dm: allow remove to be deferred

This patch allows the removal of an open device to be deferred until
it is closed.  (Previously such a removal attempt would fail.)

The deferred remove functionality is enabled by setting the flag
DM_DEFERRED_REMOVE in the ioctl structure on DM_DEV_REMOVE or
DM_REMOVE_ALL ioctl.

On return from DM_DEV_REMOVE, the flag DM_DEFERRED_REMOVE indicates if
the device was removed immediately or flagged to be removed on close -
if the flag is clear, the device was removed.

On return from DM_DEV_STATUS and other ioctls, the flag
DM_DEFERRED_REMOVE is set if the device is scheduled to be removed on
closure.

A device that is scheduled to be deleted can be revived using the
message "@cancel_deferred_remove". This message clears the
DMF_DEFERRED_REMOVE flag so that the device won't be deleted on close.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index f1e12bd40b3b..c8a4302093a3 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -267,9 +267,9 @@ enum {
 #define DM_DEV_SET_GEOMETRY     _IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR        4
-#define DM_VERSION_MINOR        26
+#define DM_VERSION_MINOR        27
 #define DM_VERSION_PATCHLEVEL   0
-#define DM_VERSION_EXTRA        "-ioctl (2013-08-15)"
+#define DM_VERSION_EXTRA        "-ioctl (2013-10-30)"
 
 /* Status bits */
 #define DM_READONLY_FLAG        (1 << 0) /* In/Out */
@@ -341,4 +341,15 @@ enum {
  */
 #define DM_DATA_OUT_FLAG                (1 << 16) /* Out */
 
+/*
+ * If set with DM_DEV_REMOVE or DM_REMOVE_ALL this indicates that if
+ * the device cannot be removed immediately because it is still in use
+ * it should instead be scheduled for removal when it gets closed.
+ *
+ * On return from DM_DEV_REMOVE, DM_DEV_STATUS or other ioctls, this
+ * flag indicates that the device is scheduled to be removed when it
+ * gets closed.
+ */
+#define DM_DEFERRED_REMOVE              (1 << 17) /* In/Out */
+
 #endif                          /* _LINUX_DM_IOCTL_H */