Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2020-02-20' into staging

Block patches:
- qemu-img convert: New --target-is-zero parameter
- qcow2: Specify non-default compression type flag
- optionally flat output for query-named-block-nodes
- some fixes
- pseudo-creation of images on block devices is now done by a generic
  block layer function

# gpg: Signature made Thu 20 Feb 2020 16:05:34 GMT
# gpg:                using RSA key 91BEB60A30DB3E8857D11829F407DB0061D5CF40
# gpg:                issuer "mreitz@redhat.com"
# gpg: Good signature from "Max Reitz <mreitz@redhat.com>" [full]
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* remotes/maxreitz/tags/pull-block-2020-02-20:
  iotests: Test snapshot -l field separation
  block: Fix VM size field width in snapshot dump
  iotests: Test convert -n -B to backing-less target
  qemu-img: Fix convert -n -B for backing-less targets
  iotests: Add test for image creation fallback
  iscsi: Drop iscsi_co_create_opts()
  file-posix: Drop hdev_co_create_opts()
  block: Generic file creation fallback
  block/nbd: Fix hang in .bdrv_close()
  iotests/279: Fix for non-qcow2 formats
  block/backup-top: fix flags handling
  block: always fill entire LUKS header space with zeros
  qemu-img: Add --target-is-zero to convert
  qapi: Allow getting flat output from 'query-named-block-nodes'
  iotests/147: Fix drive parameters
  iotests: Remove the superfluous 2nd check for the availability of quorum
  docs: qcow2: introduce compression type feature
  docs: improve qcow2 spec about extending image header

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

2 files changed, 68 insertions, 5 deletions

diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index af5711e..5597e24 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -79,9 +79,9 @@ The first cluster of a qcow2 image contains the file header:
                     Offset into the image file at which the snapshot table
                     starts. Must be aligned to a cluster boundary.
 
-If the version is 3 or higher, the header has the following additional fields.
-For version 2, the values are assumed to be zero, unless specified otherwise
-in the description of a field.
+For version 2, the header is exactly 72 bytes in length, and finishes here.
+For version 3 or higher, the header length is at least 104 bytes, including
+the next fields through header_length.
 
          72 -  79:  incompatible_features
                     Bitmask of incompatible features. An implementation must
@@ -109,7 +109,12 @@ in the description of a field.
                                 An External Data File Name header extension may
                                 be present if this bit is set.
 
-                    Bits 3-63:  Reserved (set to 0)
+                    Bit 3:      Compression type bit.  If this bit is set,
+                                a non-default compression is used for compressed
+                                clusters. The compression_type field must be
+                                present and not zero.
+
+                    Bits 4-63:  Reserved (set to 0)
 
          80 -  87:  compatible_features
                     Bitmask of compatible features. An implementation can
@@ -164,6 +169,57 @@ in the description of a field.
         100 - 103:  header_length
                     Length of the header structure in bytes. For version 2
                     images, the length is always assumed to be 72 bytes.
+                    For version 3 it's at least 104 bytes and must be a multiple
+                    of 8.
+
+
+=== Additional fields (version 3 and higher) ===
+
+In general, these fields are optional and may be safely ignored by the software,
+as well as filled by zeros (which is equal to field absence), if software needs
+to set field B, but does not care about field A which precedes B. More
+formally, additional fields have the following compatibility rules:
+
+1. If the value of the additional field must not be ignored for correct
+handling of the file, it will be accompanied by a corresponding incompatible
+feature bit.
+
+2. If there are no unrecognized incompatible feature bits set, an unknown
+additional field may be safely ignored other than preserving its value when
+rewriting the image header.
+
+3. An explicit value of 0 will have the same behavior as when the field is not
+present*, if not altered by a specific incompatible bit.
+
+*. A field is considered not present when header_length is less than or equal
+to the field's offset. Also, all additional fields are not present for
+version 2.
+
+              104:  compression_type
+
+                    Defines the compression method used for compressed clusters.
+                    All compressed clusters in an image use the same compression
+                    type.
+
+                    If the incompatible bit "Compression type" is set: the field
+                    must be present and non-zero (which means non-zlib
+                    compression type). Otherwise, this field must not be present
+                    or must be zero (which means zlib).
+
+                    Available compression type values:
+                        0: zlib <https://www.zlib.net/>
+
+
+=== Header padding ===
+
+@header_length must be a multiple of 8, which means that if the end of the last
+additional field is not aligned, some padding is needed. This padding must be
+zeroed, so that if some existing (or future) additional field will fall into
+the padding, it will be interpreted accordingly to point [3.] of the previous
+paragraph, i.e.  in the same manner as when this field is not present.
+
+
+=== Header extensions ===
 
 Directly after the image header, optional sections called header extensions can
 be stored. Each extension has a structure like the following:
diff --git a/docs/interop/qemu-img.rst b/docs/interop/qemu-img.rst
index 42e4451..5f40137 100644
--- a/docs/interop/qemu-img.rst
+++ b/docs/interop/qemu-img.rst
@@ -214,6 +214,13 @@ Parameters to convert subcommand:
   will still be printed.  Areas that cannot be read from the source will be
   treated as containing only zeroes.
 
+.. option:: --target-is-zero
+
+  Assume that reading the destination image will always return
+  zeros. This parameter is mutually exclusive with a destination image
+  that has a backing file. It is required to also use the ``-n``
+  parameter to skip image creation.
+
 Parameters to dd subcommand:
 
 .. program:: qemu-img-dd
@@ -366,7 +373,7 @@ Command description:
   4
     Error on reading data
 
-.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
+.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
 
   Convert the disk image *FILENAME* or a snapshot *SNAPSHOT_PARAM*
   to disk image *OUTPUT_FILENAME* using format *OUTPUT_FMT*. It can