[libvirt] [PATCH V3] Use loop-control to allocate loop device.
Ian Main
imain at redhat.com
Mon Sep 9 19:34:20 UTC 2013
On Thu, Sep 05, 2013 at 12:33:44PM +0100, Daniel P. Berrange wrote:
> On Tue, Sep 03, 2013 at 11:45:51AM -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
> > we fall 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
> >
> > V2:
> > - Modified to use a dedicated error return for loop-control allocation
> > function.
> > - Only do fallback if /dev/loop-control does not exist, otherwise return
> > error.
> >
> > V3:
> > - Remove warning about falling back to search technique.
> >
> > Signed-off-by: Ian Main <imain at redhat.com>
> > ---
> > configure.ac | 12 ++++++++++
> > src/util/virfile.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
> > 2 files changed, 81 insertions(+), 1 deletion(-)
> >
> > diff --git a/configure.ac b/configure.ac
> > index ac8cfa1..10cd872 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -913,6 +913,18 @@ if test "$with_lxc" = "yes" || test "$with_lxc" = "check"; then
> > AC_MSG_ERROR([Required kernel features for LXC were not found])
> > fi
> > ])
> > + AC_LINK_IFELSE([AC_LANG_PROGRAM(
> > + [[
> > + #include <sched.h>
> > + #include <linux/loop.h>
> > + #include <sys/epoll.h>
> > + ]], [[
> > + unshare(!(LOOP_CTL_GET_FREE));
> > + ]])], [
> > + AC_DEFINE([HAVE_DECL_LOOP_CTL_GET_FREE], [1],
> > + [Define to 1 if you have the declaration of `LOOP_CTL_GET_FREE',
> > + and to 0 if you don't.])
> > + ])
> > fi
> > if test "$with_lxc" = "yes" ; then
> > AC_DEFINE_UNQUOTED([WITH_LXC], 1, [whether LXC driver is enabled])
> > diff --git a/src/util/virfile.c b/src/util/virfile.c
> > index 2b07ac9..9d42380 100644
> > --- a/src/util/virfile.c
> > +++ b/src/util/virfile.c
> > @@ -528,7 +528,56 @@ int virFileUpdatePerm(const char *path,
> >
> >
> > #if defined(__linux__) && HAVE_DECL_LO_FLAGS_AUTOCLEAR
> > -static int virFileLoopDeviceOpen(char **dev_name)
> > +
> > +#if HAVE_DECL_LOOP_CTL_GET_FREE
> > +
> > +/* virFileLoopDeviceOpenLoopCtl() returns -1 when a real failure has occured
> > + * while in the process of allocating or opening the loop device. On success
> > + * we return 0 and modify the fd to the appropriate file descriptor.
> > + * If /dev/loop-control does not exist, we return 0 and do not set fd. */
> > +
> > +static int virFileLoopDeviceOpenLoopCtl(char **dev_name, int *fd)
> > +{
> > + int devnr;
> > + int ctl_fd;
> > + char *looppath = NULL;
> > +
> > + VIR_DEBUG("Opening loop-control device");
> > + if ((ctl_fd = open("/dev/loop-control", O_RDWR)) < 0) {
> > + virReportSystemError(errno, "%s",
> > + _("Unable to open /dev/loop-control"));
> > + if (errno == ENOENT) {
> > + return 0;
> > + }
>
> The virReportSystemError needs to come after the errno check
> so we only report the error in the fatal code path.
>
> > + return -1;
> > + }
> > +
> > + if ((devnr = ioctl(ctl_fd, LOOP_CTL_GET_FREE)) < 0) {
> > + virReportSystemError(errno, "%s",
> > + _("Unable to get free loop device via ioctl"));
> > + close(ctl_fd);
> > + return -1;
> > + }
> > + close(ctl_fd);
> > +
> > + VIR_DEBUG("Found free loop device number %i", devnr);
> > +
> > + if (virAsprintf(&looppath, "/dev/loop%i", devnr) < 0)
> > + return -1;
> > +
> > + if ((*fd = open(looppath, O_RDWR)) < 0) {
> > + virReportSystemError(errno,
> > + _("Unable to open %s"), looppath);
> > + VIR_FREE(looppath);
> > + return -1;
> > + }
> > +
> > + *dev_name = looppath;
> > + return 0;
> > +}
> > +#endif /* HAVE_DECL_LOOP_CTL_GET_FREE */
> > +
> > +static int virFileLoopDeviceOpenSearch(char **dev_name)
> > {
> > int fd = -1;
> > DIR *dh = NULL;
> > @@ -601,6 +650,25 @@ cleanup:
> > return fd;
> > }
> >
> > +static int virFileLoopDeviceOpen(char **dev_name)
> > +{
> > + int loop_fd = -1;
> > +
> > +#ifdef HAVE_DECL_LOOP_CTL_GET_FREE
>
> s/ifdef/if/ since HAVE_* is either 0 or 1, never undefined
>
> > + if (virFileLoopDeviceOpenLoopCtl(dev_name, &loop_fd) < 0)
> > + return -1;
> > +
> > + VIR_DEBUG("Return from loop-control got fd %d\n", loop_fd);
> > +
> > + if (loop_fd >= 0)
> > + return loop_fd;
> > +#endif /* HAVE_DECL_LOOP_CTL_GET_FREE */
> > +
> > + /* Without the loop control device we just use the old technique. */
> > + loop_fd = virFileLoopDeviceOpenSearch(dev_name);
> > +
> > + return loop_fd;
> > +}
> >
> > int virFileLoopDeviceAssociate(const char *file,
> > char **dev)
>
> I made the two changes and pushed this.
>
>
> BTW, run 'make syntax-check' for patches on libvirt - it would have
> told you about the second error.
Thanks Daniel,
Ian
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