Re: [Qemu-devel] [PATCH v2 1/2] Generalize -machine command line option

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-05-24 18:06, Ian Campbell wrote:
> On Sun, 2011-05-22 at 13:00 +0200, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> -machine somehow suggests that it selects the machine, but it doesn't.
>> Fix that before this command is set in stone.
>>
>> Actually, -machine should supersede -M and allow to introduce arbitrary
>> per-machine options to the command line. That will change the internal
>> realization again, but we will be able to keep the user interface
>> stable.
>>
>> CC: Anthony PERARD <anthony.perard@citrix.com>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> 
> "-machine xenfv" doesn't work for me with this patch, it gives:
>         Program received signal SIGSEGV, Segmentation fault.
>         hypercall_buffer_cache_lock (xch=0x0) at xc_hcall_buf.c:36
>         36	xc_hcall_buf.c: No such file or directory.
>         	in xc_hcall_buf.c
>         (gdb) bt
>         #0  hypercall_buffer_cache_lock (xch=0x0) at xc_hcall_buf.c:36
>         #1  0xb7d53f1d in hypercall_buffer_cache_alloc (xch=0x0, b=0xbffff77c, nr_pages=1) at xc_hcall_buf.c:52
>         #2  xc__hypercall_buffer_alloc_pages (xch=0x0, b=0xbffff77c, nr_pages=1) at xc_hcall_buf.c:128
>         #3  0xb7d54028 in xc__hypercall_buffer_alloc (xch=0x0, b=0xbffff77c, size=16) at xc_hcall_buf.c:162
>         #4  0xb7d42719 in xc_get_hvm_param (handle=0x0, dom=248, param=5, value=0xbffff810) at xc_domain.c:1078
>         #5  0x08252777 in xen_hvm_init () at /home/ianc/devel/qemu.git/xen-all.c:803
>         #6  0x082921e9 in pc_xen_hvm_init (ram_size=536870912, boot_device=0xbffffabb "cda", kernel_filename=0x0, kernel_cmdline=0x82d648f "", initrd_filename=0x0, cpu_model=0x0) at /home/ianc/devel/qemu.git/hw/pc_piix.c:246
>         #7  0x081e3f0e in main (argc=26, argv=0xbffffba4, envp=0xbffffc10) at /home/ianc/devel/qemu.git/vl.c:3162
> 
> I suspect this is because xen_init() (which sets xch) is never called,
> perhaps because it causes the accelerator to always be tcg? If I use
> "-machine xenfv,accel=xen" then it works as expected, -M continues to
> work too AFAICT.
> 
> It would be nice to retain the behaviour of defaulting to accel=xen for
> machine=xenfv. (to be honest I can't quite see where this behaviour came
> from, nor what about this patch changes it...)

Well, first of all I think this revealed a Xen bug because it crashes
when you try to run xenfv with an inappropriate accelerator, no? What is
the result of -machine xenfv,accel=tcg or, without my patch, -M xenfv
-machine accel=tcg?

Then the question is what accel options are actually picked with
-machine xenfv, or why the default options are maybe not considered. I
don't have any Xen around, but I will check how far I can debug this -
or actually try to understand what I coded if nothing helps.

Thanks for testing!
Jan

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