Re: [Qemu-devel] [PATCH V3] qemu-img create: add 'nocow' option

2014-07-01 Thread Eric Blake 
On 06/23/2014 03:17 AM, Chunyan Liu wrote:
 Add 'nocow' option so that users could have a chance to set NOCOW flag to
 newly created files. It's useful on btrfs file system to enhance performance.
 
 Btrfs has low performance when hosting VM images, even more when the guest
 in those VM are also using btrfs as file system. One way to mitigate this bad
 performance is to turn off COW attributes on VM files. Generally, there are
 two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then
 all newly created files will be NOCOW. b) per file. Add the NOCOW file
 attribute. It could only be done to empty or new files.
 
 This patch tries the second way, according to the option, it could add NOCOW
 per file.
 
 For most block drivers, since the create file step is in raw-posix.c, so we
 can do setting NOCOW flag ioctl in raw-posix.c only.
 
 But there are some exceptions, like block/vpc.c and block/vdi.c, they are
 creating file by calling qemu_open directly. For them, do the same setting
 NOCOW flag ioctl work in them separately.

Design question (not a patch review):

It looks like your patch allows one to set the NOCOW flag via ioctl when
requested.  But how does one learn if the flag is already set?  Can you
update 'qemu-img info' to show whether a file currently has the flag
set?  Can 'qemu-img amend' be taught to set and/or clear the flag on an
already existing file?


 @@ -1291,6 +1296,21 @@ static int raw_create(const char *filename, QemuOpts 
 *opts, Error **errp)
  result = -errno;
  error_setg_errno(errp, -result, Could not create file);
  } else {
 +if (nocow) {
 +#ifdef __linux__
 +/* Set NOCOW flag to solve performance issue on fs like btrfs.
 + * This is an optimisation. The FS_IOC_SETFLAGS ioctl return 
 value
 + * will be ignored since any failure of this operation should not
 + * block the left work.
 + */
 +int attr;
 +if (ioctl(fd, FS_IOC_GETFLAGS, attr) == 0) {
 +attr |= FS_NOCOW_FL;
 +ioctl(fd, FS_IOC_SETFLAGS, attr);
 +}
 +#endif
 +}

This silently ignores the nocow flag on non-Linux.  Wouldn't it be
better to reject the option as unsupported?

What happens if the ioctl fails?  Would it be better to fail the
qemu-img creation if the flag is requested but can't be honored?


 +++ b/qemu-doc.texi
 @@ -589,6 +589,22 @@ check -r all} is required, which may take some time.
  
  This option can only be enabled if @code{compat=1.1} is specified.
  
 +@item nocow
 +If this option is set to @code{on}, it will trun off COW of the file. It's 
 only

s/trun/turn/

 +valid on btrfs, no effect on other file systems.

This sort of statement may get stale, if other file systems learn to
honor the same ioctl as btrfs.

 +
 +Btrfs has low performance when hosting a VM image file, even more when the 
 guest
 +on the VM also using btrfs as file system. Turning off COW is a way to 
 mitigate
 +this bad performance. Generally there are two ways to turn off COW on btrfs:
 +a) Disable it by mounting with nodatacow, then all newly created files will 
 be
 +NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this 
 option
 +does.
 +
 +Note: this option is only valid to new or empty files. If there is an 
 existing
 +file which is COW and has data blocks already, it couldn't be changed to 
 NOCOW
 +by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
 +the NOCOW flag is set or not (Capitabl 'C' is NOCOW flag).

s/Capitabl/Capital/

Oh, so it looks like setting the attribute is one-way, and can't be
undone once something is written?  Or is it that it can only be set on
an empty file, but can be cleared at any time?

Again, making people refer to lsattr to learn if the flag is already set
seems painful; can qemu-img info be taught to expose this information,
so that one tool is sufficient to manage the entire experience?

 +++ b/qemu-img.texi
 @@ -474,6 +474,22 @@ check -r all} is required, which may take some time.
  
  This option can only be enabled if @code{compat=1.1} is specified.
  
 +@item nocow
 +If this option is set to @code{on}, it will trun off COW of the file. It's 
 only

s/trun/turn/

 +valid on btrfs, no effect on other file systems.
 +
 +Btrfs has low performance when hosting a VM image file, even more when the 
 guest
 +on the VM also using btrfs as file system. Turning off COW is a way to 
 mitigate
 +this bad performance. Generally there are two ways to turn off COW on btrfs:
 +a) Disable it by mounting with nodatacow, then all newly created files will 
 be
 +NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this 
 option
 +does.
 +
 +Note: this option is only valid to new or empty files. If there is an 
 existing
 +file which is COW and has data blocks already, it couldn't be changed to 
 NOCOW
 +by setting @code{nocow=on}. One can issue @code{lsattr

Re: [Qemu-devel] [PATCH V3] qemu-img create: add 'nocow' option

2014-07-01 Thread Chun Yan Liu 


 On 7/2/2014 at 05:02 AM, in message 53b321cc.7070...@redhat.com, Eric 
 Blake
ebl...@redhat.com wrote: 
 On 06/23/2014 03:17 AM, Chunyan Liu wrote: 
  Add 'nocow' option so that users could have a chance to set NOCOW flag to 
  newly created files. It's useful on btrfs file system to enhance  
 performance. 
   
  Btrfs has low performance when hosting VM images, even more when the guest 
  in those VM are also using btrfs as file system. One way to mitigate this  
 bad 
  performance is to turn off COW attributes on VM files. Generally, there are 
  two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then 
  all newly created files will be NOCOW. b) per file. Add the NOCOW file 
  attribute. It could only be done to empty or new files. 
   
  This patch tries the second way, according to the option, it could add  
 NOCOW 
  per file. 
   
  For most block drivers, since the create file step is in raw-posix.c, so we 
  can do setting NOCOW flag ioctl in raw-posix.c only. 
   
  But there are some exceptions, like block/vpc.c and block/vdi.c, they are 
  creating file by calling qemu_open directly. For them, do the same setting 
  NOCOW flag ioctl work in them separately. 
  
 Design question (not a patch review): 
  
 It looks like your patch allows one to set the NOCOW flag via ioctl when 
 requested.  But how does one learn if the flag is already set?  Can you 
 update 'qemu-img info' to show whether a file currently has the flag 
 set? 

The reliable way to check if the file is really NOCOW is 'lsattr filename'.
-o nocow=on not really means NOCOW successfully set. We didn't block
file creation even if ioctl fails (see below).
Maybe 'qemu-img info' can call 'lsattr filename' to judge if the file is NOCOW.

 Can 'qemu-img amend' be taught to set and/or clear the flag on an 
 already existing file? 

No. It's one way. A COW file can be not changed to NOCOW, vice versa.

  
  
  @@ -1291,6 +1296,21 @@ static int raw_create(const char *filename, QemuOpts 
   
 *opts, Error **errp) 
   result = -errno; 
   error_setg_errno(errp, -result, Could not create file); 
   } else { 
  +if (nocow) { 
  +#ifdef __linux__ 
  +/* Set NOCOW flag to solve performance issue on fs like btrfs. 
  + * This is an optimisation. The FS_IOC_SETFLAGS ioctl return  
 value 
  + * will be ignored since any failure of this operation should  
 not 
  + * block the left work. 
  + */ 
  +int attr; 
  +if (ioctl(fd, FS_IOC_GETFLAGS, attr) == 0) { 
  +attr |= FS_NOCOW_FL; 
  +ioctl(fd, FS_IOC_SETFLAGS, attr); 
  +} 
  +#endif 
  +} 
  
 This silently ignores the nocow flag on non-Linux.  Wouldn't it be 
 better to reject the option as unsupported? 

First, other file systems (at least ext3 ext4 as I checked ) not supporting that
ioctl would simply return 0.  So we couldn't rely on the ioctl return value
to check if the option is unsupported.
 
 What happens if the ioctl fails?  Would it be better to fail the 
 qemu-img creation if the flag is requested but can't be honored? 
  

NOCOW is an optimization for performance, we don't want it to block the file
creation. In other words, if ioctl fails, we still hope the file image is 
created.

Another reason for doing this is the ioctl return value is not consistent in
different file systems, ioctl return value:
0: not always means SUCCESS, could be UNSUPPORTED 
!0: could be supported but not successfuly (like in btrfs);
 could be unsupported at all but other error. (other fs. In this case, we 
don't
  want to block the file creation.)

  
  +++ b/qemu-doc.texi 
  @@ -589,6 +589,22 @@ check -r all} is required, which may take some time. 

   This option can only be enabled if @code{compat=1.1} is specified. 

  +@item nocow 
  +If this option is set to @code{on}, it will trun off COW of the file. It's 
   
 only 
  
 s/trun/turn/ 
  
  +valid on btrfs, no effect on other file systems. 
  
 This sort of statement may get stale, if other file systems learn to 
 honor the same ioctl as btrfs. 

Yes. Currently only btrfs supports this ioctl. Writting here because we didn't
check what current fs is, and we didn't have a reliable way to report the ioctl
is unsupported (as above). So to warn users in manpage.

  
  + 
  +Btrfs has low performance when hosting a VM image file, even more when the 
   
 guest 
  +on the VM also using btrfs as file system. Turning off COW is a way to  
 mitigate 
  +this bad performance. Generally there are two ways to turn off COW on  
 btrfs: 
  +a) Disable it by mounting with nodatacow, then all newly created files  
 will be 
  +NOCOW. b) For an empty file, add the NOCOW file attribute. That's what  
 this option 
  +does. 
  + 
  +Note: this option is only valid to new or empty files. If there is an  
 existing 
  +file which is COW and has data blocks already, it

Re: [Qemu-devel] [PATCH V3] qemu-img create: add 'nocow' option

2014-06-29 Thread Chun Yan Liu 


 On 6/27/2014 at 07:48 PM, in message
20140627114806.gm12...@stefanha-thinkpad.muc.redhat.com, Stefan Hajnoczi
stefa...@redhat.com wrote: 
 On Mon, Jun 23, 2014 at 05:17:02PM +0800, Chunyan Liu wrote: 
  Add 'nocow' option so that users could have a chance to set NOCOW flag to 
  newly created files. It's useful on btrfs file system to enhance  
 performance. 
   
  Btrfs has low performance when hosting VM images, even more when the guest 
  in those VM are also using btrfs as file system. One way to mitigate this  
 bad 
  performance is to turn off COW attributes on VM files. Generally, there are 
  two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then 
  all newly created files will be NOCOW. b) per file. Add the NOCOW file 
  attribute. It could only be done to empty or new files. 
   
  This patch tries the second way, according to the option, it could add  
 NOCOW 
  per file. 
   
  For most block drivers, since the create file step is in raw-posix.c, so we 
  can do setting NOCOW flag ioctl in raw-posix.c only. 
   
  But there are some exceptions, like block/vpc.c and block/vdi.c, they are 
  creating file by calling qemu_open directly. For them, do the same setting 
  NOCOW flag ioctl work in them separately. 
   
  Signed-off-by: Chunyan Liu cy...@suse.com 
  --- 
  Changes to v2: 
* based on QemuOpts instead of old QEMUOptionParameters 
* add nocow description in man page and html doc 
   
Old v2 is here: 
http://lists.gnu.org/archive/html/qemu-devel/2013-11/msg02429.html 
   
  --- 
   block/cow.c   |  5 + 
   block/qcow.c  |  5 + 
   block/qcow2.c |  5 + 
   block/qed.c   | 11 --- 
   block/raw-posix.c | 25 + 
   block/vdi.c   | 29 + 
   block/vhdx.c  |  5 + 
   block/vmdk.c  | 11 --- 
   block/vpc.c   | 29 + 
   include/block/block_int.h |  1 + 
   qemu-doc.texi | 16  
   qemu-img.texi | 16  
   12 files changed, 152 insertions(+), 6 deletions(-) 
  
 Are you sure it's necessary to touch all image formats in order to pass 
 through the nocow option?  Looking at bdrv_img_create() I think it will 
 work without touching all image formats since both drv and 
 proto_drv-create_opts are appended: 

Right. For those calling bdrv_create_file to create file, it's not necessary
to add NOCOW option to their .create_opts. Adding NOCOW to raw-posix.c
is enough. There will be no difference to users when they do:
qemu-img create -f fmt name size -o nocow=on
or
qemu-img create -f fmt name size -o ?

  
 void bdrv_img_create(const char *filename, const char *fmt, 
  const char *base_filename, const char *base_fmt, 
  char *options, uint64_t img_size, int flags, 
  Error **errp, bool quiet) 
 { 
 QemuOptsList *create_opts = NULL; 
 ... 
 create_opts = qemu_opts_append(create_opts, drv-create_opts); 
 create_opts = qemu_opts_append(create_opts, proto_drv-create_opts); 
  
 /* Create parameter list with default values */ 
 opts = qemu_opts_create(create_opts, NULL, 0, error_abort); 
 qemu_opt_set_number(opts, BLOCK_OPT_SIZE, img_size); 
  
 /* Parse -o options */ 
 if (options) { 
 if (qemu_opts_do_parse(opts, options, NULL) != 0) { 
 error_setg(errp, Invalid options for file format '%s', fmt); 
 goto out; 
 } 
 }

Re: [Qemu-devel] [PATCH V3] qemu-img create: add 'nocow' option

2014-06-27 Thread Stefan Hajnoczi 
On Mon, Jun 23, 2014 at 05:17:02PM +0800, Chunyan Liu wrote:
 Add 'nocow' option so that users could have a chance to set NOCOW flag to
 newly created files. It's useful on btrfs file system to enhance performance.
 
 Btrfs has low performance when hosting VM images, even more when the guest
 in those VM are also using btrfs as file system. One way to mitigate this bad
 performance is to turn off COW attributes on VM files. Generally, there are
 two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then
 all newly created files will be NOCOW. b) per file. Add the NOCOW file
 attribute. It could only be done to empty or new files.
 
 This patch tries the second way, according to the option, it could add NOCOW
 per file.
 
 For most block drivers, since the create file step is in raw-posix.c, so we
 can do setting NOCOW flag ioctl in raw-posix.c only.
 
 But there are some exceptions, like block/vpc.c and block/vdi.c, they are
 creating file by calling qemu_open directly. For them, do the same setting
 NOCOW flag ioctl work in them separately.
 
 Signed-off-by: Chunyan Liu cy...@suse.com
 ---
 Changes to v2:
   * based on QemuOpts instead of old QEMUOptionParameters
   * add nocow description in man page and html doc
 
   Old v2 is here:
   http://lists.gnu.org/archive/html/qemu-devel/2013-11/msg02429.html
 
 ---
  block/cow.c   |  5 +
  block/qcow.c  |  5 +
  block/qcow2.c |  5 +
  block/qed.c   | 11 ---
  block/raw-posix.c | 25 +
  block/vdi.c   | 29 +
  block/vhdx.c  |  5 +
  block/vmdk.c  | 11 ---
  block/vpc.c   | 29 +
  include/block/block_int.h |  1 +
  qemu-doc.texi | 16 
  qemu-img.texi | 16 
  12 files changed, 152 insertions(+), 6 deletions(-)

Are you sure it's necessary to touch all image formats in order to pass
through the nocow option?  Looking at bdrv_img_create() I think it will
work without touching all image formats since both drv and
proto_drv-create_opts are appended:

void bdrv_img_create(const char *filename, const char *fmt,
 const char *base_filename, const char *base_fmt,
 char *options, uint64_t img_size, int flags,
 Error **errp, bool quiet)
{
QemuOptsList *create_opts = NULL;
...
create_opts = qemu_opts_append(create_opts, drv-create_opts);
create_opts = qemu_opts_append(create_opts, proto_drv-create_opts);

/* Create parameter list with default values */
opts = qemu_opts_create(create_opts, NULL, 0, error_abort);
qemu_opt_set_number(opts, BLOCK_OPT_SIZE, img_size);

/* Parse -o options */
if (options) {
if (qemu_opts_do_parse(opts, options, NULL) != 0) {
error_setg(errp, Invalid options for file format '%s', fmt);
goto out;
}
}


pgpn82sRWQr9t.pgp
Description: PGP signature

Re: [Qemu-devel] [PATCH V3] qemu-img create: add 'nocow' option

2014-06-26 Thread Chun Yan Liu 
Hi, Stefan  Kevin,

Could you help to have a look at this version? We've discussed about
this last November and now switch it to QemuOpts.

Thanks,
Chunyan

 On 6/23/2014 at 05:17 PM, in message
1403515022-24802-1-git-send-email-cy...@suse.com, Chunyan Liu
cy...@suse.com wrote: 
 Add 'nocow' option so that users could have a chance to set NOCOW flag to 
 newly created files. It's useful on btrfs file system to enhance  
 performance. 
  
 Btrfs has low performance when hosting VM images, even more when the guest 
 in those VM are also using btrfs as file system. One way to mitigate this  
 bad 
 performance is to turn off COW attributes on VM files. Generally, there are 
 two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then 
 all newly created files will be NOCOW. b) per file. Add the NOCOW file 
 attribute. It could only be done to empty or new files. 
  
 This patch tries the second way, according to the option, it could add NOCOW 
 per file. 
  
 For most block drivers, since the create file step is in raw-posix.c, so we 
 can do setting NOCOW flag ioctl in raw-posix.c only. 
  
 But there are some exceptions, like block/vpc.c and block/vdi.c, they are 
 creating file by calling qemu_open directly. For them, do the same setting 
 NOCOW flag ioctl work in them separately. 
  
 Signed-off-by: Chunyan Liu cy...@suse.com 
 --- 
 Changes to v2: 
   * based on QemuOpts instead of old QEMUOptionParameters 
   * add nocow description in man page and html doc 
  
   Old v2 is here: 
   http://lists.gnu.org/archive/html/qemu-devel/2013-11/msg02429.html 
  
 --- 
  block/cow.c   |  5 + 
  block/qcow.c  |  5 + 
  block/qcow2.c |  5 + 
  block/qed.c   | 11 --- 
  block/raw-posix.c | 25 + 
  block/vdi.c   | 29 + 
  block/vhdx.c  |  5 + 
  block/vmdk.c  | 11 --- 
  block/vpc.c   | 29 + 
  include/block/block_int.h |  1 + 
  qemu-doc.texi | 16  
  qemu-img.texi | 16  
  12 files changed, 152 insertions(+), 6 deletions(-) 
  
 diff --git a/block/cow.c b/block/cow.c 
 index a05a92c..43b537c 100644 
 --- a/block/cow.c 
 +++ b/block/cow.c 
 @@ -401,6 +401,11 @@ static QemuOptsList cow_create_opts = { 
  .type = QEMU_OPT_STRING, 
  .help = File name of a base image 
  }, 
 +{ 
 +.name = BLOCK_OPT_NOCOW, 
 +.type = QEMU_OPT_BOOL, 
 +.help = Turn off copy-on-write (valid only on btrfs) 
 +}, 
  { /* end of list */ } 
  } 
  }; 
 diff --git a/block/qcow.c b/block/qcow.c 
 index 1f2bac8..5b23540 100644 
 --- a/block/qcow.c 
 +++ b/block/qcow.c 
 @@ -928,6 +928,11 @@ static QemuOptsList qcow_create_opts = { 
  .help = Encrypt the image, 
  .def_value_str = off 
  }, 
 +{ 
 +.name = BLOCK_OPT_NOCOW, 
 +.type = QEMU_OPT_BOOL, 
 +.help = Turn off copy-on-write (valid only on btrfs) 
 +}, 
  { /* end of list */ } 
  } 
  }; 
 diff --git a/block/qcow2.c b/block/qcow2.c 
 index b9d2fa6..3a4cc8a 100644 
 --- a/block/qcow2.c 
 +++ b/block/qcow2.c 
 @@ -2382,6 +2382,11 @@ static QemuOptsList qcow2_create_opts = { 
  .help = Postpone refcount updates, 
  .def_value_str = off 
  }, 
 +{ 
 +.name = BLOCK_OPT_NOCOW, 
 +.type = QEMU_OPT_BOOL, 
 +.help = Turn off copy-on-write (valid only on btrfs) 
 +}, 
  { /* end of list */ } 
  } 
  }; 
 diff --git a/block/qed.c b/block/qed.c 
 index 092e6fb..460ac92 100644 
 --- a/block/qed.c 
 +++ b/block/qed.c 
 @@ -567,7 +567,7 @@ static void bdrv_qed_close(BlockDriverState *bs) 
  static int qed_create(const char *filename, uint32_t cluster_size, 
uint64_t image_size, uint32_t table_size, 
const char *backing_file, const char *backing_fmt, 
 -  Error **errp) 
 +  QemuOpts *opts, Error **errp) 
  { 
  QEDHeader header = { 
  .magic = QED_MAGIC, 
 @@ -586,7 +586,7 @@ static int qed_create(const char *filename, uint32_t  
 cluster_size, 
  int ret = 0; 
  BlockDriverState *bs; 
   
 -ret = bdrv_create_file(filename, NULL, local_err); 
 +ret = bdrv_create_file(filename, opts, local_err); 
  if (ret  0) { 
  error_propagate(errp, local_err); 
  return ret; 
 @@ -682,7 +682,7 @@ static int bdrv_qed_create(const char *filename, QemuOpts 
  
 *opts, Error **errp) 
  } 
   
  ret = qed_create(filename, cluster_size, image_size, table_size, 
 - backing_file, backing_fmt, errp); 
 + backing_file, backing_fmt, opts, errp); 
   
  finish:

[Qemu-devel] [PATCH V3] qemu-img create: add 'nocow' option

2014-06-23 Thread Chunyan Liu 
Add 'nocow' option so that users could have a chance to set NOCOW flag to
newly created files. It's useful on btrfs file system to enhance performance.

Btrfs has low performance when hosting VM images, even more when the guest
in those VM are also using btrfs as file system. One way to mitigate this bad
performance is to turn off COW attributes on VM files. Generally, there are
two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then
all newly created files will be NOCOW. b) per file. Add the NOCOW file
attribute. It could only be done to empty or new files.

This patch tries the second way, according to the option, it could add NOCOW
per file.

For most block drivers, since the create file step is in raw-posix.c, so we
can do setting NOCOW flag ioctl in raw-posix.c only.

But there are some exceptions, like block/vpc.c and block/vdi.c, they are
creating file by calling qemu_open directly. For them, do the same setting
NOCOW flag ioctl work in them separately.

Signed-off-by: Chunyan Liu cy...@suse.com
---
Changes to v2:
  * based on QemuOpts instead of old QEMUOptionParameters
  * add nocow description in man page and html doc

  Old v2 is here:
  http://lists.gnu.org/archive/html/qemu-devel/2013-11/msg02429.html

---
 block/cow.c   |  5 +
 block/qcow.c  |  5 +
 block/qcow2.c |  5 +
 block/qed.c   | 11 ---
 block/raw-posix.c | 25 +
 block/vdi.c   | 29 +
 block/vhdx.c  |  5 +
 block/vmdk.c  | 11 ---
 block/vpc.c   | 29 +
 include/block/block_int.h |  1 +
 qemu-doc.texi | 16 
 qemu-img.texi | 16 
 12 files changed, 152 insertions(+), 6 deletions(-)

diff --git a/block/cow.c b/block/cow.c
index a05a92c..43b537c 100644
--- a/block/cow.c
+++ b/block/cow.c
@@ -401,6 +401,11 @@ static QemuOptsList cow_create_opts = {
 .type = QEMU_OPT_STRING,
 .help = File name of a base image
 },
+{
+.name = BLOCK_OPT_NOCOW,
+.type = QEMU_OPT_BOOL,
+.help = Turn off copy-on-write (valid only on btrfs)
+},
 { /* end of list */ }
 }
 };
diff --git a/block/qcow.c b/block/qcow.c
index 1f2bac8..5b23540 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -928,6 +928,11 @@ static QemuOptsList qcow_create_opts = {
 .help = Encrypt the image,
 .def_value_str = off
 },
+{
+.name = BLOCK_OPT_NOCOW,
+.type = QEMU_OPT_BOOL,
+.help = Turn off copy-on-write (valid only on btrfs)
+},
 { /* end of list */ }
 }
 };
diff --git a/block/qcow2.c b/block/qcow2.c
index b9d2fa6..3a4cc8a 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2382,6 +2382,11 @@ static QemuOptsList qcow2_create_opts = {
 .help = Postpone refcount updates,
 .def_value_str = off
 },
+{
+.name = BLOCK_OPT_NOCOW,
+.type = QEMU_OPT_BOOL,
+.help = Turn off copy-on-write (valid only on btrfs)
+},
 { /* end of list */ }
 }
 };
diff --git a/block/qed.c b/block/qed.c
index 092e6fb..460ac92 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -567,7 +567,7 @@ static void bdrv_qed_close(BlockDriverState *bs)
 static int qed_create(const char *filename, uint32_t cluster_size,
   uint64_t image_size, uint32_t table_size,
   const char *backing_file, const char *backing_fmt,
-  Error **errp)
+  QemuOpts *opts, Error **errp)
 {
 QEDHeader header = {
 .magic = QED_MAGIC,
@@ -586,7 +586,7 @@ static int qed_create(const char *filename, uint32_t 
cluster_size,
 int ret = 0;
 BlockDriverState *bs;
 
-ret = bdrv_create_file(filename, NULL, local_err);
+ret = bdrv_create_file(filename, opts, local_err);
 if (ret  0) {
 error_propagate(errp, local_err);
 return ret;
@@ -682,7 +682,7 @@ static int bdrv_qed_create(const char *filename, QemuOpts 
*opts, Error **errp)
 }
 
 ret = qed_create(filename, cluster_size, image_size, table_size,
- backing_file, backing_fmt, errp);
+ backing_file, backing_fmt, opts, errp);
 
 finish:
 g_free(backing_file);
@@ -1644,6 +1644,11 @@ static QemuOptsList qed_create_opts = {
 .type = QEMU_OPT_SIZE,
 .help = L1/L2 table size (in clusters)
 },
+{
+.name = BLOCK_OPT_NOCOW,
+.type = QEMU_OPT_BOOL,
+.help = Turn off copy-on-write (valid only on btrfs)
+},
 { /* end of list */ }
 }
 };
diff --git a/block/raw-posix.c b/block/raw-posix.c
index dacf4fb..825a0c8 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -55,6 +55,9 @@
 #include