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    SubjectRe: RFC: android logger feedback request
    On 12/21/2011 05:47 PM, Greg KH wrote:
    > On Wed, Dec 21, 2011 at 05:32:36PM -0800, Tim Bird wrote:
    >> On 12/21/2011 04:51 PM, Greg KH wrote:
    >>> On Wed, Dec 21, 2011 at 04:36:21PM -0800, Tim Bird wrote:
    >>>> On 12/21/2011 03:19 PM, Greg KH wrote:
    >>> Huh, I'm not talking about syslogd, I'm talking about the syslog(2)
    >>> syscall we have.
    >> OK - switching gears. Since the kernel log buffer isn't normally
    >> used to store use-space messages, I thought you were referring
    >> to syslog(3) and the associated (logger(1) and syslogd(8)).
    > The kernel log buffer has been storing userspace messages for a while
    > now, look at your boot log on the latest Fedora and openSUSE releases
    > (or any other distro using systemd for booting).

    Sorry - I don't have a distro that uses systemd.
    I'm completely unaware of this use of the kernel log for user-space
    message logging. No wonder Lennart and Kay
    are so hot on making a new logging system. It seems sub-optimal
    to me, to intermingle a structured log with a pure-ASCII log.

    > Again, please see what we are already doing in the kernel and userspace,
    > I think a lot of the above is already implemented.

    I don't know what systemd has got going on in user-space. I'm looking
    at a very recent kernel, and I see no support for multiple log channels,
    or an optimized open/write path.

    Maybe Lennart could save me some time doing this research.


    How does current systemd prevent user-space messages from crowding
    out kernel messages? (or vice-versa). Since you've been doing
    a lot of work on logging, do you have any existing metrics for logging
    overhead via the kernel log buffer?

    > Which brings me back to my original question, what does this code do,
    > that is not already present in the kernel, and why is a totally new
    > interface being proposed for it?

    At the least, it supports multiple log channels. Quite frankly my mind
    has been blown a bit by the suggestion to overload the kernel log buffer
    with user-space messages. I would never have gone that route. But I'll have
    to find out more about this systemd thing to answer your question.

    Secondly, this is not a particularly new or radical interface. It is new
    to legacy Linux, but it's been in the Android Linux kernel for some years
    now, and it has worked well.
    -- Tim

    Tim Bird
    Architecture Group Chair, CE Workgroup of the Linux Foundation
    Senior Staff Engineer, Sony Network Entertainment

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