[libvirt] [PATCH V3] Use loop-control to allocate loop device.
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(a)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;
+ }
+ 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
+ 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)
--
1.8.1.4