From: Peter Krempa <pkrempa@redhat.com>

Use the new VIR_DOMAIN_BLOCK_RESIZE_EXTEND to prevent accidentally
shrinking a disk and thus destroying data.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
---
 docs/manpages/virsh.rst | 7 ++++++-
 tools/virsh-domain.c    | 7 +++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
index 4b8bbec7d6..80b0ea14a8 100644
--- a/docs/manpages/virsh.rst
+++ b/docs/manpages/virsh.rst
@@ -1642,7 +1642,7 @@ blockresize

 ::

-   blockresize domain path ([size] | [--capacity])
+   blockresize domain path ([size] | [--capacity]) [--extend]

 Resize a block device of domain while the domain is running, *path*
 specifies the absolute path of the block device; it corresponds
@@ -1650,6 +1650,11 @@ to a unique target name (<target dev='name'/>) or source file (<source
 file='name'/>) for one of the disk devices attached to *domain* (see
 also ``domblklist`` for listing these names).

+The *--extend* flag instructs the hypervisor to ensure that the new size isn't
+smaller than the old size, thus prevents (accidental) shrinking of the block
+device which may lead to data loss. Users are encouraged to always use this
+flag unless communicating with an older hypervisor.
+
 For image formats without metadata (raw) stored inside fixed-size storage (e.g.
 block devices) the --capacity flag can be used to resize the device to the
 full size of the backing device.
diff --git a/tools/virsh-domain.c b/tools/virsh-domain.c
index a17c8b42e2..08a1ce3953 100644
--- a/tools/virsh-domain.c
+++ b/tools/virsh-domain.c
@@ -3339,6 +3339,10 @@ static const vshCmdOptDef opts_blockresize[] = {
      .type = VSH_OT_BOOL,
      .help = N_("resize to capacity of source (block device)")
     },
+    {.name = "extend",
+     .type = VSH_OT_BOOL,
+     .help = N_("ensure that the new size is larger than actual capacity (prevent shrink)")
+    },
     {.name = NULL}
 };

@@ -3352,6 +3356,9 @@ cmdBlockresize(vshControl *ctl, const vshCmd *cmd)

     VSH_ALTERNATIVE_OPTIONS("size", "capacity");

+    if (vshCommandOptBool(cmd, "extend"))
+        flags |= VIR_DOMAIN_BLOCK_RESIZE_EXTEND;
+
     if (vshCommandOptString(ctl, cmd, "path", (const char **) &path) < 0)
         return false;

-- 
2.53.0