Thanks, that looks good.
I can confirm the test and updated the bug description.
I'll check backportability for 2.11 and 2.12 later today after I have added 
2.11.2

** Description changed:

+ [Impact]
+ 
+  * During qemu-io VM disk read, there is a possibility for qemu-io to 
+    abort crashing the process running. This also crashes the VM the read 
+    is running against.
+ 
+  * Backport upstream fix from
+ 
+ [Test Case]
+ 
+  * Steps to reproduce outside of a block pull:
+     $ qemu-img create -f qcow2 test 1024 2>&1
+     $ qemu-io -f qcow2 -C -c 'read 0 1024' test
+ 
+     Without the fix:
+     Error:
+     qemu-io: /build/qemu-Eap4uc/qemu-2.11+dfsg/block/io.c:1042: 
+     bdrv_co_do_copy_on_readv: Assertion `skip_bytes < pnum' failed.
+     Aborted (core dumped)
+     
+     With fix:
+     read 1024/1024 bytes at offset 0
+     1 KiB, 1 ops; 0.0045 sec (220.604 KiB/sec and 220.6045 ops/sec)
+ 
+ [Regression Potential]
+ 
+  * The change is small and unchanged since two releases which indicates it 
+    is rather stable. The only thing it adds is a safety check on ret&&pnum 
+    being zero to leave the loop.
+    The only related regression I could think of is leaving the loop too 
+    early, but when pnum==0 it has nothing more to write, so there should 
+    be no issue to leave.
+ 
+ [Other Info]
+  
+  * n/a
+ 
+ ---
+ 
  When attempting to do a blockpull the following error occurs and the VM
  crashes.
  
  qemu-system-x86_64: /build/qemu-Eap4uc/qemu-2.11+dfsg/block/io.c:1042: 
bdrv_co_do_copy_on_readv: Assertion `skip_bytes < pnum' failed.
  2019-02-17 17:38:27.820+0000: shutting down, reason=crashed
  
  This appears to be fixed upstream.
  https://patchwork.kernel.org/patch/10512135/
  https://github.com/qemu/qemu/commit/b0ddcbbb36a66a605eb232b905cb49b1cc72e74e

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https://bugs.launchpad.net/bugs/1818264

Title:
  QEMU 2.11.1 VM crash when performing block pull.
  bdrv_co_do_copy_on_readv

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