On Tue, Aug 27, 2013 at 11:51:29AM -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.

Signed-off-by: Ian Main <imain@redhat.com> --- configure.ac | 12 +++++++++ src/util/virfile.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 84 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..22a0db5 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; + } + 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 +650,28 @@ cleanup: return fd; }

+static int virFileLoopDeviceOpen(char **dev_name) +{ + int loop_fd = -1; + +#ifdef HAVE_DECL_LOOP_CTL_GET_FREE + 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) { + VIR_WARN("loop-control allocation failed, trying search technique."); + } else { + return loop_fd; + }

We don't really need to VIR_WARN here - it is an expected scenario on old kernels. We're already logging the loop_fd value above, so I'd change this if/else pair to be simply: 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)

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