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Re: [libvirt] [Qemu-devel] [PATCH 3/4] qemu-config: Add -drive fd and opaque options

On 10/05/2012 02:25 PM, Blue Swirl wrote:
On Fri, Oct 5, 2012 at 6:07 PM, Corey Bryant <coreyb linux vnet ibm com> wrote:
These new options can be used for passing drive file descriptors
on the command line, instead of using the file option to specify
a file name.

These new command line options mirror the existing add-fd QMP
command which allows an fd to be passed to QEMU via SCM_RIGHTS and
added to an fd set.  The opaque option is also available with
add-fd, and allows a free-form string to be stored in the fd set
along with the fd.

Signed-off-by: Corey Bryant <coreyb linux vnet ibm com>
  qemu-config.c   |  8 ++++++++
  qemu-options.hx | 15 +++++++++++++--
  2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/qemu-config.c b/qemu-config.c
index cd1ec21..91053dd 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -114,6 +114,14 @@ static QemuOptsList qemu_drive_opts = {
              .name = "copy-on-read",
              .type = QEMU_OPT_BOOL,
              .help = "copy read data from backing file into image file",
+        },{
+            .name = "fd",
+            .type = QEMU_OPT_NUMBER,
+            .help = "disk image file descriptor",
+        },{
+            .name = "opaque",

'opaque' is not very descriptive and it's also not obvious (except
from the help text) that it's only interesting for file descriptors.
How about fd_name, fd_tag or fd_descr?

I'd like to mirror the add-fd QMP command as much as possible:

{ 'command': 'add-fd', 'data': {'*fdset-id': 'int', '*opaque': 'str'},
  'returns': 'AddfdInfo' }

And I think use of opaque will make more sense if I don't merge these options in to -drive, and instead create a new command specifically for adding fds, like Eric is suggesting.

Corey Bryant

+            .type = QEMU_OPT_STRING,
+            .help = "free-form string used to describe fd",
          { /* end of list */ }
diff --git a/qemu-options.hx b/qemu-options.hx
index 7d97f96..513530f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -149,7 +149,7 @@ using @file{/dev/cdrom} as filename (@pxref{host_drives}).

  DEF("drive", HAS_ARG, QEMU_OPTION_drive,
-    "-drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n"
+    "-drive [file=file|fd=fd[,opaque=o]][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n"
      "       [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n"
      "       [,cache=writethrough|writeback|none|directsync|unsafe][,format=f]\n"
      "       [,serial=s][,addr=A][,id=name][,aio=threads|native]\n"
@@ -170,6 +170,12 @@ this drive. If the filename contains comma, you must double it

  Special files such as iSCSI devices can be specified using protocol
  specific URLs. See the section for "Device URL Syntax" for more information.
+ item fd= var{fd}
+This option defines which disk image (@pxref{disk_images}) file descriptor to
+use with this drive.
+ item opaque= var{opaque}
+This option defines a free-form string that describes @var{fd}.  This is used
+when storing @var{fd} in a file descriptor set.
  @item if= var{interface}
  This option defines on which type on interface the drive is connected.
  Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio.
@@ -257,12 +263,17 @@ qemu-system-i386 -drive file=file,index=2,media=disk
  qemu-system-i386 -drive file=file,index=3,media=disk
  @end example

+You can open an image using a pre-opened file descriptor:
+ example
+qemu-system-i386 -drive fd=24,opaque="rdwr:/path/to/file",index=0,media=disk
+ end example
  You can connect a CDROM to the slave of ide0:
  qemu-system-i386 -drive file=file,if=ide,index=1,media=cdrom
  @end example

-If you don't specify the "file=" argument, you define an empty drive:
+If you don't specify the "file=" or "fd=" arguments, you define an empty drive:
  qemu-system-i386 -drive if=ide,index=1,media=cdrom
  @end example

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