1 files changed, 109 insertions, 0 deletions
diff --git a/block/io.c b/block/io.c
index ef4fedd364..7e87a42b8e 100644
--- a/block/io.c
+++ b/block/io.c
@@ -3020,3 +3020,112 @@ int coroutine_fn bdrv_co_copy_range(BdrvChild *src, uint64_t src_offset,
     bdrv_dec_in_flight(dst_bs);
     return ret;
 }
+
+static void bdrv_parent_cb_resize(BlockDriverState *bs)
+{
+    BdrvChild *c;
+    QLIST_FOREACH(c, &bs->parents, next_parent) {
+        if (c->role->resize) {
+            c->role->resize(c);
+        }
+    }
+}
+
+/**
+ * Truncate file to 'offset' bytes (needed only for file protocols)
+ */
+int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset,
+                                  PreallocMode prealloc, Error **errp)
+{
+    BlockDriverState *bs = child->bs;
+    BlockDriver *drv = bs->drv;
+    int ret;
+
+    assert(child->perm & BLK_PERM_RESIZE);
+
+    /* if bs->drv == NULL, bs is closed, so there's nothing to do here */
+    if (!drv) {
+        error_setg(errp, "No medium inserted");
+        return -ENOMEDIUM;
+    }
+    if (offset < 0) {
+        error_setg(errp, "Image size cannot be negative");
+        return -EINVAL;
+    }
+
+    bdrv_inc_in_flight(bs);
+
+    if (!drv->bdrv_co_truncate) {
+        if (bs->file && drv->is_filter) {
+            ret = bdrv_co_truncate(bs->file, offset, prealloc, errp);
+            goto out;
+        }
+        error_setg(errp, "Image format driver does not support resize");
+        ret = -ENOTSUP;
+        goto out;
+    }
+    if (bs->read_only) {
+        error_setg(errp, "Image is read-only");
+        ret = -EACCES;
+        goto out;
+    }
+
+    assert(!(bs->open_flags & BDRV_O_INACTIVE));
+
+    ret = drv->bdrv_co_truncate(bs, offset, prealloc, errp);
+    if (ret < 0) {
+        goto out;
+    }
+    ret = refresh_total_sectors(bs, offset >> BDRV_SECTOR_BITS);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Could not refresh total sector count");
+    } else {
+        offset = bs->total_sectors * BDRV_SECTOR_SIZE;
+    }
+    bdrv_dirty_bitmap_truncate(bs, offset);
+    bdrv_parent_cb_resize(bs);
+    atomic_inc(&bs->write_gen);
+
+out:
+    bdrv_dec_in_flight(bs);
+    return ret;
+}
+
+typedef struct TruncateCo {
+    BdrvChild *child;
+    int64_t offset;
+    PreallocMode prealloc;
+    Error **errp;
+    int ret;
+} TruncateCo;
+
+static void coroutine_fn bdrv_truncate_co_entry(void *opaque)
+{
+    TruncateCo *tco = opaque;
+    tco->ret = bdrv_co_truncate(tco->child, tco->offset, tco->prealloc,
+                                tco->errp);
+}
+
+int bdrv_truncate(BdrvChild *child, int64_t offset, PreallocMode prealloc,
+                  Error **errp)
+{
+    Coroutine *co;
+    TruncateCo tco = {
+        .child      = child,
+        .offset     = offset,
+        .prealloc   = prealloc,
+        .errp       = errp,
+        .ret        = NOT_DONE,
+    };
+
+    if (qemu_in_coroutine()) {
+        /* Fast-path if already in coroutine context */
+        bdrv_truncate_co_entry(&tco);
+    } else {
+        co = qemu_coroutine_create(bdrv_truncate_co_entry, &tco);
+        qemu_coroutine_enter(co);
+        BDRV_POLL_WHILE(child->bs, tco.ret == NOT_DONE);
+    }
+
+    return tco.ret;
+}