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

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(a)redhat.com&gt; > > --- > > 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. Ohh, yes, I should have known this was useful for something really :-) > 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. So this relies on the 'info chardev' command which was added in: commit 5ccfae10a79e52654c9edc68da6d05f29466b4f9 Author: aliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162> Date: Fri Oct 31 17:31:29 2008 +0000 Implement "info chardev" command. (Gerd Hoffmann) This is QEMU v1.0 or later. Given that it is 7 years old, I think we are justified in raising our min QEMU version to 1.0. There's probably a fair bit of other cruft we'll kill by doing this.