Re: [libvirt] [PATCH] Use loop-control to allocate loopback device.

On Tue, Aug 27, 2013 at 03:28:07PM +0100, Daniel P. Berrange wrote: > On Mon, Aug 26, 2013 at 12:30:39PM -0700, Ian Main wrote: > > This patch changes virFileLoopDeviceOpen() to use the new loop-control > > device to allocate a new loop device. If this behavior is unsupported > > or an error occurs while trying to do this it falls back to the previous > > method of searching /dev for a free device. > > > > With this patch you can start as many image based LXC domains as you > > like (well almost). > > > > Fixes bug https://bugzilla.redhat.com/show_bug.cgi?id=995543 > > > > Signed-off-by: Ian Main <imain(a)redhat.com&gt; > > --- > > configure.ac | 12 +++++++++++ > > src/util/virfile.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++- > > 2 files changed, 72 insertions(+), 1 deletion(-) > > > > > > #if defined(__linux__) && HAVE_DECL_LO_FLAGS_AUTOCLEAR > > -static int virFileLoopDeviceOpen(char **dev_name) > > + > > +#if HAVE_DECL_LOOP_CTL_GET_FREE > > +static int virFileLoopDeviceOpenLoopCtl(char **dev_name) > > +{ > > + int fd = -1; > > + int devnr; > > + char *looppath = NULL; > > + > > + VIR_DEBUG("Opening loop-control device"); > > + if ((fd = open("/dev/loop-control", O_RDWR)) < 0) { > > + virReportSystemError(errno, "%s", > > + _("Unable to open /dev/loop-control")); > > + return -1; > > We need to distinguish ENOENT (which should be non-fatal) from > other (fatal) errors here. > > I'd suggest that we add an 'int *fd' parameter to this method, > and use the return value to indicate success / failure only. > > eg, > > if (virFileLoopDeviceOpenLoopCtl(devname, &fd) < 0) > return -1; > if (fd == -1) > fd = virFileLoopDeviceOpenSearch(devname); > return fd; You bet. To be clear does this mean you don't want to fall back to the search method in the case of an error while using loop-control allocation? My thinking was we'd just give it a go regardless of the issue..