lib,loopdev: add LOOP_CTL_GET_FREE support

Signed-off-by: Karel Zak <kzak@redhat.com>

3 files changed, 40 insertions, 8 deletions

diff --git a/include/loopdev.h b/include/loopdev.h
index 2c8db17f8..e675dab91 100644
--- a/include/loopdev.h
+++ b/include/loopdev.h
@@ -24,6 +24,13 @@
 /* #define LOOP_CHANGE_FD	0x4C06 */
 #define LOOP_SET_CAPACITY	0x4C07
 
+/* /dev/loop-control interface */
+#ifndef LOOP_CTL_ADD
+# define LOOP_CTL_ADD		0x4C80
+# define LOOP_CTL_REMOVE	0x4C81
+# define LOOP_CTL_GET_FREE	0x4C82
+#endif
+
 /*
  * loop_info.lo_flags
  */
@@ -104,7 +111,8 @@ enum {
 	LOOPDEV_FL_OFFSET	= (1 << 4),
 	LOOPDEV_FL_NOSYSFS	= (1 << 5),
 	LOOPDEV_FL_NOIOCTL	= (1 << 6),
-	LOOPDEV_FL_DEVSUBDIR	= (1 << 7)
+	LOOPDEV_FL_DEVSUBDIR	= (1 << 7),
+	LOOPDEV_FL_CONTROL	= (1 << 8),	/* system with /dev/loop-control */
 };
 
 /*
diff --git a/include/pathnames.h b/include/pathnames.h
index 07912bc59..e6e3d1957 100644
--- a/include/pathnames.h
+++ b/include/pathnames.h
@@ -121,8 +121,10 @@
 #endif
 
 #define _PATH_DEV_LOOP		"/dev/loop"
+#define _PATH_DEV_LOOPCTL	"/dev/loop-control"
 #define _PATH_DEV_TTY		"/dev/tty"
 
+
 /* udev paths */
 #define _PATH_DEV_BYLABEL	"/dev/disk/by-label"
 #define _PATH_DEV_BYUUID	"/dev/disk/by-uuid"
diff --git a/lib/loopdev.c b/lib/loopdev.c
index f83a443a0..3dfa78a40 100644
--- a/lib/loopdev.c
+++ b/lib/loopdev.c
@@ -139,6 +139,8 @@ int loopcxt_set_device(struct loopdev_cxt *lc, const char *device)
  */
 int loopcxt_init(struct loopdev_cxt *lc, int flags)
 {
+	struct stat st;
+
 	if (!lc)
 		return -EINVAL;
 
@@ -153,6 +155,9 @@ int loopcxt_init(struct loopdev_cxt *lc, int flags)
 		 */
 		lc->flags |= LOOPDEV_FL_NOIOCTL;
 
+	if (!(lc->flags & LOOPDEV_FL_CONTROL) && !stat(_PATH_DEV_LOOPCTL, &st))
+		lc->flags |= LOOPDEV_FL_CONTROL;
+
 	return 0;
 }
 
@@ -917,18 +922,35 @@ int loopcxt_delete_device(struct loopdev_cxt *lc)
 
 int loopcxt_find_unused(struct loopdev_cxt *lc)
 {
-	int rc;
+	int rc = -1;
 
 	DBG(lc, loopdev_debug("find_unused requested"));
 
-	rc = loopcxt_init_iterator(lc, LOOPITER_FL_FREE);
-	if (rc)
-		return rc;
+	if (lc->flags & LOOPDEV_FL_CONTROL) {
+		int ctl = open(_PATH_DEV_LOOPCTL, O_RDWR);
 
-	rc = loopcxt_next(lc);
-	loopcxt_deinit_iterator(lc);
+		if (ctl >= 0)
+			rc = ioctl(ctl, LOOP_CTL_GET_FREE);
+		if (rc >= 0) {
+			char name[16];
+			snprintf(name, sizeof(name), "loop%d", rc);
+
+			rc = loopiter_set_device(lc, name);
+		}
+		if (ctl >= 0)
+			close(ctl);
+		DBG(lc, loopdev_debug("find_unused by loop-control [rc=%d]", rc));
+	}
 
-	DBG(lc, loopdev_debug("find_unused done [rc=%d]", rc));
+	if (rc < 0) {
+		rc = loopcxt_init_iterator(lc, LOOPITER_FL_FREE);
+		if (rc)
+			return rc;
+
+		rc = loopcxt_next(lc);
+		loopcxt_deinit_iterator(lc);
+		DBG(lc, loopdev_debug("find_unused by scan [rc=%d]", rc));
+	}
 	return rc;
 }