[libvirt] [PATCH] qemu: Handle huge number of queues correctly

[Michal Privoznik]

Currently, kernel supports up to 8 queues for a multiqueue tap device.
However, if user tries to enter a huge number (e.g. one million) the tap
allocation fails, as expected. But what is not expected is the log full
of warnings:

    warning : virFileClose:83 : Tried to close invalid fd 0

The problem is, upon error we iterate over an array of FDs (handlers to
queues) and VIR_FORCE_CLOSE() over each item. However, the array is
pre-filled with zeros. Hence, we repeatedly close stdin. Ouch.
But there's more. The queues allocation is done in virNetDevTapCreate()
which cleans up the FDs in case of error. Then, its caller, the
virNetDevTapCreateInBridgePort() iterates over the FD array and tries to
close them too. And so does qemuNetworkIfaceConnect() and
qemuBuildInterfaceCommandLine().

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_command.c | 10 +++++++---
 src/util/virnetdevtap.c |  4 ++--
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index f8fccea..73a13b3 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -405,7 +405,7 @@ qemuNetworkIfaceConnect(virDomainDefPtr def,
 cleanup:
     if (ret < 0) {
         size_t i;
-        for (i = 0; i < *tapfdSize; i++)
+        for (i = 0; i < *tapfdSize && tapfd[i] >= 0; i++)
             VIR_FORCE_CLOSE(tapfd[i]);
         if (template_ifname)
             VIR_FREE(net->ifname);
@@ -7241,6 +7241,8 @@ qemuBuildInterfaceCommandLine(virCommandPtr cmd,
             VIR_ALLOC_N(tapfdName, tapfdSize) < 0)
             goto cleanup;
 
+        memset(tapfd, -1, tapfdSize * sizeof(tapfd[0]));
+
         if (qemuNetworkIfaceConnect(def, conn, driver, net,
                                     qemuCaps, tapfd, &tapfdSize) < 0)
             goto cleanup;
@@ -7268,6 +7270,8 @@ qemuBuildInterfaceCommandLine(virCommandPtr cmd,
             VIR_ALLOC_N(vhostfdName, vhostfdSize))
             goto cleanup;
 
+        memset(vhostfd, -1, vhostfdSize * sizeof(vhostfd[0]));
+
         if (qemuOpenVhostNet(def, net, qemuCaps, vhostfd, &vhostfdSize) < 0)
             goto cleanup;
     }
@@ -7329,13 +7333,13 @@ qemuBuildInterfaceCommandLine(virCommandPtr cmd,
 cleanup:
     if (ret < 0)
         virDomainConfNWFilterTeardown(net);
-    for (i = 0; tapfd && i < tapfdSize; i++) {
+    for (i = 0; tapfd && i < tapfdSize && tapfd[i] >= 0; i++) {
         if (ret < 0)
             VIR_FORCE_CLOSE(tapfd[i]);
         if (tapfdName)
             VIR_FREE(tapfdName[i]);
     }
-    for (i = 0; vhostfd && i < vhostfdSize; i++) {
+    for (i = 0; vhostfd && i < vhostfdSize && vhostfd[i] >= 0; i++) {
         if (ret < 0)
             VIR_FORCE_CLOSE(vhostfd[i]);
         if (vhostfdName)
diff --git a/src/util/virnetdevtap.c b/src/util/virnetdevtap.c
index 42e8dfe..dc2c224 100644
--- a/src/util/virnetdevtap.c
+++ b/src/util/virnetdevtap.c
@@ -498,8 +498,8 @@ int virNetDevTapCreateInBridgePort(const char *brname,
     return 0;
 
 error:
-    while (tapfdSize)
-        VIR_FORCE_CLOSE(tapfd[--tapfdSize]);
+    while (tapfdSize && tapfd[--tapfdSize] >= 0)
+        VIR_FORCE_CLOSE(tapfd[tapfdSize]);
 
     return -1;
 }
-- 
1.8.1.5