Blob Blame Raw
From c7c21ebc0dcddd666c616e161b0f9bbb4ade9cf4 Mon Sep 17 00:00:00 2001
From: Jeffrey Cody <jcody@redhat.com>
Date: Tue, 11 Feb 2014 16:14:27 +0100
Subject: [PATCH 21/28] block: update block commit documentation regarding image truncation

RH-Author: Jeffrey Cody <jcody@redhat.com>
Message-id: <d4d68c21d4b8936f3bcdc442abe0425e01352167.1392134912.git.jcody@redhat.com>
Patchwork-id: 57217
O-Subject: [RHEL7 qemu-kvm PATCH 3/6] block: update block commit documentation regarding image truncation
Bugzilla: 1047254
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Markus Armbruster <armbru@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

This updates the documentation for commiting snapshot images.
Specifically, this highlights what happens when the base image
is either smaller or larger than the snapshot image being committed.

In the case of the base image being smaller, it is resized to the
larger size of the snapshot image.  In the case of the base image
being larger, it is not resized automatically, but once the commit
has completed it is safe for the user to truncate the base image.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 37222900743962e146a82b7077a18c3f39859a19)

Conflicts:
	qmp-commands.hx

RHEL7 Notes: Conflict is due to 2 things: 1) drive-backup
             not present in RHEL7, and 2) the block job
             differentiation #ifdefs.
---
 hmp-commands.hx  |  5 +++++
 qapi-schema.json |  7 +++++++
 qemu-img.texi    |  7 ++++++-
 qmp-commands.hx  | 40 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 58 insertions(+), 1 deletion(-)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hmp-commands.hx  |    5 +++++
 qapi-schema.json |    7 +++++++
 qemu-img.texi    |    7 ++++++-
 qmp-commands.hx  |   40 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 58 insertions(+), 1 deletions(-)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index 8e08ebf..467dd70 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -35,6 +35,11 @@ STEXI
 @item commit
 @findex commit
 Commit changes to the disk images (if -snapshot is used) or backing files.
+If the backing file is smaller than the snapshot, then the backing file will be
+resized to be the same size as the snapshot.  If the snapshot is smaller than
+the backing file, the backing file will not be truncated.  If you want the
+backing file to match the size of the smaller snapshot, you can safely truncate
+it yourself once the commit operation successfully completes.
 ETEXI
 
     {
diff --git a/qapi-schema.json b/qapi-schema.json
index 8b257e2..017b3b7 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1846,6 +1846,13 @@
 #                    user needs to complete the job with the block-job-complete
 #                    command after getting the ready event. (Since 2.0)
 #
+#                    If the base image is smaller than top, then the base image
+#                    will be resized to be the same size as top.  If top is
+#                    smaller than the base image, the base will not be
+#                    truncated.  If you want the base image size to match the
+#                    size of the smaller top, you can safely truncate it
+#                    yourself once the commit operation successfully completes.
+#
 #
 # @speed:  #optional the maximum speed, in bytes per second
 #
diff --git a/qemu-img.texi b/qemu-img.texi
index 1078791..d75a780 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -136,7 +136,12 @@ it doesn't need to be specified separately in this case.
 
 @item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
 
-Commit the changes recorded in @var{filename} in its base image.
+Commit the changes recorded in @var{filename} in its base image or backing file.
+If the backing file is smaller than the snapshot, then the backing file will be
+resized to be the same size as the snapshot.  If the snapshot is smaller than
+the backing file, the backing file will not be truncated.  If you want the
+backing file to match the size of the smaller snapshot, you can safely truncate
+it yourself once the commit operation successfully completes.
 
 @item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2}
 
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 7a1bfd4..08a01ee 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -1008,6 +1008,46 @@ EQMP
         .args_type  = "device:B,base:s?,top:s,speed:o?",
         .mhandler.cmd_new = qmp_marshal_input_block_commit,
     },
+
+SQMP
+block-commit
+------------
+
+Live commit of data from overlay image nodes into backing nodes - i.e., writes
+data between 'top' and 'base' into 'base'.
+
+Arguments:
+
+- "device": The device's ID, must be unique (json-string)
+- "base": The file name of the backing image to write data into.
+          If not specified, this is the deepest backing image
+          (json-string, optional)
+- "top":  The file name of the backing image within the image chain,
+          which contains the topmost data to be committed down.
+
+          If top == base, that is an error.
+          If top == active, the job will not be completed by itself,
+          user needs to complete the job with the block-job-complete
+          command after getting the ready event. (Since 2.0)
+
+          If the base image is smaller than top, then the base image
+          will be resized to be the same size as top.  If top is
+          smaller than the base image, the base will not be
+          truncated.  If you want the base image size to match the
+          size of the smaller top, you can safely truncate it
+          yourself once the commit operation successfully completes.
+          (json-string)
+- "speed":  the maximum speed, in bytes per second (json-int, optional)
+
+
+Example:
+
+-> { "execute": "block-commit", "arguments": { "device": "virtio0",
+                                              "top": "/tmp/snap1.qcow2" } }
+<- { "return": {} }
+
+EQMP
+
 #endif
 
     {
-- 
1.7.1