qemu-img info: Optionally show block limits

Add a new --limits option to 'qemu-img info' that displays the block
limits for the image and all of its children, making the information
more accessible for human users than in QMP. This option is not enabled
by default because it can be a lot of output that isn't usually relevant
if you're not specifically trying to diagnose some I/O problem.

This makes the same information automatically also available in HMP
'info block -v'.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20251024123041.51254-4-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

docs/tools/qemu-img.rst

@@ -503,7 +503,7 @@ Command description:
 
   The size syntax is similar to :manpage:`dd(1)`'s size syntax.
 
-.. option:: info [--object OBJECTDEF] [--image-opts] [-f FMT] [--output=OFMT] [--backing-chain] [-U] FILENAME
+.. option:: info [--object OBJECTDEF] [--image-opts] [-f FMT] [--output=OFMT] [--backing-chain] [--limits] [-U] FILENAME
 
   Give information about the disk image *FILENAME*. Use it in
   particular to know the size reserved on disk which can be different
@@ -571,6 +571,10 @@ Command description:
     ``ImageInfoSpecific*`` QAPI object (e.g. ``ImageInfoSpecificQCow2``
     for qcow2 images).
 
+  *Block limits*
+    The block limits for I/O that QEMU detected for the image.
+    This information is only shown if the ``--limits`` option was specified.
+
 .. option:: map [--object OBJECTDEF] [--image-opts] [-f FMT] [--start-offset=OFFSET] [--max-length=LEN] [--output=OFMT] [-U] FILENAME
 
   Dump the metadata of image *FILENAME* and its backing file chain.