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Re: [Xen-devel] [PATCH] 14287 followup - console

To: Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] 14287 followup - console
From: Ben Thomas <bthomas@xxxxxxxxxxxxxxx>
Date: Tue, 13 Mar 2007 08:24:12 -0400
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I understand what you're saying; it was one of the considerations
when first putting the patch together some time ago.  The console
ring was used for two reasons:  the primary reason was to get
a more WYSIWYG output.  Two input sources are inherently capable
of getting slightly out of sync (or worse).  The second reason
is that syslog can be expensive.  In the end, the WYSIWYG and
cost resulted in the console ring approach.

Would this be more acceptable if it were selectable ?  That is,
come up with a libxc/sysctl mechanism (which should be pretty
easy) to control the gating of character data to the console ring
fom guest_console_write ?

The capability is pretty useful in remoting the vga output to
another node (and logging it).  It would be nice to find a
way to preserve current behavior (as you note), and also allow
the ability to continue to remote it.


Keir Fraser wrote:
On 12/3/07 20:14, "Ben Thomas" <bthomas@xxxxxxxxxxxxxxx> wrote:

Part of the original submission that resulted in 14287 was to catch
all output to the console/vga. 14287, as committed, only captures
a portion of the console output. The attached patch allows capture of
the rest of the output.

The console ring is only for Xen output (and also, as it happens, HVM domU
bootstrap output since bytes output via port 0xe9 also get printk'ed). The
only other useful output would be from dom0, and you can already obtain that
via syslog. By not capturing dom0 output in the console ring we prevent
interactive sessions on the dom0 console from obliterating useful Xen debug
output which we may want to gather later (if we're not running an automatic
gatherer daemon).
 -- Keir

Ben Thomas                                         Virtual Iron Software
bthomas@xxxxxxxxxxxxxxx                            Tower 1, Floor 2
978-849-1214                                       900 Chelmsford Street
                                                   Lowell, MA 01851

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