[qemu-xen staging] block: nbd: Fix convert qcow2 compressed to nbd

[patchbot@xxxxxxx]

commit a2b333c01880f56056d50c238834d62e32001e54
Author:     Nir Soffer <nirsof@xxxxxxxxx>
AuthorDate: Tue Jul 28 00:58:43 2020 +0300
Commit:     Eric Blake <eblake@xxxxxxxxxx>
CommitDate: Tue Jul 28 09:54:19 2020 -0500

    block: nbd: Fix convert qcow2 compressed to nbd
    
    When converting to qcow2 compressed format, the last step is a special
    zero length compressed write, ending in a call to bdrv_co_truncate(). This
    call always fails for the nbd driver since it does not implement
    bdrv_co_truncate().
    
    For block devices, which have the same limits, the call succeeds since
    the file driver implements bdrv_co_truncate(). If the caller asked to
    truncate to the same or smaller size with exact=false, the truncate
    succeeds. Implement the same logic for nbd.
    
    Example failing without this change:
    
    In one shell start qemu-nbd:
    
    $ truncate -s 1g test.tar
    $ qemu-nbd --socket=/tmp/nbd.sock --persistent --format=raw --offset 1536 
test.tar
    
    In another shell convert an image to qcow2 compressed via NBD:
    
    $ echo "disk data" > disk.raw
    $ truncate -s 1g disk.raw
    $ qemu-img convert -f raw -O qcow2 -c disk1.raw 
nbd+unix:///?socket=/tmp/nbd.sock; echo $?
    1
    
    qemu-img failed, but the conversion was successful:
    
    $ qemu-img info nbd+unix:///?socket=/tmp/nbd.sock
    image: nbd+unix://?socket=/tmp/nbd.sock
    file format: qcow2
    virtual size: 1 GiB (1073741824 bytes)
    ...
    
    $ qemu-img check nbd+unix:///?socket=/tmp/nbd.sock
    No errors were found on the image.
    1/16384 = 0.01% allocated, 100.00% fragmented, 100.00% compressed clusters
    Image end offset: 393216
    
    $ qemu-img compare disk.raw nbd+unix:///?socket=/tmp/nbd.sock
    Images are identical.
    
    Fixes: https://bugzilla.redhat.com/1860627
    Signed-off-by: Nir Soffer <nsoffer@xxxxxxxxxx>
    Message-Id: <20200727215846.395443-2-nsoffer@xxxxxxxxxx>
    Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
    Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
    [eblake: typo fixes]
    Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
---
 block/nbd.c    | 30 ++++++++++++++++++++++++++++++
 qemu-io-cmds.c |  2 +-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/block/nbd.c b/block/nbd.c
index 65a4f56924..8934bcb479 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -1966,6 +1966,33 @@ static void nbd_close(BlockDriverState *bs)
     nbd_clear_bdrvstate(s);
 }
 
+/*
+ * NBD cannot truncate, but if the caller asks to truncate to the same size, or
+ * to a smaller size with exact=false, there is no reason to fail the
+ * operation.
+ *
+ * Preallocation mode is ignored since it does not seems useful to fail when
+ * we never change anything.
+ */
+static int coroutine_fn nbd_co_truncate(BlockDriverState *bs, int64_t offset,
+                                        bool exact, PreallocMode prealloc,
+                                        BdrvRequestFlags flags, Error **errp)
+{
+    BDRVNBDState *s = bs->opaque;
+
+    if (offset != s->info.size && exact) {
+        error_setg(errp, "Cannot resize NBD nodes");
+        return -ENOTSUP;
+    }
+
+    if (offset > s->info.size) {
+        error_setg(errp, "Cannot grow NBD nodes");
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
 static int64_t nbd_getlength(BlockDriverState *bs)
 {
     BDRVNBDState *s = bs->opaque;
@@ -2045,6 +2072,7 @@ static BlockDriver bdrv_nbd = {
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
     .bdrv_refresh_limits        = nbd_refresh_limits,
+    .bdrv_co_truncate           = nbd_co_truncate,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_detach_aio_context    = nbd_client_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_client_attach_aio_context,
@@ -2072,6 +2100,7 @@ static BlockDriver bdrv_nbd_tcp = {
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
     .bdrv_refresh_limits        = nbd_refresh_limits,
+    .bdrv_co_truncate           = nbd_co_truncate,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_detach_aio_context    = nbd_client_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_client_attach_aio_context,
@@ -2099,6 +2128,7 @@ static BlockDriver bdrv_nbd_unix = {
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
     .bdrv_refresh_limits        = nbd_refresh_limits,
+    .bdrv_co_truncate           = nbd_co_truncate,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_detach_aio_context    = nbd_client_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_client_attach_aio_context,
diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 851f07e8f8..baeae86d8c 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -1715,7 +1715,7 @@ static int truncate_f(BlockBackend *blk, int argc, char 
**argv)
      * exact=true.  It is better to err on the "emit more errors" side
      * than to be overly permissive.
      */
-    ret = blk_truncate(blk, offset, true, PREALLOC_MODE_OFF, 0, &local_err);
+    ret = blk_truncate(blk, offset, false, PREALLOC_MODE_OFF, 0, &local_err);
     if (ret < 0) {
         error_report_err(local_err);
         return ret;
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#staging