[Qemu-devel] [PATCH v6 27/42] commit: Deal with filters

[Max Reitz <mreitz@redhat.com>]

This includes some permission limiting (for example, we only need to
take the RESIZE permission if the base is smaller than the top).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/block-backend.c | 16 +++++---
 block/commit.c        | 96 +++++++++++++++++++++++++++++++------------
 blockdev.c            |  6 ++-
 3 files changed, 85 insertions(+), 33 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index c13c5c83b0..0bc592d023 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -2180,11 +2180,17 @@ int blk_commit_all(void)
         AioContext *aio_context = blk_get_aio_context(blk);
 
         aio_context_acquire(aio_context);
-        if (blk_is_inserted(blk) && blk->root->bs->backing) {
-            int ret = bdrv_commit(blk->root->bs);
-            if (ret < 0) {
-                aio_context_release(aio_context);
-                return ret;
+        if (blk_is_inserted(blk)) {
+            BlockDriverState *non_filter;
+
+            /* Legacy function, so skip implicit filters */
+            non_filter = bdrv_skip_implicit_filters(blk->root->bs);
+            if (bdrv_filtered_cow_child(non_filter)) {
+                int ret = bdrv_commit(non_filter);
+                if (ret < 0) {
+                    aio_context_release(aio_context);
+                    return ret;
+                }
             }
         }
         aio_context_release(aio_context);
diff --git a/block/commit.c b/block/commit.c
index 5a7672c7c7..40d1c8eeac 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -37,6 +37,7 @@ typedef struct CommitBlockJob {
     BlockBackend *top;
     BlockBackend *base;
     BlockDriverState *base_bs;
+    BlockDriverState *above_base;
     BlockdevOnError on_error;
     bool base_read_only;
     bool chain_frozen;
@@ -110,7 +111,7 @@ static void commit_abort(Job *job)
      * XXX Can (or should) we somehow keep 'consistent read' blocked even
      * after the failed/cancelled commit job is gone? If we already wrote
      * something to base, the intermediate images aren't valid any more. */
-    bdrv_replace_node(s->commit_top_bs, backing_bs(s->commit_top_bs),
+    bdrv_replace_node(s->commit_top_bs, s->commit_top_bs->backing->bs,
                       &error_abort);
 
     bdrv_unref(s->commit_top_bs);
@@ -174,7 +175,7 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
             break;
         }
         /* Copy if allocated above the base */
-        ret = bdrv_is_allocated_above(blk_bs(s->top), blk_bs(s->base), false,
+        ret = bdrv_is_allocated_above(blk_bs(s->top), s->above_base, true,
                                       offset, COMMIT_BUFFER_SIZE, &n);
         copy = (ret == 1);
         trace_commit_one_iteration(s, offset, n, ret);
@@ -267,15 +268,35 @@ void commit_start(const char *job_id, BlockDriverState *bs,
     CommitBlockJob *s;
     BlockDriverState *iter;
     BlockDriverState *commit_top_bs = NULL;
+    BlockDriverState *filtered_base;
     Error *local_err = NULL;
+    int64_t base_size, top_size;
+    uint64_t perms, iter_shared_perms;
     int ret;
 
     assert(top != bs);
-    if (top == base) {
+    if (bdrv_skip_rw_filters(top) == bdrv_skip_rw_filters(base)) {
         error_setg(errp, "Invalid files for merge: top and base are the same");
         return;
     }
 
+    base_size = bdrv_getlength(base);
+    if (base_size < 0) {
+        error_setg_errno(errp, -base_size, "Could not inquire base image size");
+        return;
+    }
+
+    top_size = bdrv_getlength(top);
+    if (top_size < 0) {
+        error_setg_errno(errp, -top_size, "Could not inquire top image size");
+        return;
+    }
+
+    perms = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE;
+    if (base_size < top_size) {
+        perms |= BLK_PERM_RESIZE;
+    }
+
     s = block_job_create(job_id, &commit_job_driver, NULL, bs, 0, BLK_PERM_ALL,
                          speed, creation_flags, NULL, NULL, errp);
     if (!s) {
@@ -315,17 +336,43 @@ void commit_start(const char *job_id, BlockDriverState *bs,
 
     s->commit_top_bs = commit_top_bs;
 
-    /* Block all nodes between top and base, because they will
-     * disappear from the chain after this operation. */
-    assert(bdrv_chain_contains(top, base));
-    for (iter = top; iter != base; iter = backing_bs(iter)) {
-        /* XXX BLK_PERM_WRITE needs to be allowed so we don't block ourselves
-         * at s->base (if writes are blocked for a node, they are also blocked
-         * for its backing file). The other options would be a second filter
-         * driver above s->base. */
+    /*
+     * Block all nodes between top and base, because they will
+     * disappear from the chain after this operation.
+     * Note that this assumes that the user is fine with removing all
+     * nodes (including R/W filters) between top and base.  Assuring
+     * this is the responsibility of the interface (i.e. whoever calls
+     * commit_start()).
+     */
+    s->above_base = bdrv_find_overlay(top, base);
+    assert(s->above_base);
+
+    /*
+     * The topmost node with
+     * bdrv_skip_rw_filters(filtered_base) == bdrv_skip_rw_filters(base)
+     */
+    filtered_base = bdrv_filtered_cow_bs(s->above_base);
+    assert(bdrv_skip_rw_filters(filtered_base) == bdrv_skip_rw_filters(base));
+
+    /*
+     * XXX BLK_PERM_WRITE needs to be allowed so we don't block ourselves
+     * at s->base (if writes are blocked for a node, they are also blocked
+     * for its backing file). The other options would be a second filter
+     * driver above s->base.
+     */
+    iter_shared_perms = BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE;
+
+    for (iter = top; iter != base; iter = bdrv_filtered_bs(iter)) {
+        if (iter == filtered_base) {
+            /*
+             * From here on, all nodes are filters on the base.  This
+             * allows us to share BLK_PERM_CONSISTENT_READ.
+             */
+            iter_shared_perms |= BLK_PERM_CONSISTENT_READ;
+        }
+
         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
-                                 BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE,
-                                 errp);
+                                 iter_shared_perms, errp);
         if (ret < 0) {
             goto fail;
         }
@@ -342,9 +389,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
     }
 
     s->base = blk_new(s->common.job.aio_context,
-                      BLK_PERM_CONSISTENT_READ
-                      | BLK_PERM_WRITE
-                      | BLK_PERM_RESIZE,
+                      perms,
                       BLK_PERM_CONSISTENT_READ
                       | BLK_PERM_GRAPH_MOD
                       | BLK_PERM_WRITE_UNCHANGED);
@@ -412,19 +457,22 @@ int bdrv_commit(BlockDriverState *bs)
     if (!drv)
         return -ENOMEDIUM;
 
-    if (!bs->backing) {
+    backing_file_bs = bdrv_filtered_cow_bs(bs);
+
+    if (!backing_file_bs) {
         return -ENOTSUP;
     }
 
     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT_SOURCE, NULL) ||
-        bdrv_op_is_blocked(bs->backing->bs, BLOCK_OP_TYPE_COMMIT_TARGET, NULL)) {
+        bdrv_op_is_blocked(backing_file_bs, BLOCK_OP_TYPE_COMMIT_TARGET, NULL))
+    {
         return -EBUSY;
     }
 
-    ro = bs->backing->bs->read_only;
+    ro = backing_file_bs->read_only;
 
     if (ro) {
-        if (bdrv_reopen_set_read_only(bs->backing->bs, false, NULL)) {
+        if (bdrv_reopen_set_read_only(backing_file_bs, false, NULL)) {
             return -EACCES;
         }
     }
@@ -440,8 +488,6 @@ int bdrv_commit(BlockDriverState *bs)
     }
 
     /* Insert commit_top block node above backing, so we can write to it */
-    backing_file_bs = backing_bs(bs);
-
     commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, NULL, BDRV_O_RDWR,
                                          &local_err);
     if (commit_top_bs == NULL) {
@@ -526,15 +572,13 @@ ro_cleanup:
     qemu_vfree(buf);
 
     blk_unref(backing);
-    if (backing_file_bs) {
-        bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
-    }
+    bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
     bdrv_unref(commit_top_bs);
     blk_unref(src);
 
     if (ro) {
         /* ignoring error return here */
-        bdrv_reopen_set_read_only(bs->backing->bs, true, NULL);
+        bdrv_reopen_set_read_only(backing_file_bs, true, NULL);
     }
 
     return ret;
diff --git a/blockdev.c b/blockdev.c
index c6f79b4e0e..7bef41c0b0 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1094,7 +1094,7 @@ void hmp_commit(Monitor *mon, const QDict *qdict)
             return;
         }
 
-        bs = blk_bs(blk);
+        bs = bdrv_skip_implicit_filters(blk_bs(blk));
         aio_context = bdrv_get_aio_context(bs);
         aio_context_acquire(aio_context);
 
@@ -3454,7 +3454,9 @@ void qmp_block_commit(bool has_job_id, const char *job_id, const char *device,
 
     assert(bdrv_get_aio_context(base_bs) == aio_context);
 
-    for (iter = top_bs; iter != backing_bs(base_bs); iter = backing_bs(iter)) {
+    for (iter = top_bs; iter != bdrv_filtered_bs(base_bs);
+         iter = bdrv_filtered_bs(iter))
+    {
         if (bdrv_op_is_blocked(iter, BLOCK_OP_TYPE_COMMIT_TARGET, errp)) {
             goto out;
         }
-- 
2.21.0