block: apply COR-filter to block-stream jobs

This patch completes the series with the COR-filter applied to
block-stream operations.

Adding the filter makes it possible in future implement discarding
copied regions in backing files during the block-stream job, to reduce
the disk overuse (we need control on permissions).

Also, the filter now is smart enough to do copy-on-read with specified
base, so we have benefit on guest reads even when doing block-stream of
the part of the backing chain.

Several iotests are slightly modified due to filter insertion.

Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201216061703.70908-14-vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/stream.c

@@ -17,8 +17,10 @@
 #include "block/blockjob_int.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qdict.h"
 #include "qemu/ratelimit.h"
 #include "sysemu/block-backend.h"
+#include "block/copy-on-read.h"
 
 enum {
     /*
@@ -33,11 +35,11 @@ typedef struct StreamBlockJob {
     BlockJob common;
     BlockDriverState *base_overlay; /* COW overlay (stream from this) */
     BlockDriverState *above_base;   /* Node directly above the base */
+    BlockDriverState *cor_filter_bs;
     BlockDriverState *target_bs;
     BlockdevOnError on_error;
     char *backing_file_str;
     bool bs_read_only;
-    bool chain_frozen;
 } StreamBlockJob;
 
 static int coroutine_fn stream_populate(BlockBackend *blk,
@@ -45,17 +47,7 @@ static int coroutine_fn stream_populate(BlockBackend *blk,
 {
     assert(bytes < SIZE_MAX);
 
-    return blk_co_preadv(blk, offset, bytes, NULL,
-                         BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH);
-}
-
-static void stream_abort(Job *job)
-{
-    StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
-
-    if (s->chain_frozen) {
-        bdrv_unfreeze_backing_chain(s->target_bs, s->above_base);
-    }
+    return blk_co_preadv(blk, offset, bytes, NULL, BDRV_REQ_PREFETCH);
 }
 
 static int stream_prepare(Job *job)
@@ -67,8 +59,9 @@ static int stream_prepare(Job *job)
     Error *local_err = NULL;
     int ret = 0;
 
-    bdrv_unfreeze_backing_chain(s->target_bs, s->above_base);
-    s->chain_frozen = false;
+    /* We should drop filter at this point, as filter hold the backing chain */
+    bdrv_cor_filter_drop(s->cor_filter_bs);
+    s->cor_filter_bs = NULL;
 
     if (bdrv_cow_child(unfiltered_bs)) {
         const char *base_id = NULL, *base_fmt = NULL;
@@ -94,6 +87,11 @@ static void stream_clean(Job *job)
     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
     BlockJob *bjob = &s->common;
 
+    if (s->cor_filter_bs) {
+        bdrv_cor_filter_drop(s->cor_filter_bs);
+        s->cor_filter_bs = NULL;
+    }
+
     /* Reopen the image back in read-only mode if necessary */
     if (s->bs_read_only) {
         /* Give up write permissions before making it read-only */
@@ -109,7 +107,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp)
     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
     BlockBackend *blk = s->common.blk;
     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
-    bool enable_cor = !bdrv_cow_child(s->base_overlay);
     int64_t len;
     int64_t offset = 0;
     uint64_t delay_ns = 0;
@@ -127,15 +124,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp)
     }
     job_progress_set_remaining(&s->common.job, len);
 
-    /* Turn on copy-on-read for the whole block device so that guest read
-     * requests help us make progress.  Only do this when copying the entire
-     * backing chain since the copy-on-read operation does not take base into
-     * account.
-     */
-    if (enable_cor) {
-        bdrv_enable_copy_on_read(s->target_bs);
-    }
-
     for ( ; offset < len; offset += n) {
         bool copy;
         int ret;
@@ -194,10 +182,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp)
         }
     }
 
-    if (enable_cor) {
-        bdrv_disable_copy_on_read(s->target_bs);
-    }
-
     /* Do not remove the backing file if an error was there but ignored. */
     return error;
 }
@@ -209,7 +193,6 @@ static const BlockJobDriver stream_job_driver = {
         .free          = block_job_free,
         .run           = stream_run,
         .prepare       = stream_prepare,
-        .abort         = stream_abort,
         .clean         = stream_clean,
         .user_resume   = block_job_user_resume,
     },
@@ -228,7 +211,9 @@ void stream_start(const char *job_id, BlockDriverState *bs,
     bool bs_read_only;
     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
     BlockDriverState *base_overlay;
+    BlockDriverState *cor_filter_bs = NULL;
     BlockDriverState *above_base;
+    QDict *opts;
 
     assert(!(base && bottom));
     assert(!(backing_file_str && bottom));
@@ -266,30 +251,62 @@ void stream_start(const char *job_id, BlockDriverState *bs,
         }
     }
 
-    if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
-        return;
-    }
-
     /* Make sure that the image is opened in read-write mode */
     bs_read_only = bdrv_is_read_only(bs);
     if (bs_read_only) {
-        if (bdrv_reopen_set_read_only(bs, false, errp) != 0) {
-            bs_read_only = false;
-            goto fail;
+        int ret;
+        /* Hold the chain during reopen */
+        if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
+            return;
+        }
+
+        ret = bdrv_reopen_set_read_only(bs, false, errp);
+
+        /* failure, or cor-filter will hold the chain */
+        bdrv_unfreeze_backing_chain(bs, above_base);
+
+        if (ret < 0) {
+            return;
         }
     }
 
-    /* Prevent concurrent jobs trying to modify the graph structure here, we
-     * already have our own plans. Also don't allow resize as the image size is
-     * queried only at the job start and then cached. */
-    s = block_job_create(job_id, &stream_job_driver, NULL, bs,
-                         basic_flags | BLK_PERM_GRAPH_MOD,
+    opts = qdict_new();
+
+    qdict_put_str(opts, "driver", "copy-on-read");
+    qdict_put_str(opts, "file", bdrv_get_node_name(bs));
+    /* Pass the base_overlay node name as 'bottom' to COR driver */
+    qdict_put_str(opts, "bottom", base_overlay->node_name);
+    if (filter_node_name) {
+        qdict_put_str(opts, "node-name", filter_node_name);
+    }
+
+    cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
+    if (!cor_filter_bs) {
+        goto fail;
+    }
+
+    if (!filter_node_name) {
+        cor_filter_bs->implicit = true;
+    }
+
+    s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
+                         BLK_PERM_CONSISTENT_READ,
                          basic_flags | BLK_PERM_WRITE,
                          speed, creation_flags, NULL, NULL, errp);
     if (!s) {
         goto fail;
     }
 
+    /*
+     * Prevent concurrent jobs trying to modify the graph structure here, we
+     * already have our own plans. Also don't allow resize as the image size is
+     * queried only at the job start and then cached.
+     */
+    if (block_job_add_bdrv(&s->common, "active node", bs, 0,
+                           basic_flags | BLK_PERM_WRITE, &error_abort)) {
+        goto fail;
+    }
+
     /* Block all intermediate nodes between bs and base, because they will
      * disappear from the chain after this operation. The streaming job reads
      * every block only once, assuming that it doesn't change, so forbid writes
@@ -310,9 +327,9 @@ void stream_start(const char *job_id, BlockDriverState *bs,
     s->base_overlay = base_overlay;
     s->above_base = above_base;
     s->backing_file_str = g_strdup(backing_file_str);
+    s->cor_filter_bs = cor_filter_bs;
     s->target_bs = bs;
     s->bs_read_only = bs_read_only;
-    s->chain_frozen = true;
 
     s->on_error = on_error;
     trace_stream_start(bs, base, s);
@@ -320,8 +337,10 @@ void stream_start(const char *job_id, BlockDriverState *bs,
     return;
 
 fail:
+    if (cor_filter_bs) {
+        bdrv_cor_filter_drop(cor_filter_bs);
+    }
     if (bs_read_only) {
         bdrv_reopen_set_read_only(bs, true, NULL);
     }
-    bdrv_unfreeze_backing_chain(bs, above_base);
 }

tests/qemu-iotests/030

@@ -279,12 +279,14 @@ class TestParallelOps(iotests.QMPTestCase):
         self.assert_no_active_block_jobs()
 
         # Set a speed limit to make sure that this job blocks the rest
-        result = self.vm.qmp('block-stream', device='node4', job_id='stream-node4', base=self.imgs[1], speed=1024*1024)
+        result = self.vm.qmp('block-stream', device='node4',
+                             job_id='stream-node4', base=self.imgs[1],
+                             filter_node_name='stream-filter', speed=1024*1024)
         self.assert_qmp(result, 'return', {})
 
         result = self.vm.qmp('block-stream', device='node5', job_id='stream-node5', base=self.imgs[2])
         self.assert_qmp(result, 'error/desc',
-            "Node 'node4' is busy: block device is in use by block job: stream")
+            "Node 'stream-filter' is busy: block device is in use by block job: stream")
 
         result = self.vm.qmp('block-stream', device='node3', job_id='stream-node3', base=self.imgs[2])
         self.assert_qmp(result, 'error/desc',
@@ -297,7 +299,7 @@ class TestParallelOps(iotests.QMPTestCase):
         # block-commit should also fail if it touches nodes used by the stream job
         result = self.vm.qmp('block-commit', device='drive0', base=self.imgs[4], job_id='commit-node4')
         self.assert_qmp(result, 'error/desc',
-            "Node 'node4' is busy: block device is in use by block job: stream")
+            "Node 'stream-filter' is busy: block device is in use by block job: stream")
 
         result = self.vm.qmp('block-commit', device='drive0', base=self.imgs[1], top=self.imgs[3], job_id='commit-node1')
         self.assert_qmp(result, 'error/desc',

tests/qemu-iotests/141.out

@@ -165,7 +165,7 @@ wrote 1048576/1048576 bytes at offset 0
 {"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "job0"}}
 {'execute': 'blockdev-del',
           'arguments': {'node-name': 'drv0'}}
-{"error": {"class": "GenericError", "desc": "Node drv0 is in use"}}
+{"error": {"class": "GenericError", "desc": "Node 'drv0' is busy: block device is in use by block job: stream"}}
 {'execute': 'block-job-cancel',
           'arguments': {'device': 'job0'}}
 {"return": {}}

tests/qemu-iotests/245

@@ -893,20 +893,24 @@ class TestBlockdevReopen(iotests.QMPTestCase):
 
         # hd1 <- hd0
         result = self.vm.qmp('block-stream', conv_keys = True, job_id = 'stream0',
-                             device = 'hd1', auto_finalize = False)
+                             device = 'hd1', filter_node_name='cor',
+                             auto_finalize = False)
         self.assert_qmp(result, 'return', {})
 
-        # We can't reopen with the original options because that would
-        # make hd1 read-only and block-stream requires it to be read-write
-        # (Which error message appears depends on whether the stream job is
-        # already done with copying at this point.)
+        # We can't reopen with the original options because there is a filter
+        # inserted by stream job above hd1.
         self.reopen(opts, {},
-            ["Can't set node 'hd1' to r/o with copy-on-read enabled",
-             "Cannot make block node read-only, there is a writer on it"])
+                    "Cannot change the option 'backing.backing.file.node-name'")
+
+        # We can't reopen hd1 to read-only, as block-stream requires it to be
+        # read-write
+        self.reopen(opts['backing'], {'read-only': True},
+                    "Cannot make block node read-only, there is a writer on it")
 
         # We can't remove hd2 while the stream job is ongoing
         opts['backing']['backing'] = None
-        self.reopen(opts, {'backing.read-only': False}, "Cannot change 'backing' link from 'hd1' to 'hd2'")
+        self.reopen(opts['backing'], {'read-only': False},
+                    "Cannot change 'backing' link from 'hd1' to 'hd2'")
 
         # We can detach hd1 from hd0 because it doesn't affect the stream job
         opts['backing'] = None