rbd: define image request originator flag

Define a flag indicating whether an image request originated from
the Linux block layer (from blk_fetch_request()) or whether it was
initiated in order to satisfy an object request for a child image
of a layered rbd device.  For image requests initiated by objects of
child images we'll save a pointer to the object request rather than
the Linux block request.

For now, only block requests are used.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 5ea2e36..7ecd909 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -203,18 +203,22 @@ struct rbd_obj_request {
 };
 
 enum img_req_flags {
-       IMG_REQ_WRITE,          /* read = 0, write = 1 */
+       IMG_REQ_WRITE,          /* I/O direction: read = 0, write = 1 */
+       IMG_REQ_CHILD,          /* initiator: block = 0, child image = 1 */
 };
 
 struct rbd_img_request {
-       struct request          *rq;
        struct rbd_device       *rbd_dev;
        u64                     offset; /* starting image byte offset */
        u64                     length; /* byte count from offset */
        unsigned long           flags;
        union {
+               u64                     snap_id;        /* for reads */
                struct ceph_snap_context *snapc;        /* for writes */
-               u64             snap_id;                /* for reads */
+       };
+       union {
+               struct request          *rq;            /* block request */
+               struct rbd_obj_request  *obj_request;   /* obj req initiator */
        };
        spinlock_t              completion_lock;/* protects next_completion */
        u32                     next_completion;
@@ -1231,6 +1235,18 @@ static bool img_request_write_test(struct rbd_img_request *img_request)
        return test_bit(IMG_REQ_WRITE, &img_request->flags) != 0;
 }
 
+static void img_request_child_set(struct rbd_img_request *img_request)
+{
+       set_bit(IMG_REQ_CHILD, &img_request->flags);
+       smp_mb();
+}
+
+static bool img_request_child_test(struct rbd_img_request *img_request)
+{
+       smp_mb();
+       return test_bit(IMG_REQ_CHILD, &img_request->flags) != 0;
+}
+
 static void
 rbd_img_obj_request_read_callback(struct rbd_obj_request *obj_request)
 {
@@ -1499,7 +1515,8 @@ static void rbd_obj_request_destroy(struct kref *kref)
 static struct rbd_img_request *rbd_img_request_create(
                                        struct rbd_device *rbd_dev,
                                        u64 offset, u64 length,
-                                       bool write_request)
+                                       bool write_request,
+                                       bool child_request)
 {
        struct rbd_img_request *img_request;
        struct ceph_snap_context *snapc = NULL;
@@ -1530,6 +1547,8 @@ static struct rbd_img_request *rbd_img_request_create(
        } else {
                img_request->snap_id = rbd_dev->spec->snap_id;
        }
+       if (child_request)
+               img_request_child_set(img_request);
        spin_lock_init(&img_request->completion_lock);
        img_request->next_completion = 0;
        img_request->callback = NULL;
@@ -1578,7 +1597,9 @@ static void rbd_img_obj_callback(struct rbd_obj_request *obj_request)
 
        dout("%s: img %p obj %p\n", __func__, img_request, obj_request);
        rbd_assert(img_request != NULL);
+       rbd_assert(!img_request_child_test(img_request))
        rbd_assert(img_request->rq != NULL);
+
        rbd_assert(img_request->obj_request_count > 0);
        rbd_assert(which != BAD_WHICH);
        rbd_assert(which < img_request->obj_request_count);
@@ -2012,7 +2033,7 @@ static void rbd_request_fn(struct request_queue *q)
 
                result = -ENOMEM;
                img_request = rbd_img_request_create(rbd_dev, offset, length,
-                                                       write_request);
+                                                       write_request, false);
                if (!img_request)
                        goto end_request;