[libvirt] [PATCH 5/5] qemu: add support for sending QEMU stdout/stderr to virtlogd

[Daniel P. Berrange]

On Wed, Nov 04, 2015 at 09:17:00AM +0100, Peter Krempa wrote:
> On Tue, Nov 03, 2015 at 16:04:24 +0000, Daniel Berrange wrote:
> > Currently the QEMU stdout/stderr streams are written directly to
> > a regular file (eg /var/log/libvirt/qemu/$GUEST.log). While those
> > can be rotated by logrotate (using copytruncate option) this is
> > not very efficient. It also leaves open a window of opportunity
> > for a compromised/broken QEMU to DOS the host filesystem by
> > writing lots of text to stdout/stderr.
> > 
> > This makes it possible to connect the stdout/stderr file handles
> > to a pipe that is provided by virtlogd. The virtlogd daemon will
> > read from this pipe and write data to the log file, performing
> > file rotation whenever a pre-determined size limit is reached.
> > 
> > Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
> > ---
> >  cfg.mk                             |  2 +-
> >  src/qemu/libvirtd_qemu.aug         |  1 +
> >  src/qemu/qemu.conf                 | 15 +++++++++++++
> >  src/qemu/qemu_conf.c               | 18 ++++++++++++++++
> >  src/qemu/qemu_conf.h               |  1 +
> >  src/qemu/qemu_domain.c             | 43 +++++++++++++++++++++++++++++++-------
> >  src/qemu/qemu_process.c            | 42 +++++++++++++++++++++----------------
> >  src/qemu/test_libvirtd_qemu.aug.in |  1 +
> >  8 files changed, 96 insertions(+), 27 deletions(-)
> > 
> 
> [...]
> 
> > diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> > index f744419..e72ca20 100644
> > --- a/src/qemu/qemu_process.c
> > +++ b/src/qemu/qemu_process.c
> > @@ -4774,7 +4774,10 @@ int qemuProcessStart(virConnectPtr conn,
> >  
> >      qemuDomainObjCheckTaint(driver, vm, logfile);
> >  
> > -    if ((pos = lseek(logfile, 0, SEEK_END)) < 0)
> > +    /* When using logd, the logfile FD is a pipe which is
> > +     * not seekable... */
> > +    if (!cfg->stdioLogD &&
> > +        (pos = lseek(logfile, 0, SEEK_END)) < 0)
> >          VIR_WARN("Unable to seek to end of logfile: %s",
> >                   virStrerror(errno, ebuf, sizeof(ebuf)));
> 
> This will break the code that is in place to read the qemu log file in
> case of a early qemu startup failure so that we can report a semi-useful
> error message.
> 
> Additionally in case where you don't use QMP and qemu does not support
> chardev info retrieval, this will also break the lookup of the PTYs for
> serials/parallels/channels. As a solution here I'd rather see that we
> drop support for such old qemus finally and not have to care about it
> any more.
> 
> We probably need a set of APIs here, that will allow you to mark a place
> in the logfile and a second API that will allow to retrieve the data
> between the marker and the end.

Well, solving all that was incredibly painful :-) After re-writing it
3 times, I've now got a satisfactory solution that refactors all this
log handling code in the QEMU driver....

Regards,
Daniel
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