| Message ID | 1329930815-7995-4-git-send-email-fsimonce@redhat.com |
|---|---|
| State | New |
| Headers | show |
On 02/22/2012 06:13 PM, Federico Simoncelli wrote:
> Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
What is the usecase, and how can this be tested?
Paolo
On 02/23/2012 08:19 AM, Paolo Bonzini wrote: >> > Signed-off-by: Federico Simoncelli <fsimonce@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
----- Original Message ----- > From: "Paolo Bonzini" <pbonzini@redhat.com> > Cc: "Federico Simoncelli" <fsimonce@redhat.com>, kwolf@redhat.com, mtosatti@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 <fsimonce@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).
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
----- Original Message ----- > From: "Paolo Bonzini" <pbonzini@redhat.com> > To: "Federico Simoncelli" <fsimonce@redhat.com> > Cc: kwolf@redhat.com, mtosatti@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=...
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
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' } } ## # @human-monitor-command: diff --git a/qmp-commands.hx b/qmp-commands.hx index b5e2ab8..e717826 100644 --- a/qmp-commands.hx +++ b/qmp-commands.hx @@ -668,7 +668,7 @@ EQMP { .name = "blockdev-snapshot-sync", - .args_type = "device:B,snapshot-file:s,format:s?", + .args_type = "nocreate:-n,device:B,snapshot-file:s,format:s?", .mhandler.cmd_new = qmp_marshal_input_blockdev_snapshot_sync, },
Signed-off-by: Federico Simoncelli <fsimonce@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(-)