Xen users - Mar 2009 - "xm dmesg" ring buffer size option?

I have a large system with pretty voluminous boot time messages that
are exceeding the capacity of the ring buffer displayed by "xm dmesg"
(i.e., the early messages are lost, and I see only the last messages).
With a regular, non-Xen kernel, I use "log_buf_len=size" to enlarge
the
printk ring buffer size, but this boot option doesn''t seem to work
for Xen.

Anyone have a handy tip for this problem?  Thanks in advance.

P.S.  I also don''t have access to the serial port, so cannot capture
the desired output via that method either.

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>From: James Takahashi
>Sent: Wednesday, March 25, 2009 12:50 PM
>To: xen-users@lists.xensource.com
>Subject: [Xen-users] "xm dmesg" ring buffer size option?
>
>I have a large system with pretty voluminous boot time messages that
>are exceeding the capacity of the ring buffer displayed by "xm
dmesg"
>(i.e., the early messages are lost, and I see only the last messages).
>With a regular, non-Xen kernel, I use "log_buf_len=size" to
enlarge the
>printk ring buffer size, but this boot option doesn''t seem to work
>for Xen.
>
>Anyone have a handy tip for this problem?  Thanks in advance.
>
>P.S.  I also don''t have access to the serial port, so cannot
capture
>the desired output via that method either.
It looks that two hard sizes limit xm dmesg outputs, which don''t allow
for change for now but you may change it manually:

tools/python/xen/lowlevel/xc/xc.c:
pyxc_readconsolering:
	char         _str[32768], *str = _str;
	unsigned int count = 32768;
Here the query buffer is limited to 32k

xen/drivers/char/console.c
#define CONRING_SIZE 16384
#define CONRING_IDX_MASK(i) ((i)&(CONRING_SIZE-1))
static char conring[CONRING_SIZE];

Above limits Xen to only log 16k outputs

Thanks,
Kevin
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