[Qemu-block] [PATCH 07/18] block/mirror: Wait for in-flight op conflicts

[Max Reitz]

This patch makes the mirror code differentiate between simply waiting
for any operation to complete (mirror_wait_for_free_in_flight_slot())
and specifically waiting for all operations touching a certain range of
the virtual disk to complete (mirror_wait_on_conflicts()).

Signed-off-by: Max Reitz <address@hidden>
---
 block/mirror.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 70 insertions(+), 15 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 81253fbad1..2ece38094d 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -14,6 +14,7 @@
 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "qemu/coroutine.h"
+#include "qemu/range.h"
 #include "trace.h"
 #include "block/blockjob_int.h"
 #include "block/block_int.h"
@@ -111,6 +112,41 @@ static BlockErrorAction mirror_error_action(MirrorBlockJob 
*s, bool read,
     }
 }
 
+static void coroutine_fn mirror_wait_on_conflicts(MirrorOp *self,
+                                                  MirrorBlockJob *s,
+                                                  uint64_t offset,
+                                                  uint64_t bytes)
+{
+    uint64_t self_start_chunk = offset / s->granularity;
+    uint64_t self_end_chunk = DIV_ROUND_UP(offset + bytes, s->granularity);
+    uint64_t self_nb_chunks = self_end_chunk - self_start_chunk;
+
+    while (find_next_bit(s->in_flight_bitmap, self_end_chunk,
+                         self_start_chunk) < self_end_chunk &&
+           s->ret >= 0)
+    {
+        MirrorOp *op;
+
+        QTAILQ_FOREACH(op, &s->ops_in_flight, next) {
+            uint64_t op_start_chunk = op->offset / s->granularity;
+            uint64_t op_nb_chunks = DIV_ROUND_UP(op->offset + op->bytes,
+                                                 s->granularity) -
+                                    op_start_chunk;
+
+            if (op == self) {
+                continue;
+            }
+
+            if (ranges_overlap(self_start_chunk, self_nb_chunks,
+                               op_start_chunk, op_nb_chunks))
+            {
+                qemu_co_queue_wait(&op->waiting_requests, NULL);
+                break;
+            }
+        }
+    }
+}
+
 static void coroutine_fn mirror_iteration_done(MirrorOp *op, int ret)
 {
     MirrorBlockJob *s = op->s;
@@ -238,7 +274,7 @@ static int mirror_cow_align(MirrorBlockJob *s, int64_t 
*offset,
     return ret;
 }
 
-static inline void mirror_wait_for_io(MirrorBlockJob *s)
+static inline void mirror_wait_for_free_in_flight_slot(MirrorBlockJob *s)
 {
     MirrorOp *op;
 
@@ -287,7 +323,7 @@ static void coroutine_fn mirror_co_read(void *opaque)
 
     while (s->buf_free_count < nb_chunks) {
         trace_mirror_yield_in_flight(s, op->offset, s->in_flight);
-        mirror_wait_for_io(s);
+        mirror_wait_for_free_in_flight_slot(s);
     }
 
     /* Now make a QEMUIOVector taking enough granularity-sized chunks
@@ -381,8 +417,9 @@ static unsigned mirror_perform(MirrorBlockJob *s, int64_t 
offset,
 static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
 {
     BlockDriverState *source = s->source;
-    int64_t offset, first_chunk;
-    uint64_t delay_ns = 0;
+    MirrorOp *pseudo_op;
+    int64_t offset;
+    uint64_t delay_ns = 0, ret = 0;
     /* At least the first dirty chunk is mirrored in one iteration. */
     int nb_chunks = 1;
     int sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
@@ -400,11 +437,7 @@ static uint64_t coroutine_fn 
mirror_iteration(MirrorBlockJob *s)
     }
     bdrv_dirty_bitmap_unlock(s->dirty_bitmap);
 
-    first_chunk = offset / s->granularity;
-    while (test_bit(first_chunk, s->in_flight_bitmap)) {
-        trace_mirror_yield_in_flight(s, offset, s->in_flight);
-        mirror_wait_for_io(s);
-    }
+    mirror_wait_on_conflicts(NULL, s, offset, 1);
 
     block_job_pause_point(&s->common);
 
@@ -442,6 +475,20 @@ static uint64_t coroutine_fn 
mirror_iteration(MirrorBlockJob *s)
                                    nb_chunks * sectors_per_chunk);
     bdrv_dirty_bitmap_unlock(s->dirty_bitmap);
 
+    /* Before claiming an area in the in-flight bitmap, we have to
+     * create a MirrorOp for it so that conflicting requests can wait
+     * for it.  mirror_perform() will create the real MirrorOps later,
+     * for now we just create a pseudo operation that will wake up all
+     * conflicting requests once all real operations have been
+     * launched. */
+    pseudo_op = g_new(MirrorOp, 1);
+    *pseudo_op = (MirrorOp){
+        .offset = offset,
+        .bytes  = nb_chunks * s->granularity,
+    };
+    qemu_co_queue_init(&pseudo_op->waiting_requests);
+    QTAILQ_INSERT_TAIL(&s->ops_in_flight, pseudo_op, next);
+
     bitmap_set(s->in_flight_bitmap, offset / s->granularity, nb_chunks);
     while (nb_chunks > 0 && offset < s->bdev_length) {
         int64_t ret;
@@ -481,11 +528,12 @@ static uint64_t coroutine_fn 
mirror_iteration(MirrorBlockJob *s)
 
         while (s->in_flight >= MAX_IN_FLIGHT) {
             trace_mirror_yield_in_flight(s, offset, s->in_flight);
-            mirror_wait_for_io(s);
+            mirror_wait_for_free_in_flight_slot(s);
         }
 
         if (s->ret < 0) {
-            return 0;
+            ret = 0;
+            goto fail;
         }
 
         io_bytes = mirror_clip_bytes(s, offset, io_bytes);
@@ -502,7 +550,14 @@ static uint64_t coroutine_fn 
mirror_iteration(MirrorBlockJob *s)
             delay_ns = ratelimit_calculate_delay(&s->limit, io_bytes_acct);
         }
     }
-    return delay_ns;
+
+    ret = delay_ns;
+fail:
+    QTAILQ_REMOVE(&s->ops_in_flight, pseudo_op, next);
+    qemu_co_queue_restart_all(&pseudo_op->waiting_requests);
+    g_free(pseudo_op);
+
+    return ret;
 }
 
 static void mirror_free_init(MirrorBlockJob *s)
@@ -529,7 +584,7 @@ static void mirror_free_init(MirrorBlockJob *s)
 static void mirror_wait_for_all_io(MirrorBlockJob *s)
 {
     while (s->in_flight > 0) {
-        mirror_wait_for_io(s);
+        mirror_wait_for_free_in_flight_slot(s);
     }
 }
 
@@ -685,7 +740,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
             if (s->in_flight >= MAX_IN_FLIGHT) {
                 trace_mirror_yield(s, UINT64_MAX, s->buf_free_count,
                                    s->in_flight);
-                mirror_wait_for_io(s);
+                mirror_wait_for_free_in_flight_slot(s);
                 continue;
             }
 
@@ -868,7 +923,7 @@ static void coroutine_fn mirror_run(void *opaque)
                 (cnt == 0 && s->in_flight > 0)) {
                 trace_mirror_yield(s, cnt * BDRV_SECTOR_SIZE,
                                    s->buf_free_count, s->in_flight);
-                mirror_wait_for_io(s);
+                mirror_wait_for_free_in_flight_slot(s);
                 continue;
             } else if (cnt != 0) {
                 delay_ns = mirror_iteration(s);
-- 
2.13.5