Patchwork [v4,17/21] docs, qapi: document qemu-img map

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Submitter Paolo Bonzini
Date Aug. 29, 2013, 2 p.m.
Message ID <1377784821-29561-18-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/270844/
State New
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Comments

Paolo Bonzini - Aug. 29, 2013, 2 p.m.
Eric Blake also requested including the output in qapi-schema.json,
so that it is published through the introspection mechanism.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qapi-schema.json | 29 +++++++++++++++++++++++++++++
 qemu-img.texi    | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+)
Eric Blake - Aug. 29, 2013, 3:31 p.m.
On 08/29/2013 08:00 AM, Paolo Bonzini wrote:
> Eric Blake also requested including the output in qapi-schema.json,
> so that it is published through the introspection mechanism.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  qapi-schema.json | 29 +++++++++++++++++++++++++++++
>  qemu-img.texi    | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 84 insertions(+)
> 
> +# @offset: if present, the image file stores the data for this range in
> +#          raw format at the given offset.
> +#
> +# Since 1.6

We missed that boat.  1.7 now.

> +##
> +{ 'type': 'BlockDeviceMapEntry',
> +  'data': { 'start': 'int', 'length': 'int', 'depth': 'int', 'zero': 'bool',
> +            'data': 'bool', '*offset': 'int' } }

Fix that, and you can add:

Reviewed-by: Eric Blake <eblake@redhat.com>

Patch

diff --git a/qapi-schema.json b/qapi-schema.json
index a51f7d2..979f0c1 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -813,6 +813,35 @@ 
 { 'enum': 'BlockDeviceIoStatus', 'data': [ 'ok', 'failed', 'nospace' ] }
 
 ##
+# @BlockDeviceMapEntry:
+#
+# Entry in the metadata map of the device (returned by "qemu-img map")
+#
+# @start: Offset in the image of the first byte described by this entry
+#         (in bytes)
+#
+# @length: Length of the range described by this entry (in bytes)
+#
+# @depth: Number of layers (0 = top image, 1 = top image's backing file, etc.)
+#         before reaching one for which the range is allocated.  The value is
+#         in the range 0 to the depth of the image chain - 1.
+#
+# @zero: the sectors in this range read as zeros
+#
+# @data: reading the image will actually read data from a file (in particular,
+#        if @offset is present this means that the sectors are not simply
+#        preallocated, but contain actual data in raw format)
+#
+# @offset: if present, the image file stores the data for this range in
+#          raw format at the given offset.
+#
+# Since 1.6
+##
+{ 'type': 'BlockDeviceMapEntry',
+  'data': { 'start': 'int', 'length': 'int', 'depth': 'int', 'zero': 'bool',
+            'data': 'bool', '*offset': 'int' } }
+
+##
 # @BlockDirtyInfo:
 #
 # Block dirty bitmap information.
diff --git a/qemu-img.texi b/qemu-img.texi
index 69f1bda..8364fa1 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -213,6 +213,61 @@  To enumerate information about each disk image in the above chain, starting from
 qemu-img info --backing-chain snap2.qcow2
 @end example
 
+@item map [-f @var{fmt}] [--output=@var{ofmt}] @var{filename}
+
+Dump the metadata of image @var{filename} and its backing file chain.
+In particular, this commands dumps the allocation state of every sector
+of @var{filename}, together with the topmost file that allocates it in
+the backing file chain.
+
+Two option formats are possible.  The default format (@code{human})
+only dumps known-nonzero areas of the file.  Known-zero parts of the
+file are omitted altogether, and likewise for parts that are not allocated
+throughout the chain.  @command{qemu-img} output will identify a file
+from where the data can be read, and the offset in the file.  Each line
+will include four fields, the first three of which are hexadecimal
+numbers.  For example the first line of:
+@example
+Offset          Length          Mapped to       File
+0               0x20000         0x50000         /tmp/overlay.qcow2
+0x100000        0x10000         0x95380000      /tmp/backing.qcow2
+@end example
+@noindent
+means that 0x20000 (131072) bytes starting at offset 0 in the image are
+available in /tmp/overlay.qcow2 (opened in @code{raw} format) starting
+at offset 0x50000 (327680).  Data that is compressed, encrypted, or
+otherwise not available in raw format will cause an error if @code{human}
+format is in use.  Note that file names can include newlines, thus it is
+not safe to parse this output format in scripts.
+
+The alternative format @code{json} will return an array of dictionaries
+in JSON format.  It will include similar information in
+the @code{start}, @code{length}, @code{offset} fields;
+it will also include other more specific information:
+@itemize @minus
+@item
+whether the sectors contain actual data or not (boolean field @code{data};
+if false, the sectors are either unallocated or stored as optimized
+all-zero clusters);
+
+@item
+whether the data is known to read as zero (boolean field @code{zero});
+
+@item
+in order to make the output shorter, the target file is expressed as
+a @code{depth}; for example, a depth of 2 refers to the backing file
+of the backing file of @var{filename}.
+@end itemize
+
+In JSON format, the @code{offset} field is optional; it is absent in
+cases where @code{human} format would omit the entry or exit with an error.
+If @code{data} is false and the @code{offset} field is present, the
+corresponding sectors in the file are not yet in use, but they are
+preallocated.
+
+For more information, consult @file{include/block/block.h} in QEMU's
+source code.
+
 @item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename}
 
 List, apply, create or delete snapshots in image @var{filename}.