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

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.

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.