block: Let format drivers pass @exact

When truncating a format node, the @exact parameter is generally handled
simply by virtue of the format storing the new size in the image
metadata.  Such formats do not need to pass on the parameter to their
file nodes.

There are exceptions, though:
- raw and crypto cannot store the image size, and thus must pass on
  @exact.

- When using qcow2 with an external data file, it just makes sense to
  keep its size in sync with the qcow2 virtual disk (because the
  external data file is the virtual disk).  Therefore, we should pass
  @exact when truncating it.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190918095144.955-7-mreitz@redhat.com
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

diff --git a/block/crypto.c b/block/crypto.c
index e5a1a2cdf301b060c4cf546759dcf7fe362696cd..24823835c1c228d8b1f0456681c80551587ba9b3 100644 (file)
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -311,7 +311,7 @@ block_crypto_co_truncate(BlockDriverState *bs, int64_t offset, bool exact,
 
     offset += payload_offset;
 
-    return bdrv_co_truncate(bs->file, offset, false, prealloc, errp);
+    return bdrv_co_truncate(bs->file, offset, exact, prealloc, errp);
 }
 
 static void block_crypto_close(BlockDriverState *bs)

diff --git a/block/qcow2.c b/block/qcow2.c
index de284ad80347001cb67a48dcc6bc9661aec48300..9f32dae41f7e61cbb7b9d633d23702ff0cef3c08 100644 (file)
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4027,6 +4027,13 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
         if ((last_cluster + 1) * s->cluster_size < old_file_size) {
             Error *local_err = NULL;
 
+            /*
+             * Do not pass @exact here: It will not help the user if
+             * we get an error here just because they wanted to shrink
+             * their qcow2 image (on a block device) with qemu-img.
+             * (And on the qcow2 layer, the @exact requirement is
+             * always fulfilled, so there is no need to pass it on.)
+             */
             bdrv_co_truncate(bs->file, (last_cluster + 1) * s->cluster_size,
                              false, PREALLOC_MODE_OFF, &local_err);
             if (local_err) {
@@ -4045,7 +4052,12 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
     switch (prealloc) {
     case PREALLOC_MODE_OFF:
         if (has_data_file(bs)) {
-            ret = bdrv_co_truncate(s->data_file, offset, false, prealloc, errp);
+            /*
+             * If the caller wants an exact resize, the external data
+             * file should be resized to the exact target size, too,
+             * so we pass @exact here.
+             */
+            ret = bdrv_co_truncate(s->data_file, offset, exact, prealloc, errp);
             if (ret < 0) {
                 goto fail;
             }
@@ -4130,6 +4142,7 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
         /* Allocate the data area */
         new_file_size = allocation_start +
                         nb_new_data_clusters * s->cluster_size;
+        /* Image file grows, so @exact does not matter */
         ret = bdrv_co_truncate(bs->file, new_file_size, false, prealloc, errp);
         if (ret < 0) {
             error_prepend(errp, "Failed to resize underlying file: ");

diff --git a/block/raw-format.c b/block/raw-format.c
index 57d84d0bae6e9b43e4f43ccb8805ba9c166ba70e..3a76ec7dd21bf6e76ec5bcb962ab34daf16a4389 100644 (file)
--- a/block/raw-format.c
+++ b/block/raw-format.c
@@ -387,7 +387,7 @@ static int coroutine_fn raw_co_truncate(BlockDriverState *bs, int64_t offset,
 
     s->size = offset;
     offset += s->offset;
-    return bdrv_co_truncate(bs->file, offset, false, prealloc, errp);
+    return bdrv_co_truncate(bs->file, offset, exact, prealloc, errp);
 }
 
 static void raw_eject(BlockDriverState *bs, bool eject_flag)