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From c7c21ebc0dcddd666c616e161b0f9bbb4ade9cf4 Mon Sep 17 00:00:00 2001
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From: Jeffrey Cody <jcody@redhat.com>
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Date: Tue, 11 Feb 2014 16:14:27 +0100
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Subject: [PATCH 21/28] block: update block commit documentation regarding image truncation
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RH-Author: Jeffrey Cody <jcody@redhat.com>
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Message-id: <d4d68c21d4b8936f3bcdc442abe0425e01352167.1392134912.git.jcody@redhat.com>
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Patchwork-id: 57217
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O-Subject: [RHEL7 qemu-kvm PATCH 3/6] block: update block commit documentation regarding image truncation
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Bugzilla: 1047254
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Acked-by: Markus Armbruster <armbru@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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This updates the documentation for commiting snapshot images.
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Specifically, this highlights what happens when the base image
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is either smaller or larger than the snapshot image being committed.
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In the case of the base image being smaller, it is resized to the
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larger size of the snapshot image.  In the case of the base image
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being larger, it is not resized automatically, but once the commit
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has completed it is safe for the user to truncate the base image.
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Signed-off-by: Jeff Cody <jcody@redhat.com>
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Reviewed-by: Fam Zheng <famz@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 37222900743962e146a82b7077a18c3f39859a19)
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Conflicts:
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	qmp-commands.hx
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RHEL7 Notes: Conflict is due to 2 things: 1) drive-backup
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             not present in RHEL7, and 2) the block job
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             differentiation #ifdefs.
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---
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 hmp-commands.hx  |  5 +++++
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 qapi-schema.json |  7 +++++++
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 qemu-img.texi    |  7 ++++++-
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 qmp-commands.hx  | 40 ++++++++++++++++++++++++++++++++++++++++
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 4 files changed, 58 insertions(+), 1 deletion(-)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 hmp-commands.hx  |    5 +++++
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 qapi-schema.json |    7 +++++++
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 qemu-img.texi    |    7 ++++++-
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 qmp-commands.hx  |   40 ++++++++++++++++++++++++++++++++++++++++
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 4 files changed, 58 insertions(+), 1 deletions(-)
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diff --git a/hmp-commands.hx b/hmp-commands.hx
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index 8e08ebf..467dd70 100644
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--- a/hmp-commands.hx
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+++ b/hmp-commands.hx
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@@ -35,6 +35,11 @@ STEXI
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 @item commit
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 @findex commit
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 Commit changes to the disk images (if -snapshot is used) or backing files.
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+If the backing file is smaller than the snapshot, then the backing file will be
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+resized to be the same size as the snapshot.  If the snapshot is smaller than
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+the backing file, the backing file will not be truncated.  If you want the
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+backing file to match the size of the smaller snapshot, you can safely truncate
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+it yourself once the commit operation successfully completes.
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 ETEXI
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     {
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diff --git a/qapi-schema.json b/qapi-schema.json
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index 8b257e2..017b3b7 100644
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--- a/qapi-schema.json
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+++ b/qapi-schema.json
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@@ -1846,6 +1846,13 @@
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 #                    user needs to complete the job with the block-job-complete
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 #                    command after getting the ready event. (Since 2.0)
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 #
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+#                    If the base image is smaller than top, then the base image
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+#                    will be resized to be the same size as top.  If top is
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+#                    smaller than the base image, the base will not be
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+#                    truncated.  If you want the base image size to match the
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+#                    size of the smaller top, you can safely truncate it
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+#                    yourself once the commit operation successfully completes.
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+#
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 #
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 # @speed:  #optional the maximum speed, in bytes per second
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 #
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diff --git a/qemu-img.texi b/qemu-img.texi
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index 1078791..d75a780 100644
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--- a/qemu-img.texi
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+++ b/qemu-img.texi
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@@ -136,7 +136,12 @@ it doesn't need to be specified separately in this case.
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 @item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
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-Commit the changes recorded in @var{filename} in its base image.
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+Commit the changes recorded in @var{filename} in its base image or backing file.
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+If the backing file is smaller than the snapshot, then the backing file will be
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+resized to be the same size as the snapshot.  If the snapshot is smaller than
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+the backing file, the backing file will not be truncated.  If you want the
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+backing file to match the size of the smaller snapshot, you can safely truncate
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+it yourself once the commit operation successfully completes.
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 @item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2}
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diff --git a/qmp-commands.hx b/qmp-commands.hx
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index 7a1bfd4..08a01ee 100644
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--- a/qmp-commands.hx
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+++ b/qmp-commands.hx
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@@ -1008,6 +1008,46 @@ EQMP
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         .args_type  = "device:B,base:s?,top:s,speed:o?",
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         .mhandler.cmd_new = qmp_marshal_input_block_commit,
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     },
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+
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+SQMP
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+block-commit
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+------------
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+
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+Live commit of data from overlay image nodes into backing nodes - i.e., writes
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+data between 'top' and 'base' into 'base'.
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+
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+Arguments:
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+
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+- "device": The device's ID, must be unique (json-string)
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+- "base": The file name of the backing image to write data into.
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+          If not specified, this is the deepest backing image
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+          (json-string, optional)
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+- "top":  The file name of the backing image within the image chain,
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+          which contains the topmost data to be committed down.
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+
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+          If top == base, that is an error.
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+          If top == active, the job will not be completed by itself,
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+          user needs to complete the job with the block-job-complete
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+          command after getting the ready event. (Since 2.0)
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+
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+          If the base image is smaller than top, then the base image
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+          will be resized to be the same size as top.  If top is
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+          smaller than the base image, the base will not be
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+          truncated.  If you want the base image size to match the
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+          size of the smaller top, you can safely truncate it
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+          yourself once the commit operation successfully completes.
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+          (json-string)
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+- "speed":  the maximum speed, in bytes per second (json-int, optional)
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+
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+
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+Example:
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+
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+-> { "execute": "block-commit", "arguments": { "device": "virtio0",
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+                                              "top": "/tmp/snap1.qcow2" } }
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+<- { "return": {} }
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+
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+EQMP
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+
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 #endif
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     {
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-- 
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1.7.1
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