Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2019-02-04' into staging

nbd patches for 2019-02-04

- deprecate 'qemu-nbd --partition'
- preparation for NBD reconnect, including better logging of read errors

# gpg: Signature made Tue 05 Feb 2019 03:50:56 GMT
# gpg:                using RSA key A7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>" [full]
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>" [full]
# gpg:                 aka "[jpeg image of size 6874]" [full]
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-nbd-2019-02-04:
  block/nbd-client: rename read_reply_co to connection_co
  block/nbd-client: don't check ioc
  block/nbd-client: fix nbd_reply_chunk_iter_receive
  block/nbd-client: split connection from initialization
  block/nbd: move connection code from block/nbd to block/nbd-client
  block/nbd-client: split channel errors from export errors
  nbd: generalize usage of nbd_read
  qemu-nbd: Deprecate qemu-nbd --partition

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
index 9cc20b365c..8a6174df0c 100644
--- a/qemu-deprecated.texi
+++ b/qemu-deprecated.texi
@@ -160,3 +160,36 @@ Example of legacy encoding:
 The above, converted to the current supported format:
 
 @code{json:@{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"@}}
+
+@section Related binaries
+
+@subsection qemu-nbd --partition (since 4.0.0)
+
+The ``qemu-nbd --partition $digit'' code (also spelled @option{-P})
+can only handle MBR partitions, and has never correctly handled
+logical partitions beyond partition 5.  If you know the offset and
+length of the partition (perhaps by using @code{sfdisk} within the
+guest), you can achieve the effect of exporting just that subset of
+the disk by use of the @option{--image-opts} option with a raw
+blockdev using the @code{offset} and @code{size} parameters layered on
+top of any other existing blockdev. For example, if partition 1 is
+100MiB long starting at 1MiB, the old command:
+
+@code{qemu-nbd -t -P 1 -f qcow2 file.qcow2}
+
+can be rewritten as:
+
+@code{qemu-nbd -t --image-opts driver=raw,offset=1M,size=100M,file.driver=qcow2,file.backing.driver=file,file.backing.filename=file.qcow2}
+
+Alternatively, the @code{nbdkit} project provides a more powerful
+partition filter on top of its nbd plugin, which can be used to select
+an arbitrary MBR or GPT partition on top of any other full-image NBD
+export.  Using this to rewrite the above example results in:
+
+@code{qemu-nbd -t -k /tmp/sock -f qcow2 file.qcow2 &}
+@code{nbdkit -f --filter=partition nbd socket=/tmp/sock partition=1}
+
+Note that if you are exposing the export via /dev/nbd0, it is easier
+to just export the entire image and then mount only /dev/nbd0p1 than
+it is to reinvoke @command{qemu-nbd -c /dev/nbd0} limited to just a
+subset of the image.