dm ioctl: return UUID in DM_LIST_DEVICES_CMD result

When LVM needs to find a device with a particular UUID it needs to ask for
UUID for each device. This patch returns UUID directly in the list of
devices, so that LVM doesn't have to query all the devices with an ioctl.
The UUID is returned if the flag DM_UUID_FLAG is set in the parameters.

Returning UUID is done in backward-compatible way. There's one unused
32-bit word value after the event number. This patch sets the bit
DM_NAME_LIST_FLAG_HAS_UUID if UUID is present and
DM_NAME_LIST_FLAG_DOESNT_HAVE_UUID if it isn't (if none of these bits is
set, then we have an old kernel that doesn't support returning UUIDs). The
UUID is stored after this word. The 'next' value is updated to point after
the UUID, so that old version of libdevmapper will skip the UUID without
attempting to interpret it.

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

1 files changed, 17 insertions, 3 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 272de8772d52..0812ac6e9d70 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -558,7 +558,9 @@ static int list_devices(struct file *filp, struct dm_ioctl *param, size_t param_
 	for (n = rb_first(&name_rb_tree); n; n = rb_next(n)) {
 		hc = container_of(n, struct hash_cell, name_node);
 		needed += align_val(offsetof(struct dm_name_list, name) + strlen(hc->name) + 1);
-		needed += align_val(sizeof(uint32_t));
+		needed += align_val(sizeof(uint32_t) * 2);
+		if (param->flags & DM_UUID_FLAG && hc->uuid)
+			needed += align_val(strlen(hc->uuid) + 1);
 	}
 
 	/*
@@ -577,6 +579,7 @@ static int list_devices(struct file *filp, struct dm_ioctl *param, size_t param_
 	 * Now loop through filling out the names.
 	 */
 	for (n = rb_first(&name_rb_tree); n; n = rb_next(n)) {
+		void *uuid_ptr;
 		hc = container_of(n, struct hash_cell, name_node);
 		if (old_nl)
 			old_nl->next = (uint32_t) ((void *) nl -
@@ -588,8 +591,19 @@ static int list_devices(struct file *filp, struct dm_ioctl *param, size_t param_
 
 		old_nl = nl;
 		event_nr = align_ptr(nl->name + strlen(hc->name) + 1);
-		*event_nr = dm_get_event_nr(hc->md);
-		nl = align_ptr(event_nr + 1);
+		event_nr[0] = dm_get_event_nr(hc->md);
+		event_nr[1] = 0;
+		uuid_ptr = align_ptr(event_nr + 2);
+		if (param->flags & DM_UUID_FLAG) {
+			if (hc->uuid) {
+				event_nr[1] |= DM_NAME_LIST_FLAG_HAS_UUID;
+				strcpy(uuid_ptr, hc->uuid);
+				uuid_ptr = align_ptr(uuid_ptr + strlen(hc->uuid) + 1);
+			} else {
+				event_nr[1] |= DM_NAME_LIST_FLAG_DOESNT_HAVE_UUID;
+			}
+		}
+		nl = uuid_ptr;
 	}
 	/*
 	 * If mismatch happens, security may be compromised due to buffer