Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
- Original Message - From: Paolo Bonzini pbonz...@redhat.com Cc: Federico Simoncelli fsimo...@redhat.com, kw...@redhat.com, mtosa...@redhat.com, qemu-devel@nongnu.org Sent: Thursday, February 23, 2012 8:38:55 AM Subject: Re: [PATCH 3/3] Add nocreate option to snapshot_blkdev On 02/23/2012 08:19 AM, Paolo Bonzini wrote: Signed-off-by: Federico Simoncelli fsimo...@redhat.com What is the usecase, and how can this be tested? Oops, you explained it in part 0. Step 5 - Final Switch to Destination VM1 is now able to switch to the destination for both read and write operations. [src/hd0base] - [src/hd0snap1] = VM1(read-write) (qemu) snapshot_blkdev -n ide0-hd0 /tmp/dst/hd0snap1.qcow2 It seems to me that reusing the snapshot_blkdev command is a bit of a misnomer. It also forces you to use format autodetection for the destination in the blkmirror phase. I see two possibilities: 1) you can make a new command block_reopen; this fixes only the naming problem. 2) you can hide the new format behind a new command to be used like this: block_migrate --mirror ide-hd0 /tmp/dst/hd0snap1.qcow2 ... block_migrate --switch ide-hd0 This leave the possibility to specify the format in the future: block_migrate --mirror ide-hd0 /tmp/dst/hd0snap1.qcow2 qcow2 And we could have another sub-command block_mirror --stream ide-hd0 /tmp/dst/hd0.raw to migrate block devices without shared storage and without an intermediate snapshot. I agree on the fact that using snapshot_blkdev is a misnomer but at the same time I like very much how blkmirror is modular and it can be used as a regular image filename. I'm worried that making it explicit with a --mirror option would take away its flexibility. What about adding block_reopen and extending the blkmirror string: (qemu) block_reopen ide-hd0 \ blkmirror:qcow2:/tmp/src/hd0snap1.qcow2:/tmp/dst/hd0snap1.qcow2 so that the format is passed as first argument (and if it's empty we would use the auto-detection). -- Federico
Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
On 02/23/2012 10:39 AM, Federico Simoncelli wrote: I agree on the fact that using snapshot_blkdev is a misnomer but at the same time I like very much how blkmirror is modular and it can be used as a regular image filename. True, on the other hand if we add this we will have to keep it forever. I'm worried that blkmirror does not satisfy _all_ mirroring needs, for example you cannot use block_stream to copy from the source to the destination, so perhaps in the future we want to change it to something else. So while I appreciate the easier debugging, I'm afraid that we'll regret adding a command-line-visible feature. I'm worried that making it explicit with a --mirror option would take away its flexibility. What about adding block_reopen and extending the blkmirror string: (qemu) block_reopen ide-hd0 \ blkmirror:qcow2:/tmp/src/hd0snap1.qcow2:/tmp/dst/hd0snap1.qcow2 so that the format is passed as first argument (and if it's empty we would use the auto-detection). No, the format of the source and destination should be independent. It would be nice to have something like this: blkmirror:src=...,dst=...,srcformat=...,dstformat=... but commas are a pain because they need escaping. Paolo
Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
- Original Message - From: Paolo Bonzini pbonz...@redhat.com To: Federico Simoncelli fsimo...@redhat.com Cc: kw...@redhat.com, mtosa...@redhat.com, qemu-devel@nongnu.org Sent: Thursday, February 23, 2012 10:48:59 AM Subject: Re: [PATCH 3/3] Add nocreate option to snapshot_blkdev On 02/23/2012 10:39 AM, Federico Simoncelli wrote: I agree on the fact that using snapshot_blkdev is a misnomer but at the same time I like very much how blkmirror is modular and it can be used as a regular image filename. True, on the other hand if we add this we will have to keep it forever. I'm worried that blkmirror does not satisfy _all_ mirroring needs, for example you cannot use block_stream to copy from the source to the destination, so perhaps in the future we want to change it to something else. Are you talking about a mirroring where you block_stream the missing clusters in the destination from the source? I believe that it could be done without losing the blkmirror modularity probably extending the BlockDriver structure with some additional concepts. So while I appreciate the easier debugging, I'm afraid that we'll regret adding a command-line-visible feature. I'm worried that making it explicit with a --mirror option would take away its flexibility. What about adding block_reopen and extending the blkmirror string: (qemu) block_reopen ide-hd0 \ blkmirror:qcow2:/tmp/src/hd0snap1.qcow2:/tmp/dst/hd0snap1.qcow2 so that the format is passed as first argument (and if it's empty we would use the auto-detection). No, the format of the source and destination should be independent. It would be nice to have something like this: blkmirror:src=...,dst=...,srcformat=...,dstformat=... but commas are a pain because they need escaping. I like that, one limitation we need to keep in mind is that it should fit into the hard-coded filename limit of 1024 characters that (sadly) we have in multiple places. Another thing is that at this stage the mirroring is more an original/copy concept rather than source/destination. What about: blkmirror:...,copy=...,fmt=... (both images uses the same fmt) blkmirror:...,copy=...,fmt=...,copyfmt=... Or, eventually if you feel like that source/destination is more appropriate for the future, then: blkmirror:...,dst=...,fmt=...,dstfmt=... -- Federico
Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
On 02/23/2012 11:19 AM, Federico Simoncelli wrote: I'm worried that blkmirror does not satisfy _all_ mirroring needs, for example you cannot use block_stream to copy from the source to the destination, so perhaps in the future we want to change it to something else. Are you talking about a mirroring where you block_stream the missing clusters in the destination from the source? I believe that it could be done without losing the blkmirror modularity probably extending the BlockDriver structure with some additional concepts. Yes, agreed. It's not the idea of a driver that I don't like; it is making it available through the command-line that worries me. This would be unlike all other filtering options (copy-on-read, I/O limits, dirty sector tracking). True, there are blkdebug and blkverify but those are for debugging only. Paolo
[Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
Signed-off-by: Federico Simoncelli fsimo...@redhat.com
---
blockdev.c | 14 --
hmp-commands.hx | 16 ++--
hmp.c|4 +++-
qapi-schema.json |8 +++-
qmp-commands.hx |2 +-
5 files changed, 29 insertions(+), 15 deletions(-)
diff --git a/blockdev.c b/blockdev.c
index 7a6613a..2c3e10a 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -647,7 +647,7 @@ void do_commit(Monitor *mon, const QDict *qdict)
void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
bool has_format, const char *format,
-Error **errp)
+bool has_nocreate, bool nocreate, Error **errp)
{
BlockDriverState *bs;
BlockDriver *drv, *old_drv, *proto_drv;
@@ -686,11 +686,13 @@ void qmp_blockdev_snapshot_sync(const char *device, const
char *snapshot_file,
return;
}
-ret = bdrv_img_create(snapshot_file, format, bs-filename,
- bs-drv-format_name, NULL, -1, flags);
-if (ret) {
-error_set(errp, QERR_UNDEFINED_ERROR);
-return;
+if (!(has_nocreate nocreate)) {
+ret = bdrv_img_create(snapshot_file, format, bs-filename,
+ bs-drv-format_name, NULL, -1, flags);
+if (ret) {
+error_set(errp, QERR_UNDEFINED_ERROR);
+return;
+}
}
bdrv_drain_all();
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 573b823..ff49412 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -868,14 +868,18 @@ ETEXI
{
.name = snapshot_blkdev,
-.args_type = device:B,snapshot-file:s?,format:s?,
-.params = device [new-image-file] [format],
+.args_type = nocreate:-n,device:B,snapshot-file:s?,format:s?,
+.params = [-n] device [new-image-file] [format],
.help = initiates a live snapshot\n\t\t\t
of device. If a new image file is specified,
the\n\t\t\t
- new image file will become the new root image.\n\t\t\t
- If format is specified, the snapshot file will\n\t\t\t
- be created in that format. Otherwise the\n\t\t\t
- snapshot will be internal! (currently unsupported),
+ new image file will be created (unless -n is\n\t\t\t
+ specified) and will become the new root image.\n\t\t\t
+ The -n (nocreate) option is potentially
dangerous\n\t\t\t
+ if the image wasn't prepared in the correct way\n\t\t\t
+ by an external manager. If format is specified,\n\t\t\t
+ the snapshot file will be created in that
format.\n\t\t\t
+ Otherwise the snapshot will be internal!\n\t\t\t
+ (currently unsupported),
.mhandler.cmd = hmp_snapshot_blkdev,
},
diff --git a/hmp.c b/hmp.c
index 8ff8c94..44868c7 100644
--- a/hmp.c
+++ b/hmp.c
@@ -684,6 +684,7 @@ void hmp_block_resize(Monitor *mon, const QDict *qdict)
void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict)
{
+int nocreate = qdict_get_try_bool(qdict, nocreate, 0);
const char *device = qdict_get_str(qdict, device);
const char *filename = qdict_get_try_str(qdict, snapshot-file);
const char *format = qdict_get_try_str(qdict, format);
@@ -697,7 +698,8 @@ void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict)
return;
}
-qmp_blockdev_snapshot_sync(device, filename, !!format, format, errp);
+qmp_blockdev_snapshot_sync(device, filename,
+ !!format, format, true, nocreate, errp);
hmp_handle_error(mon, errp);
}
diff --git a/qapi-schema.json b/qapi-schema.json
index d02ee86..ac652c2 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1116,9 +1116,14 @@
# @snapshot-file: the target of the new image. If the file exists, or if it
# is a device, the snapshot will be created in the existing
# file/device. If does not exist, a new file will be created.
+# This behavior can be overridden using the nocreate option.
#
# @format: #optional the format of the snapshot image, default is 'qcow2'.
#
+# @nocreate: #optional use the target image avoiding the creation. This is
+#a potentially dangerous option if the image wasn't prepared
+#in the correct way by an external manager.
+#
# Returns: nothing on success
# If @device is not a valid block device, DeviceNotFound
# If @snapshot-file can't be opened, OpenFileFailed
@@ -1133,7 +1138,8 @@
# Since 0.14.0
##
{ 'command': 'blockdev-snapshot-sync',
- 'data': { 'device': 'str', 'snapshot-file': 'str', '*format': 'str' } }
+ 'data': { 'device': 'str', 'snapshot-file': 'str', '*format': 'str',
+'*nocreate': 'bool' } }
##
#
Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
On 02/22/2012 06:13 PM, Federico Simoncelli wrote: Signed-off-by: Federico Simoncelli fsimo...@redhat.com What is the usecase, and how can this be tested? Paolo
Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
On 02/23/2012 08:19 AM, Paolo Bonzini wrote: Signed-off-by: Federico Simoncelli fsimo...@redhat.com What is the usecase, and how can this be tested? Oops, you explained it in part 0. Step 5 - Final Switch to Destination VM1 is now able to switch to the destination for both read and write operations. [src/hd0base] - [src/hd0snap1] = VM1(read-write) (qemu) snapshot_blkdev -n ide0-hd0 /tmp/dst/hd0snap1.qcow2 It seems to me that reusing the snapshot_blkdev command is a bit of a misnomer. It also forces you to use format autodetection for the destination in the blkmirror phase. I see two possibilities: 1) you can make a new command block_reopen; this fixes only the naming problem. 2) you can hide the new format behind a new command to be used like this: block_migrate --mirror ide-hd0 /tmp/dst/hd0snap1.qcow2 ... block_migrate --switch ide-hd0 This leave the possibility to specify the format in the future: block_migrate --mirror ide-hd0 /tmp/dst/hd0snap1.qcow2 qcow2 And we could have another sub-command block_mirror --stream ide-hd0 /tmp/dst/hd0.raw to migrate block devices without shared storage and without an intermediate snapshot. Paolo
