[Qemu-devel] QEMU online guest disk resize wrt host block devices

[Qemu-devel] QEMU online guest disk resize wrt host block devices

[Daniel P. Berrange]

We want to support online resize of guest disks in the libvirt API for
QEMU, and had intended to use the fairly recently added 'block_resize'
command:

  commit db97ee6a976bacbb0d18818e951cfc41b39269a7
  Author: Christoph Hellwig <hch@lst.de>
  Date:   Mon Jan 24 13:32:41 2011 +0100
 
    block: tell drivers about an image resize

  commit 6d4a2b3a47959f02e7f307f50396e70e8464f95e
  Author: Christoph Hellwig <hch@lst.de>
  Date:   Mon Jan 24 13:32:33 2011 +0100

    block: add block_resize monitor command

There is unfortunately a problem with the design of this monitor command
because it has tied the task of resizing the host backing file for the
virtual disk, together with the task of notifying the guest device of the
block resize. This means that we can only use 'block_resize' for disks
that are backed by image files (raw, qcow2, etc) that QEMU can actually
resize.

To be able to support online resize of virtual disks backed by host
block devices, LVM volumes, SCSI LUNs, iSCSI LUNs, etc we need to be
able to decouple these tasks. The resize of the block device needs to
be done outside QEMU, either by privileged tools on the host, or by a
remote SAN administrator, or a combo of both.

IOW, we need a way to tell QEMU to merely re-read the host file/block
size to detect an externally performed resize, and then just notify
the guest. While this would also be sufficient for raw file images,
obviously we don't want todo this with any of the magic formats where
QEMU has to remain in charge of updating metadata while active.

I see two likely approaches:

 1. Add a parameter to the existing 'block_resize' command
    'refreshonly=true|false'

 2. Add a separate command  'block_refresh'

Both of these options would internally just re-read the capacity of the
BlockDriver image, and then notify the guest device.

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|

Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Christoph Hellwig]

On Thu, Sep 01, 2011 at 02:27:55PM +0100, Daniel P. Berrange wrote:
> I see two likely approaches:
> 
>  1. Add a parameter to the existing 'block_resize' command
>     'refreshonly=true|false'
> 
>  2. Add a separate command  'block_refresh'

I think all that you need is a to implement a bdrv_truncate method
for host devices that simply checks if the new size smaller or equal
to the device size, and return 0 in that case or an error otherwise.

Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Daniel P. Berrange]

On Thu, Sep 01, 2011 at 02:27:55PM +0100, Daniel P. Berrange wrote:
> We want to support online resize of guest disks in the libvirt API for
> QEMU, and had intended to use the fairly recently added 'block_resize'
> command:
> 
>   commit db97ee6a976bacbb0d18818e951cfc41b39269a7
>   Author: Christoph Hellwig <hch@lst.de>
>   Date:   Mon Jan 24 13:32:41 2011 +0100
>  
>     block: tell drivers about an image resize
> 
>   commit 6d4a2b3a47959f02e7f307f50396e70e8464f95e
>   Author: Christoph Hellwig <hch@lst.de>
>   Date:   Mon Jan 24 13:32:33 2011 +0100
> 
>     block: add block_resize monitor command
> 
> There is unfortunately a problem with the design of this monitor command
> because it has tied the task of resizing the host backing file for the
> virtual disk, together with the task of notifying the guest device of the
> block resize. This means that we can only use 'block_resize' for disks
> that are backed by image files (raw, qcow2, etc) that QEMU can actually
> resize.

One other question too, when creating a qcow2 image via 'qemu-img create'
you can specify a 'prealloc' option to require metadata to be allocated
at time of creation.

Should we have the same control at time of resize too. If the app had
originally created the qcow2 image with preallocated metadata, then
I'd expect they want to pre-allocate metadata when extending it too,
or is there no additional metadata allocation required when extending
an image ?


Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|

Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Daniel P. Berrange]

On Thu, Sep 01, 2011 at 04:05:26PM +0200, Christoph Hellwig wrote:
> On Thu, Sep 01, 2011 at 02:27:55PM +0100, Daniel P. Berrange wrote:
> > I see two likely approaches:
> > 
> >  1. Add a parameter to the existing 'block_resize' command
> >     'refreshonly=true|false'
> > 
> >  2. Add a separate command  'block_refresh'
> 
> I think all that you need is a to implement a bdrv_truncate method
> for host devices that simply checks if the new size smaller or equal
> to the device size, and return 0 in that case or an error otherwise.

Hmm, yes that is another option. I'll see if I can cook up a patch
for doing that.

Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|

Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Christoph Hellwig]

Please try the attached (untested) patch:


Index: qemu/block/raw-posix.c
===================================================================
--- qemu.orig/block/raw-posix.c	2011-09-01 17:37:42.579651525 +0200
+++ qemu/block/raw-posix.c	2011-09-01 17:43:28.882967337 +0200
@@ -645,10 +645,23 @@ static void raw_close(BlockDriverState *
 static int raw_truncate(BlockDriverState *bs, int64_t offset)
 {
     BDRVRawState *s = bs->opaque;
-    if (s->type != FTYPE_FILE)
-        return -ENOTSUP;
-    if (ftruncate(s->fd, offset) < 0)
+    struct stat st;
+
+    if (fstat(s->fd, &st))
         return -errno;
+
+    if (S_ISREG(st.st_mode)) {
+        if (ftruncate(s->fd, offset) < 0)
+            return -errno;
+    } else if (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode)) {
+       if (offset > raw_getlength(bs)) {
+           return -EINVAL;
+       }
+       return 0;
+
+    } else {
+        return -ENOTSUP;
+    }
     return 0;
 }
 
@@ -1167,6 +1180,7 @@ static BlockDriver bdrv_host_device = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate = raw_truncate,
     .bdrv_getlength	= raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,
@@ -1288,6 +1302,7 @@ static BlockDriver bdrv_host_floppy = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate = raw_truncate,
     .bdrv_getlength	= raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,
@@ -1389,6 +1404,7 @@ static BlockDriver bdrv_host_cdrom = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate = raw_truncate,
     .bdrv_getlength     = raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,
@@ -1510,6 +1526,7 @@ static BlockDriver bdrv_host_cdrom = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate = raw_truncate,
     .bdrv_getlength     = raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,

Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Christoph Hellwig]

On Thu, Sep 01, 2011 at 03:27:35PM +0100, Daniel P. Berrange wrote:
> One other question too, when creating a qcow2 image via 'qemu-img create'
> you can specify a 'prealloc' option to require metadata to be allocated
> at time of creation.
> 
> Should we have the same control at time of resize too. If the app had
> originally created the qcow2 image with preallocated metadata, then
> I'd expect they want to pre-allocate metadata when extending it too,
> or is there no additional metadata allocation required when extending
> an image ?

Sounds reasonable.  Keving, is there a sane way to implement this?

> 
> 
> Daniel
> -- 
> |: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
> |: http://libvirt.org              -o-             http://virt-manager.org :|
> |: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
> |: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|
---end quoted text---

Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Daniel P. Berrange]

On Thu, Sep 01, 2011 at 05:55:43PM +0200, Christoph Hellwig wrote:
> Please try the attached (untested) patch:

Yes, this patch worked succesfully with the following test case:

  $ dd if=/dev/zero of=loop.img bs=1M seek=100 count=0
  $ losetup -f loop.img

  $ ./x86_64-softmmu/qemu-system-x86_64 -hda /dev/loop0 -monitor stdio
  (qemu) info block
  ide0-hd0: removable=0 file=/dev/loop0 sectors=204800 ro=0 drv=raw encrypted=0
  ide1-cd0: removable=1 locked=0 [not inserted]
  floppy0: removable=1 locked=0 [not inserted]
  sd0: removable=1 locked=0 [not inserted]


  $ dd if=/dev/zero of=loop.img bs=1M seek=200 count=0
  $ losetup -c /dev/loop0 


  (qemu) block_resize ide0-hd0 200
  (qemu) info block
  ide0-hd0: removable=0 file=/dev/loop0 sectors=409600 ro=0 drv=raw encrypted=0
  ide1-cd0: removable=1 locked=0 [not inserted]
  floppy0: removable=1 locked=0 [not inserted]
  sd0: removable=1 locked=0 [not inserted]

Regards,
Daniel

> Index: qemu/block/raw-posix.c
> ===================================================================
> --- qemu.orig/block/raw-posix.c	2011-09-01 17:37:42.579651525 +0200
> +++ qemu/block/raw-posix.c	2011-09-01 17:43:28.882967337 +0200
> @@ -645,10 +645,23 @@ static void raw_close(BlockDriverState *
>  static int raw_truncate(BlockDriverState *bs, int64_t offset)
>  {
>      BDRVRawState *s = bs->opaque;
> -    if (s->type != FTYPE_FILE)
> -        return -ENOTSUP;
> -    if (ftruncate(s->fd, offset) < 0)
> +    struct stat st;
> +
> +    if (fstat(s->fd, &st))
>          return -errno;
> +
> +    if (S_ISREG(st.st_mode)) {
> +        if (ftruncate(s->fd, offset) < 0)
> +            return -errno;
> +    } else if (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode)) {
> +       if (offset > raw_getlength(bs)) {
> +           return -EINVAL;
> +       }
> +       return 0;
> +
> +    } else {
> +        return -ENOTSUP;
> +    }
>      return 0;
>  }
>  
> @@ -1167,6 +1180,7 @@ static BlockDriver bdrv_host_device = {
>  
>      .bdrv_read          = raw_read,
>      .bdrv_write         = raw_write,
> +    .bdrv_truncate = raw_truncate,
>      .bdrv_getlength	= raw_getlength,
>      .bdrv_get_allocated_file_size
>                          = raw_get_allocated_file_size,
> @@ -1288,6 +1302,7 @@ static BlockDriver bdrv_host_floppy = {
>  
>      .bdrv_read          = raw_read,
>      .bdrv_write         = raw_write,
> +    .bdrv_truncate = raw_truncate,
>      .bdrv_getlength	= raw_getlength,
>      .bdrv_get_allocated_file_size
>                          = raw_get_allocated_file_size,
> @@ -1389,6 +1404,7 @@ static BlockDriver bdrv_host_cdrom = {
>  
>      .bdrv_read          = raw_read,
>      .bdrv_write         = raw_write,
> +    .bdrv_truncate = raw_truncate,
>      .bdrv_getlength     = raw_getlength,
>      .bdrv_get_allocated_file_size
>                          = raw_get_allocated_file_size,
> @@ -1510,6 +1526,7 @@ static BlockDriver bdrv_host_cdrom = {
>  
>      .bdrv_read          = raw_read,
>      .bdrv_write         = raw_write,
> +    .bdrv_truncate = raw_truncate,
>      .bdrv_getlength     = raw_getlength,
>      .bdrv_get_allocated_file_size
>                          = raw_get_allocated_file_size,

Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Kevin Wolf]

Am 01.09.2011 17:56, schrieb Christoph Hellwig:
> On Thu, Sep 01, 2011 at 03:27:35PM +0100, Daniel P. Berrange wrote:
>> One other question too, when creating a qcow2 image via 'qemu-img create'
>> you can specify a 'prealloc' option to require metadata to be allocated
>> at time of creation.
>>
>> Should we have the same control at time of resize too. If the app had
>> originally created the qcow2 image with preallocated metadata, then
>> I'd expect they want to pre-allocate metadata when extending it too,
>> or is there no additional metadata allocation required when extending
>> an image ?
> 
> Sounds reasonable.  Keving, is there a sane way to implement this?

Implementing the functionality itself shouldn't be a big problem. The
big question is what the right interface would look like.

We have driver specific preallocation options, so we would end up with
something like this: bdrv_truncate(bs, int64_t size, char*
prealloc_mode). Not exactly nice. And is preallocation the only thing or
would we need to pass a whole option list like for image creation?

Of course, if this is a real requirement and not only a random thought,
we can always introduce a specific flag for the current use case and add
the generic thing only later when we have thought a bit more about it.

Kevin

[Qemu-devel] [PATCH] block: allow resizing of images residing on host devices

[Christoph Hellwig]

Allow to resize images that reside on host devices up to the available
space.  This allows to grow images after resizing the device manually or
vice versa.

Reviewed-by: Christoph Hellwig <hch@lst.de>

Index: qemu/block/raw-posix.c
===================================================================
--- qemu.orig/block/raw-posix.c	2011-09-01 17:37:42.579651525 +0200
+++ qemu/block/raw-posix.c	2011-09-01 17:43:28.882967337 +0200
@@ -645,10 +645,23 @@ static void raw_close(BlockDriverState *
 static int raw_truncate(BlockDriverState *bs, int64_t offset)
 {
     BDRVRawState *s = bs->opaque;
-    if (s->type != FTYPE_FILE)
-        return -ENOTSUP;
-    if (ftruncate(s->fd, offset) < 0)
+    struct stat st;
+
+    if (fstat(s->fd, &st))
         return -errno;
+
+    if (S_ISREG(st.st_mode)) {
+        if (ftruncate(s->fd, offset) < 0)
+            return -errno;
+    } else if (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode)) {
+       if (offset > raw_getlength(bs)) {
+           return -EINVAL;
+       }
+       return 0;
+
+    } else {
+        return -ENOTSUP;
+    }
     return 0;
 }
 
@@ -1167,6 +1180,7 @@ static BlockDriver bdrv_host_device = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate      = raw_truncate,
     .bdrv_getlength	= raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,
@@ -1288,6 +1302,7 @@ static BlockDriver bdrv_host_floppy = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate      = raw_truncate,
     .bdrv_getlength	= raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,
@@ -1389,6 +1404,7 @@ static BlockDriver bdrv_host_cdrom = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate      = raw_truncate,
     .bdrv_getlength     = raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,
@@ -1510,6 +1526,7 @@ static BlockDriver bdrv_host_cdrom = {
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
+    .bdrv_truncate      = raw_truncate,
     .bdrv_getlength     = raw_getlength,
     .bdrv_get_allocated_file_size
                         = raw_get_allocated_file_size,

Re: [Qemu-devel] [PATCH] block: allow resizing of images residing on host devices

[Kevin Wolf]

Am 07.09.2011 13:02, schrieb Christoph Hellwig:
> Allow to resize images that reside on host devices up to the available
> space.  This allows to grow images after resizing the device manually or
> vice versa.
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

You mean Signed-off-by, no?

> Index: qemu/block/raw-posix.c
> ===================================================================
> --- qemu.orig/block/raw-posix.c	2011-09-01 17:37:42.579651525 +0200
> +++ qemu/block/raw-posix.c	2011-09-01 17:43:28.882967337 +0200
> @@ -645,10 +645,23 @@ static void raw_close(BlockDriverState *
>  static int raw_truncate(BlockDriverState *bs, int64_t offset)
>  {
>      BDRVRawState *s = bs->opaque;
> -    if (s->type != FTYPE_FILE)
> -        return -ENOTSUP;
> -    if (ftruncate(s->fd, offset) < 0)
> +    struct stat st;
> +
> +    if (fstat(s->fd, &st))
>          return -errno;

Coding style requires braces.

> +
> +    if (S_ISREG(st.st_mode)) {
> +        if (ftruncate(s->fd, offset) < 0)
> +            return -errno;

Here as well.

> +    } else if (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode)) {
> +       if (offset > raw_getlength(bs)) {
> +           return -EINVAL;
> +       }
> +       return 0;

This return isn't needed and it's not there in the S_ISREG case. It
should be symmetrical at least.

Semantically the patch looks okay.

Kevin