[Libguestfs] [PATCH 1/3] appliance: Pass "quiet" option to kernel when !verbose.

Pino Toscano ptoscano at redhat.com
Fri Mar 18 12:54:19 UTC 2016

On Thursday 17 March 2016 10:08:41 Richard W.M. Jones wrote:
> The quiet option suppresses kernel messages.  On my laptop it improves
> appliance boot times by about 40% (3.5s -> 2.5s).
> The emulated UART is slow and has a fixed, small FIFO (16 bytes).  But
> it has the advantage of being a simple ISA device which is available
> very early in boot, thus enabling us to diagnose early boot problems.
> So the aim is to reduce our usage of this UART on fast paths.
> Of course when we are in verbose mode, we should not add this flag
> because we want to see all the messages.
> This change is not entirely invisible:
> (1) Progress messages use the "Linux version ..." string from kernel
> output in order to determine part of where we are in the boot process.
> This string will no longer be detected.  We should probably use a BIOS
> message or maybe drop this altogether.  I have added a comment to the
> code.
> (2) It is possible for programs to be listening for
> GUESTFS_EVENT_APPLIANCE events, and they will see fewer messages now
> (although what kernel messages programs see is never defined).

From what I see, these events were sent only after 5 seconds from the
launch, so users of the library should (theoretically of course) be
already prepared to not receive them.  I guess that this could be
mentioned in the commit message.

Pino Toscano
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