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

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

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.

-- 
Regards,
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}).
>>   ETEXI
>>
>>   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:
>>   @example
>>   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:
>>   @example
>>   qemu-system-i386 -drive if=ide,index=1,media=cdrom
>>   @end example
>> --
>> 1.7.11.4
>>
>>
>