @@ static void usage(FILE *out)
 	fputs(_("     --sizelimit <num>         device is limited to <num> bytes of the file\n"), out);
 	fputs(_(" -P, --partscan                create a partitioned loop device\n"), out);
 	fputs(_(" -r, --read-only               set up a read-only loop device\n"), out);
+	fputs(_("     --direct-io               open backing file with O_DIRECT\n"), out);
 	fputs(_("     --show                    print device name after setup (with -f)\n"), out);
 	fputs(_(" -v, --verbose                 verbose mode\n"), out);
 
@@ -446,11 +448,13 @@ int main(int argc, char **argv)
 	int res = 0, showdev = 0, lo_flags = 0;
 	char *outarg = NULL;
 	int list = 0;
+	unsigned long use_dio = 0, set_dio = 0;
 
 	enum {
 		OPT_SIZELIMIT = CHAR_MAX + 1,
 		OPT_SHOW,
-		OPT_RAW
+		OPT_RAW,
+		OPT_DIO
 	};
 	static const struct option longopts[] = {
 		{ "all", 0, 0, 'a' },
@@ -468,6 +472,7 @@ int main(int argc, char **argv)
 		{ "sizelimit", 1, 0, OPT_SIZELIMIT },
 		{ "partscan", 0, 0, 'P' },
 		{ "read-only", 0, 0, 'r' },
+		{ "direct-io", 1, 0, OPT_DIO },
 		{ "raw", 0, 0, OPT_RAW },
 		{ "show", 0, 0, OPT_SHOW },
 		{ "verbose", 0, 0, 'v' },
@@ -557,6 +562,10 @@ int main(int argc, char **argv)
 		case OPT_SHOW:
 			showdev = 1;
 			break;
+		case OPT_DIO:
+			set_dio = 1;
+			use_dio = strtoul_or_err(optarg, _("failed to parse dio"));
+			break;
 		case 'v':
 			break;
 		case 'V':
@@ -609,8 +618,13 @@ int main(int argc, char **argv)
 	if (!act && optind + 1 == argc) {
 		/*
 		 * losetup [--list] <device>
+		 * OR
+		 * losetup --direct-io DIO <device>
 		 */
-		act = A_SHOW_ONE;
+		if (!set_dio)
+			act = A_SHOW_ONE;
+		else
+			act = A_SET_DIRECT_IO;
 		if (!is_loopdev(argv[optind]) ||
 		    loopcxt_set_device(&lc, argv[optind]))
 			err(EXIT_FAILURE, _("%s: failed to use device"),
@@ -695,6 +709,8 @@ int main(int argc, char **argv)
 			if (showdev)
 				printf("%s\n", loopcxt_get_device(&lc));
 			warn_size(file, sizelimit);
+			if (set_dio)
+				goto lo_set_dio;
 		}
 		break;
 	}
@@ -747,6 +763,13 @@ int main(int argc, char **argv)
 			warn(_("%s: set capacity failed"),
 			        loopcxt_get_device(&lc));
 		break;
+	case A_SET_DIRECT_IO:
+ lo_set_dio:
+		res = loopcxt_set_dio(&lc, use_dio);
+		if (res)
+			warn(_("%s: set direct io failed"),
+			        loopcxt_get_device(&lc));
+		break;
 	default:
 		usage(stderr);
 		break;
-- 
1.9.1

[PATCH v1 2/2] losetup: support list direct io

[Ming Lei]

So that user can see if DIO is set for current loop device.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 include/loopdev.h   |  2 ++
 lib/loopdev.c       | 22 ++++++++++++++++++++++
 sys-utils/losetup.c |  6 ++++++
 3 files changed, 30 insertions(+)

diff --git a/include/loopdev.h b/include/loopdev.h
index 9a7f6ba..18ca41f 100644
--- a/include/loopdev.h
+++ b/include/loopdev.h
@@ -40,6 +40,7 @@ enum {
 	LO_FLAGS_USE_AOPS   = 2,
 	LO_FLAGS_AUTOCLEAR  = 4,	/* kernel >= 2.6.25 */
 	LO_FLAGS_PARTSCAN   = 8,	/* kernel >= 3.2 */
+	LO_FLAGS_DIRECT_IO  = 16,	/* kernel >= 4.2 */
 };
 
 #define LO_NAME_SIZE	64
@@ -181,6 +182,7 @@ extern int loopcxt_get_encrypt_type(struct loopdev_cxt *lc, uint32_t *type);
 extern const char *loopcxt_get_crypt_name(struct loopdev_cxt *lc);
 extern int loopcxt_is_autoclear(struct loopdev_cxt *lc);
 extern int loopcxt_is_readonly(struct loopdev_cxt *lc);
+extern int loopcxt_is_dio(struct loopdev_cxt *lc);
 extern int loopcxt_is_partscan(struct loopdev_cxt *lc);
 extern int loopcxt_find_by_backing_file(struct loopdev_cxt *lc,
 				const char *filename,
diff --git a/lib/loopdev.c b/lib/loopdev.c
index ff99dd4..54c6200 100644
--- a/lib/loopdev.c
+++ b/lib/loopdev.c
@@ -955,6 +955,28 @@ int loopcxt_is_readonly(struct loopdev_cxt *lc)
 
 /*
  * @lc: context
+ *
+ * Returns: 1 if the dio flags is set.
+ */
+int loopcxt_is_dio(struct loopdev_cxt *lc)
+{
+	struct sysfs_cxt *sysfs = loopcxt_get_sysfs(lc);
+
+	if (sysfs) {
+		int fl;
+		if (sysfs_read_int(sysfs, "loop/dio", &fl) == 0)
+			return fl;
+	}
+	if (loopcxt_ioctl_enabled(lc)) {
+		struct loop_info64 *lo = loopcxt_get_info(lc);
+		if (lo)
+			return lo->lo_flags & LO_FLAGS_DIRECT_IO;
+	}
+	return 0;
+}
+
+/*
+ * @lc: context
  * @st: backing file stat or NULL
  * @backing_file: filename
  * @offset: offset
diff --git a/sys-utils/losetup.c b/sys-utils/losetup.c
index 68f7777..918c34d 100644
--- a/sys-utils/losetup.c
+++ b/sys-utils/losetup.c
@@ -49,6 +49,7 @@ enum {
 	COL_PARTSCAN,
 	COL_RO,
 	COL_SIZELIMIT,
+	COL_DIO,
 };
 
 /* basic output flags */
@@ -74,6 +75,7 @@ static struct colinfo infos[] = {
 	[COL_RO]          = { "RO",           1, SCOLS_FL_RIGHT, N_("read-only device")},
 	[COL_SIZELIMIT]   = { "SIZELIMIT",    5, SCOLS_FL_RIGHT, N_("size limit of the file in bytes")},
 	[COL_MAJMIN]      = { "MAJ:MIN",      3, 0, N_("loop device major:minor number")},
+	[COL_DIO]         = { "DIO",          1, SCOLS_FL_RIGHT, N_("access backing file with direct-io")},
 };
 
 static int columns[ARRAY_SIZE(infos) * 2] = {-1};
@@ -271,6 +273,9 @@ static int set_scols_data(struct loopdev_cxt *lc, struct libscols_line *ln)
 		case COL_RO:
 			p = loopcxt_is_readonly(lc) ? "1" : "0";
 			break;
+		case COL_DIO:
+			p = loopcxt_is_dio(lc) ? "1" : "0";
+			break;
 		case COL_PARTSCAN:
 			p = loopcxt_is_partscan(lc) ? "1" : "0";
 			break;
@@ -599,6 +604,7 @@ int main(int argc, char **argv)
 		columns[ncolumns++] = COL_AUTOCLR;
 		columns[ncolumns++] = COL_RO;
 		columns[ncolumns++] = COL_BACK_FILE;
+		columns[ncolumns++] = COL_DIO;
 	}
 
 	if (act == A_FIND_FREE && optind < argc) {
-- 
1.9.1

Re: [PATCH v1 0/2] losetup: support direct-IO to backing file

[Karel Zak]

On Tue, Nov 17, 2015 at 10:32:46PM +0800, Ming Lei wrote:
>  include/loopdev.h   |  4 ++++
>  lib/loopdev.c       | 40 ++++++++++++++++++++++++++++++++++++++++
>  sys-utils/losetup.c | 33 +++++++++++++++++++++++++++++++--
>  3 files changed, 75 insertions(+), 2 deletions(-)
> 
> 
> [1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bc07c10a3603a5ab3ef01ba42b3d41f9ac63d1b6
> 
> V1:
> 	- support to set direct IO for 'new' device, such as 
> 		loseutp --direct-io 1 -f test.img

Applied, thanks!

I have a little bit changed the command line option to:

    --direct-io[=on|off]

where the default is "on", so you can use:

    losetup -f --direct-io file.img

to enable direct-io, to disable you have to use:

    losetup --direct-io=off /dev/loop0

I guess the most common usage will be to enable direct I/O :-)


https://github.com/karelzak/util-linux/commit/f98d9641a371421640a8f1cfe497030758f86dca

    Karel


-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com