[PATCH] block/rbd: report a better error when namespace does not exist

[Stefano Garzarella <sgarzare@redhat.com>]

If the namespace does not exist, rbd_create() fails with -ENOENT and
QEMU reports a generic "error rbd create: No such file or directory":

    $ qemu-img create rbd:rbd/namespace/image 1M
    Formatting 'rbd:rbd/namespace/image', fmt=raw size=1048576
    qemu-img: rbd:rbd/namespace/image: error rbd create: No such file or directory

Unfortunately rados_ioctx_set_namespace() does not fail if the namespace
does not exist, so let's use rbd_namespace_exists() in qemu_rbd_connect()
to check if the namespace exists, reporting a more understandable error:

    $ qemu-img create rbd:rbd/namespace/image 1M
    Formatting 'rbd:rbd/namespace/image', fmt=raw size=1048576
    qemu-img: rbd:rbd/namespace/image: namespace 'namespace' does not exist

Reported-by: Tingting Mao <timao@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 meson.build |  6 ++++++
 block/rbd.c | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/meson.build b/meson.build
index 9b20dcd143..e6c0afd62b 100644
--- a/meson.build
+++ b/meson.build
@@ -1828,6 +1828,12 @@ config_host_data.set('HAVE_GETIFADDRS', cc.has_function('getifaddrs'))
 config_host_data.set('HAVE_OPENPTY', cc.has_function('openpty', dependencies: util))
 config_host_data.set('HAVE_STRCHRNUL', cc.has_function('strchrnul'))
 config_host_data.set('HAVE_SYSTEM_FUNCTION', cc.has_function('system', prefix: '#include <stdlib.h>'))
+if rbd.found()
+  config_host_data.set('HAVE_RBD_NAMESPACE_EXISTS',
+                       cc.has_function('rbd_namespace_exists',
+                                       dependencies: rbd,
+                                       prefix: '#include <rbd/librbd.h>'))
+endif
 if rdma.found()
   config_host_data.set('HAVE_IBV_ADVISE_MR',
                        cc.has_function('ibv_advise_mr',
diff --git a/block/rbd.c b/block/rbd.c
index 6caf35cbba..0ff23c5b26 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -831,6 +831,26 @@ static int qemu_rbd_connect(rados_t *cluster, rados_ioctx_t *io_ctx,
         error_setg_errno(errp, -r, "error opening pool %s", opts->pool);
         goto failed_shutdown;
     }
+
+#ifdef HAVE_RBD_NAMESPACE_EXISTS
+    if (opts->has_q_namespace && strlen(opts->q_namespace) > 0) {
+        bool exists;
+
+        r = rbd_namespace_exists(*io_ctx, opts->q_namespace, &exists);
+        if (r != 0) {
+            error_setg_errno(errp, -r, "error checking namespace");
+            goto failed_ioctx_destroy;
+        }
+
+        if (!exists) {
+            error_setg(errp, "namespace '%s' does not exist",
+                       opts->q_namespace);
+            r = -ENOENT;
+            goto failed_ioctx_destroy;
+        }
+    }
+#endif
+
     /*
      * Set the namespace after opening the io context on the pool,
      * if nspace == NULL or if nspace == "", it is just as we did nothing
@@ -840,6 +860,10 @@ static int qemu_rbd_connect(rados_t *cluster, rados_ioctx_t *io_ctx,
     r = 0;
     goto out;
 
+#ifdef HAVE_RBD_NAMESPACE_EXISTS
+failed_ioctx_destroy:
+    rados_ioctx_destroy(*io_ctx);
+#endif
 failed_shutdown:
     rados_shutdown(*cluster);
 out:
-- 
2.35.3