rbd-nbd: fix unused nbd device search bug in container

In some container scenarios, the host may choose to
map a specific nbd device, for example, /dev/nbd6 into the
container, in that case, the nbd device available in the
container is not numbered from 0. The current unused
nbd device search function will return no result.
This patch fixes it.

Fixes: http://tracker.ceph.com/issues/22012
Signed-off-by: Li Wang <laurence.liwang@gmail.com>
Reviewed-by: Yunchuan Wen <yunchuan.wen@kylin-cloud.com>
(cherry picked from commit be0f9581f9727187ca03232e0b368e7da7a60609)

diff --git a/src/tools/rbd_nbd/rbd-nbd.cc b/src/tools/rbd_nbd/rbd-nbd.cc
index 16c94ea785ec591ed7d7cdf0ebd35f9707917aff..8ac38622f7b9e9d16182f9883123ac62e6b2253e 100644 (file)
--- a/src/tools/rbd_nbd/rbd-nbd.cc
+++ b/src/tools/rbd_nbd/rbd-nbd.cc
@@ -610,12 +610,27 @@ static int do_map(int argc, const char *argv[], Config *cfg)
   if (cfg->devpath.empty()) {
     char dev[64];
     bool try_load_module = true;
+    const char *path = "/sys/module/nbd/parameters/nbds_max";
+    int nbds_max = -1;
+    if (access(path, F_OK) == 0) {
+      std::ifstream ifs;
+      ifs.open(path, std::ifstream::in);
+      if (ifs.is_open()) {
+        ifs >> nbds_max;
+        ifs.close();
+      }
+    }
+
     while (true) {
       snprintf(dev, sizeof(dev), "/dev/nbd%d", index);
 
       nbd = open_device(dev, cfg, try_load_module);
       try_load_module = false;
       if (nbd < 0) {
+        if (nbd == -EPERM && nbds_max != -1 && index < (nbds_max-1)) {
+          ++index;
+          continue;
+        }
         r = nbd;
         cerr << "rbd-nbd: failed to find unused device" << std::endl;
         goto close_fd;