Blame SOURCES/kvm-block-extend-block-commit-to-accept-a-string-for-the.patch

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From c8dda202bd3faf6cdc91834586c8a42ff4a6f762 Mon Sep 17 00:00:00 2001
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From: Jeffrey Cody <jcody@redhat.com>
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Date: Fri, 19 Sep 2014 03:18:57 +0200
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Subject: [PATCH 2/4] block: extend block-commit to accept a string for the backing file
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Message-id: <d49dacc368c02a3cd3d3d9b1d7ea0dc75cc7884a.1411096194.git.jcody@redhat.com>
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Patchwork-id: 61311
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O-Subject: [PATCH qemu-kvm-rhev RHEL7.0.z 2/4] block: extend block-commit to accept a string for the backing file
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Bugzilla: 1122925
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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On some image chains, QEMU may not always be able to resolve the
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filenames properly, when updating the backing file of an image
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after a block commit.
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For instance, certain relative pathnames may fail, or drives may
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have been specified originally by file descriptor (e.g. /dev/fd/???),
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or a relative protocol pathname may have been used.
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In these instances, QEMU may lack the information to be able to make
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the correct choice, but the user or management layer most likely does
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have that knowledge.
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With this extension to the block-commit api, the user is able to change
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the backing file of the overlay image as part of the block-commit
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operation.
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This allows the change to be 'safe', in the sense that if the attempt
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to write the overlay image metadata fails, then the block-commit
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operation returns failure, without disrupting the guest.
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If the commit top is the active layer, then specifying the backing
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file string will be treated as an error (there is no overlay image
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to modify in that case).
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If a backing file string is not specified in the command, the backing
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file string to use is determined in the same manner as it was
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previously.
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Jeff Cody <jcody@redhat.com>
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Reviewed-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit 54e269009099cdc9483be115f1e12d56ad459c5e)
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Conflicts:
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	qapi/block-core.json
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RHEL7 Notes: Conflict is due to qapi json being divided into separate
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             files upstream; downstream in RHEL7 it is still in a single
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             json file.
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Signed-off-by: Jeff Cody <jcody@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 block.c                   |    8 ++++++--
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 block/commit.c            |    9 ++++++---
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 blockdev.c                |    8 +++++++-
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 include/block/block.h     |    3 ++-
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 include/block/block_int.h |    3 ++-
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 qapi-schema.json          |   20 ++++++++++++++++++--
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 qmp-commands.hx           |   19 ++++++++++++++++++-
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 7 files changed, 59 insertions(+), 11 deletions(-)
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diff --git a/block.c b/block.c
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index 058255d..d26e9aa 100644
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--- a/block.c
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+++ b/block.c
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@@ -2319,12 +2319,15 @@ typedef struct BlkIntermediateStates {
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  *
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  * base <- active
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  *
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+ * If backing_file_str is non-NULL, it will be used when modifying top's
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+ * overlay image metadata.
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+ *
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  * Error conditions:
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  *  if active == top, that is considered an error
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  *
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  */
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 int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
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-                           BlockDriverState *base)
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+                           BlockDriverState *base, const char *backing_file_str)
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 {
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     BlockDriverState *intermediate;
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     BlockDriverState *base_bs = NULL;
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@@ -2376,7 +2379,8 @@ int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
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     }
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     /* success - we can delete the intermediate states, and link top->base */
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-    ret = bdrv_change_backing_file(new_top_bs, base_bs->filename,
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+    backing_file_str = backing_file_str ? backing_file_str : base_bs->filename;
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+    ret = bdrv_change_backing_file(new_top_bs, backing_file_str,
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                                    base_bs->drv ? base_bs->drv->format_name : "");
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     if (ret) {
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         goto exit;
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diff --git a/block/commit.c b/block/commit.c
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index e3e395d..b6e1770 100644
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--- a/block/commit.c
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+++ b/block/commit.c
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@@ -37,6 +37,7 @@ typedef struct CommitBlockJob {
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     BlockdevOnError on_error;
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     int base_flags;
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     int orig_overlay_flags;
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+    char *backing_file_str;
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 } CommitBlockJob;
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 static int coroutine_fn commit_populate(BlockDriverState *bs,
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@@ -141,7 +142,7 @@ wait:
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     if (!block_job_is_cancelled(&s->common) && sector_num == end) {
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         /* success */
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-        ret = bdrv_drop_intermediate(active, top, base);
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+        ret = bdrv_drop_intermediate(active, top, base, s->backing_file_str);
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     }
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 exit_free_buf:
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@@ -158,7 +159,7 @@ exit_restore_reopen:
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     if (overlay_bs && s->orig_overlay_flags != bdrv_get_flags(overlay_bs)) {
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         bdrv_reopen(overlay_bs, s->orig_overlay_flags, NULL);
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     }
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-
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+    g_free(s->backing_file_str);
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     block_job_completed(&s->common, ret);
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 }
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@@ -182,7 +183,7 @@ static const BlockJobDriver commit_job_driver = {
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 void commit_start(BlockDriverState *bs, BlockDriverState *base,
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                   BlockDriverState *top, int64_t speed,
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                   BlockdevOnError on_error, BlockDriverCompletionFunc *cb,
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-                  void *opaque, Error **errp)
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+                  void *opaque, const char *backing_file_str, Error **errp)
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 {
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     CommitBlockJob *s;
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     BlockReopenQueue *reopen_queue = NULL;
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@@ -244,6 +245,8 @@ void commit_start(BlockDriverState *bs, BlockDriverState *base,
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     s->base_flags          = orig_base_flags;
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     s->orig_overlay_flags  = orig_overlay_flags;
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+    s->backing_file_str = g_strdup(backing_file_str);
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+
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     s->on_error = on_error;
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     s->common.co = qemu_coroutine_create(commit_run);
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diff --git a/blockdev.c b/blockdev.c
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index a94c9d3..b22b42e 100644
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--- a/blockdev.c
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+++ b/blockdev.c
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@@ -1465,6 +1465,7 @@ void qmp_block_stream(const char *device, bool has_base,
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 void qmp_block_commit(const char *device,
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                       bool has_base, const char *base,
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                       bool has_top, const char *top,
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+                      bool has_backing_file, const char *backing_file,
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                       bool has_speed, int64_t speed,
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                       Error **errp)
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 {
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@@ -1522,11 +1523,16 @@ void qmp_block_commit(const char *device,
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     }
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     if (top_bs == bs) {
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+        if (has_backing_file) {
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+            error_setg(errp, "'backing-file' specified,"
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+                             " but 'top' is the active layer");
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+            return;
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+        }
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         commit_active_start(bs, base_bs, speed, on_error, block_job_cb,
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                             bs, &local_err);
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     } else {
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         commit_start(bs, base_bs, top_bs, speed, on_error, block_job_cb, bs,
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-                    &local_err);
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+                     has_backing_file ? backing_file : NULL, &local_err);
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     }
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     if (local_err != NULL) {
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         error_propagate(errp, local_err);
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diff --git a/include/block/block.h b/include/block/block.h
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index 972c0e7..03b7960 100644
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--- a/include/block/block.h
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+++ b/include/block/block.h
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@@ -256,7 +256,8 @@ int bdrv_change_backing_file(BlockDriverState *bs,
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     const char *backing_file, const char *backing_fmt);
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 void bdrv_register(BlockDriver *bdrv);
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 int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
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-                           BlockDriverState *base);
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+                           BlockDriverState *base,
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+                           const char *backing_file_str);
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 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
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                                     BlockDriverState *bs);
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 BlockDriverState *bdrv_find_base(BlockDriverState *bs);
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diff --git a/include/block/block_int.h b/include/block/block_int.h
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index 53fc98c..e6874b4 100644
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--- a/include/block/block_int.h
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+++ b/include/block/block_int.h
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@@ -389,13 +389,14 @@ void stream_start(BlockDriverState *bs, BlockDriverState *base,
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  * @on_error: The action to take upon error.
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  * @cb: Completion function for the job.
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  * @opaque: Opaque pointer value passed to @cb.
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+ * @backing_file_str: String to use as the backing file in @top's overlay
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  * @errp: Error object.
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  *
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  */
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 void commit_start(BlockDriverState *bs, BlockDriverState *base,
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                  BlockDriverState *top, int64_t speed,
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                  BlockdevOnError on_error, BlockDriverCompletionFunc *cb,
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-                 void *opaque, Error **errp);
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+                 void *opaque, const char *backing_file_str, Error **errp);
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 /**
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  * commit_active_start:
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  * @bs: Active block device to be committed.
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diff --git a/qapi-schema.json b/qapi-schema.json
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index 3768872..100b059 100644
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--- a/qapi-schema.json
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+++ b/qapi-schema.json
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@@ -1842,6 +1842,23 @@
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 #                    which contains the topmost data to be committed down. If
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 #                    not specified, this is the active layer.
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 #
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+# @backing-file:  #optional The backing file string to write into the overlay
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+#                           image of 'top'.  If 'top' is the active layer,
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+#                           specifying a backing file string is an error. This
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+#                           filename is not validated.
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+#
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+#                           If a pathname string is such that it cannot be
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+#                           resolved by QEMU, that means that subsequent QMP or
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+#                           HMP commands must use node-names for the image in
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+#                           question, as filename lookup methods will fail.
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+#
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+#                           If not specified, QEMU will automatically determine
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+#                           the backing file string to use, or error out if
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+#                           there is no obvious choice. Care should be taken
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+#                           when specifying the string, to specify a valid
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+#                           filename or protocol.
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+#                           (Since 2.1)
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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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@@ -1854,7 +1871,6 @@
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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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 # Returns: Nothing on success
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@@ -1869,7 +1885,7 @@
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 ##
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 { 'command': 'block-commit',
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   'data': { 'device': 'str', '*base': 'str', '*top': 'str',
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-            '*speed': 'int' } }
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+            '*backing-file': 'str', '*speed': 'int' } }
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 ##
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 # @drive-mirror
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diff --git a/qmp-commands.hx b/qmp-commands.hx
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index b6b6246..79006c5 100644
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--- a/qmp-commands.hx
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+++ b/qmp-commands.hx
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@@ -1005,7 +1005,7 @@ EQMP
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     {
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         .name       = "block-commit",
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-        .args_type  = "device:B,base:s?,top:s?,speed:o?",
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+        .args_type  = "device:B,base:s?,top:s?,backing-file:s?,speed:o?",
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         .mhandler.cmd_new = qmp_marshal_input_block_commit,
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     },
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@@ -1026,6 +1026,23 @@ Arguments:
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           which contains the topmost data to be committed down. If
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           not specified, this is the active layer. (json-string, optional)
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+- backing-file:     The backing file string to write into the overlay
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+                    image of 'top'.  If 'top' is the active layer,
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+                    specifying a backing file string is an error. This
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+                    filename is not validated.
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+
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+                    If a pathname string is such that it cannot be
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+                    resolved by QEMU, that means that subsequent QMP or
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+                    HMP commands must use node-names for the image in
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+                    question, as filename lookup methods will fail.
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+
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+                    If not specified, QEMU will automatically determine
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+                    the backing file string to use, or error out if
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+                    there is no obvious choice. Care should be taken
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+                    when specifying the string, to specify a valid
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+                    filename or protocol.
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+                    (json-string, optional) (Since 2.1)
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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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-- 
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1.7.1
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