From c8dda202bd3faf6cdc91834586c8a42ff4a6f762 Mon Sep 17 00:00:00 2001

From: Jeffrey Cody <jcody@redhat.com>

Date: Fri, 19 Sep 2014 03:18:57 +0200

Subject: [PATCH 2/4] block: extend block-commit to accept a string for the backing file

Message-id: <d49dacc368c02a3cd3d3d9b1d7ea0dc75cc7884a.1411096194.git.jcody@redhat.com>

Patchwork-id: 61311

O-Subject: [PATCH qemu-kvm-rhev RHEL7.0.z 2/4] block: extend block-commit to accept a string for the backing file

Bugzilla: 1122925

RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

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

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

On some image chains, QEMU may not always be able to resolve the

filenames properly, when updating the backing file of an image

after a block commit.

For instance, certain relative pathnames may fail, or drives may

have been specified originally by file descriptor (e.g. /dev/fd/???),

or a relative protocol pathname may have been used.

In these instances, QEMU may lack the information to be able to make

the correct choice, but the user or management layer most likely does

have that knowledge.

With this extension to the block-commit api, the user is able to change

the backing file of the overlay image as part of the block-commit

operation.

This allows the change to be 'safe', in the sense that if the attempt

to write the overlay image metadata fails, then the block-commit

operation returns failure, without disrupting the guest.

If the commit top is the active layer, then specifying the backing

file string will be treated as an error (there is no overlay image

to modify in that case).

If a backing file string is not specified in the command, the backing

file string to use is determined in the same manner as it was

previously.

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

Signed-off-by: Jeff Cody <jcody@redhat.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

(cherry picked from commit 54e269009099cdc9483be115f1e12d56ad459c5e)

Conflicts:

	qapi/block-core.json

RHEL7 Notes: Conflict is due to qapi json being divided into separate

             files upstream; downstream in RHEL7 it is still in a single

             json file.

Signed-off-by: Jeff Cody <jcody@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 block.c                   |    8 ++++++--

 block/commit.c            |    9 ++++++---

 blockdev.c                |    8 +++++++-

 include/block/block.h     |    3 ++-

 include/block/block_int.h |    3 ++-

 qapi-schema.json          |   20 ++++++++++++++++++--

 qmp-commands.hx           |   19 ++++++++++++++++++-

 7 files changed, 59 insertions(+), 11 deletions(-)

diff --git a/block.c b/block.c

index 058255d..d26e9aa 100644

--- a/block.c

+++ b/block.c

@@ -2319,12 +2319,15 @@ typedef struct BlkIntermediateStates {

  *

  * base <- active

  *

+ * If backing_file_str is non-NULL, it will be used when modifying top's

+ * overlay image metadata.

+ *

  * Error conditions:

  *  if active == top, that is considered an error

  *

  */

 int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,

-                           BlockDriverState *base)

+                           BlockDriverState *base, const char *backing_file_str)

 {

     BlockDriverState *intermediate;

     BlockDriverState *base_bs = NULL;

@@ -2376,7 +2379,8 @@ int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,

     }

     /* success - we can delete the intermediate states, and link top->base */

-    ret = bdrv_change_backing_file(new_top_bs, base_bs->filename,

+    backing_file_str = backing_file_str ? backing_file_str : base_bs->filename;

+    ret = bdrv_change_backing_file(new_top_bs, backing_file_str,

                                    base_bs->drv ? base_bs->drv->format_name : "");

     if (ret) {

         goto exit;

diff --git a/block/commit.c b/block/commit.c

index e3e395d..b6e1770 100644

--- a/block/commit.c

+++ b/block/commit.c

@@ -37,6 +37,7 @@ typedef struct CommitBlockJob {

     BlockdevOnError on_error;

     int base_flags;

     int orig_overlay_flags;

+    char *backing_file_str;

 } CommitBlockJob;

 static int coroutine_fn commit_populate(BlockDriverState *bs,

@@ -141,7 +142,7 @@ wait:

     if (!block_job_is_cancelled(&s->common) && sector_num == end) {

         /* success */

-        ret = bdrv_drop_intermediate(active, top, base);

+        ret = bdrv_drop_intermediate(active, top, base, s->backing_file_str);

     }

 exit_free_buf:

@@ -158,7 +159,7 @@ exit_restore_reopen:

     if (overlay_bs && s->orig_overlay_flags != bdrv_get_flags(overlay_bs)) {

         bdrv_reopen(overlay_bs, s->orig_overlay_flags, NULL);

     }

-

+    g_free(s->backing_file_str);

     block_job_completed(&s->common, ret);

 }

@@ -182,7 +183,7 @@ static const BlockJobDriver commit_job_driver = {

 void commit_start(BlockDriverState *bs, BlockDriverState *base,

                   BlockDriverState *top, int64_t speed,

                   BlockdevOnError on_error, BlockDriverCompletionFunc *cb,

-                  void *opaque, Error **errp)

+                  void *opaque, const char *backing_file_str, Error **errp)

 {

     CommitBlockJob *s;

     BlockReopenQueue *reopen_queue = NULL;

@@ -244,6 +245,8 @@ void commit_start(BlockDriverState *bs, BlockDriverState *base,

     s->base_flags          = orig_base_flags;

     s->orig_overlay_flags  = orig_overlay_flags;

+    s->backing_file_str = g_strdup(backing_file_str);

+

     s->on_error = on_error;

     s->common.co = qemu_coroutine_create(commit_run);

diff --git a/blockdev.c b/blockdev.c

index a94c9d3..b22b42e 100644

--- a/blockdev.c

+++ b/blockdev.c

@@ -1465,6 +1465,7 @@ void qmp_block_stream(const char *device, bool has_base,

 void qmp_block_commit(const char *device,

                       bool has_base, const char *base,

                       bool has_top, const char *top,

+                      bool has_backing_file, const char *backing_file,

                       bool has_speed, int64_t speed,

                       Error **errp)

 {

@@ -1522,11 +1523,16 @@ void qmp_block_commit(const char *device,

     }

     if (top_bs == bs) {

+        if (has_backing_file) {

+            error_setg(errp, "'backing-file' specified,"

+                             " but 'top' is the active layer");

+            return;

+        }

         commit_active_start(bs, base_bs, speed, on_error, block_job_cb,

                             bs, &local_err);

     } else {

         commit_start(bs, base_bs, top_bs, speed, on_error, block_job_cb, bs,

-                    &local_err);

+                     has_backing_file ? backing_file : NULL, &local_err);

     }

     if (local_err != NULL) {

         error_propagate(errp, local_err);

diff --git a/include/block/block.h b/include/block/block.h

index 972c0e7..03b7960 100644

--- a/include/block/block.h

+++ b/include/block/block.h

@@ -256,7 +256,8 @@ int bdrv_change_backing_file(BlockDriverState *bs,

     const char *backing_file, const char *backing_fmt);

 void bdrv_register(BlockDriver *bdrv);

 int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,

-                           BlockDriverState *base);

+                           BlockDriverState *base,

+                           const char *backing_file_str);

 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,

                                     BlockDriverState *bs);

 BlockDriverState *bdrv_find_base(BlockDriverState *bs);

diff --git a/include/block/block_int.h b/include/block/block_int.h

index 53fc98c..e6874b4 100644

--- a/include/block/block_int.h

+++ b/include/block/block_int.h

@@ -389,13 +389,14 @@ void stream_start(BlockDriverState *bs, BlockDriverState *base,

  * @on_error: The action to take upon error.

  * @cb: Completion function for the job.

  * @opaque: Opaque pointer value passed to @cb.

+ * @backing_file_str: String to use as the backing file in @top's overlay

  * @errp: Error object.

  *

  */

 void commit_start(BlockDriverState *bs, BlockDriverState *base,

                  BlockDriverState *top, int64_t speed,

                  BlockdevOnError on_error, BlockDriverCompletionFunc *cb,

-                 void *opaque, Error **errp);

+                 void *opaque, const char *backing_file_str, Error **errp);

 /**

  * commit_active_start:

  * @bs: Active block device to be committed.

diff --git a/qapi-schema.json b/qapi-schema.json

index 3768872..100b059 100644

--- a/qapi-schema.json

+++ b/qapi-schema.json

@@ -1842,6 +1842,23 @@

 #                    which contains the topmost data to be committed down. If

 #                    not specified, this is the active layer.

 #

+# @backing-file:  #optional The backing file string to write into the overlay

+#                           image of 'top'.  If 'top' is the active layer,

+#                           specifying a backing file string is an error. This

+#                           filename is not validated.

+#

+#                           If a pathname string is such that it cannot be

+#                           resolved by QEMU, that means that subsequent QMP or

+#                           HMP commands must use node-names for the image in

+#                           question, as filename lookup methods will fail.

+#

+#                           If not specified, QEMU will automatically determine

+#                           the backing file string to use, or error out if

+#                           there is no obvious choice. Care should be taken

+#                           when specifying the string, to specify a valid

+#                           filename or protocol.

+#                           (Since 2.1)

+#

 #                    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

@@ -1854,7 +1871,6 @@

 #                    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

 #

 # Returns: Nothing on success

@@ -1869,7 +1885,7 @@

 ##

 { 'command': 'block-commit',

   'data': { 'device': 'str', '*base': 'str', '*top': 'str',

-            '*speed': 'int' } }

+            '*backing-file': 'str', '*speed': 'int' } }

 ##

 # @drive-mirror

diff --git a/qmp-commands.hx b/qmp-commands.hx

index b6b6246..79006c5 100644

--- a/qmp-commands.hx

+++ b/qmp-commands.hx

@@ -1005,7 +1005,7 @@ EQMP

     {

         .name       = "block-commit",

-        .args_type  = "device:B,base:s?,top:s?,speed:o?",

+        .args_type  = "device:B,base:s?,top:s?,backing-file:s?,speed:o?",

         .mhandler.cmd_new = qmp_marshal_input_block_commit,

     },

@@ -1026,6 +1026,23 @@ Arguments:

           which contains the topmost data to be committed down. If

           not specified, this is the active layer. (json-string, optional)

+- backing-file:     The backing file string to write into the overlay

+                    image of 'top'.  If 'top' is the active layer,

+                    specifying a backing file string is an error. This

+                    filename is not validated.

+

+                    If a pathname string is such that it cannot be

+                    resolved by QEMU, that means that subsequent QMP or

+                    HMP commands must use node-names for the image in

+                    question, as filename lookup methods will fail.

+

+                    If not specified, QEMU will automatically determine

+                    the backing file string to use, or error out if

+                    there is no obvious choice. Care should be taken

+                    when specifying the string, to specify a valid

+                    filename or protocol.

+                    (json-string, optional) (Since 2.1)

+

           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

-- 

1.7.1