async: aio_context_new(): Handle event_notifier_init failure

On a system with a low limit of open files the initialization
of the event notifier could fail and QEMU exits without printing any
error information to the user.

The problem can be easily reproduced by enforcing a low limit of open
files and start QEMU with enough I/O threads to hit this limit.

The same problem raises, without the creation of I/O threads, while
QEMU initializes the main event loop by enforcing an even lower limit of
open files.

This commit adds an error message on failure:

 # qemu [...] -object iothread,id=iothread0 -object iothread,id=iothread1
 qemu: Failed to initialize event notifier: Too many open files in system

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

12 files changed, 78 insertions, 18 deletions

diff --git a/async.c b/async.c
index a99e7f639a..6e1b282aa7 100644
--- a/async.c
+++ b/async.c
@@ -289,18 +289,24 @@ static void aio_rfifolock_cb(void *opaque)
     aio_notify(opaque);
 }
 
-AioContext *aio_context_new(void)
+AioContext *aio_context_new(Error **errp)
 {
+    int ret;
     AioContext *ctx;
     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
+    ret = event_notifier_init(&ctx->notifier, false);
+    if (ret < 0) {
+        g_source_destroy(&ctx->source);
+        error_setg_errno(errp, -ret, "Failed to initialize event notifier");
+        return NULL;
+    }
+    aio_set_event_notifier(ctx, &ctx->notifier,
+                           (EventNotifierHandler *)
+                           event_notifier_test_and_clear);
     ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
     ctx->thread_pool = NULL;
     qemu_mutex_init(&ctx->bh_lock);
     rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
-    event_notifier_init(&ctx->notifier, false);
-    aio_set_event_notifier(ctx, &ctx->notifier, 
-                           (EventNotifierHandler *)
-                           event_notifier_test_and_clear);
     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 
     return ctx;
diff --git a/include/block/aio.h b/include/block/aio.h
index 67a75ddd56..156272177f 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -102,7 +102,7 @@ void aio_set_dispatching(AioContext *ctx, bool dispatching);
  * They also provide bottom halves, a service to execute a piece of code
  * as soon as possible.
  */
-AioContext *aio_context_new(void);
+AioContext *aio_context_new(Error **errp);
 
 /**
  * aio_context_ref:
diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
index 6f0200a7ac..62c68c0f32 100644
--- a/include/qemu/main-loop.h
+++ b/include/qemu/main-loop.h
@@ -42,7 +42,7 @@
  *
  * In the case of QEMU tools, this will also start/initialize timers.
  */
-int qemu_init_main_loop(void);
+int qemu_init_main_loop(Error **errp);
 
 /**
  * main_loop_wait: Run one iteration of the main loop.
diff --git a/iothread.c b/iothread.c
index d9403cf69e..342a23fcb0 100644
--- a/iothread.c
+++ b/iothread.c
@@ -17,6 +17,7 @@
 #include "block/aio.h"
 #include "sysemu/iothread.h"
 #include "qmp-commands.h"
+#include "qemu/error-report.h"
 
 #define IOTHREADS_PATH "/objects"
 
@@ -53,6 +54,9 @@ static void iothread_instance_finalize(Object *obj)
 {
     IOThread *iothread = IOTHREAD(obj);
 
+    if (!iothread->ctx) {
+        return;
+    }
     iothread->stopping = true;
     aio_notify(iothread->ctx);
     qemu_thread_join(&iothread->thread);
@@ -63,11 +67,16 @@ static void iothread_instance_finalize(Object *obj)
 
 static void iothread_complete(UserCreatable *obj, Error **errp)
 {
+    Error *local_error = NULL;
     IOThread *iothread = IOTHREAD(obj);
 
     iothread->stopping = false;
-    iothread->ctx = aio_context_new();
     iothread->thread_id = -1;
+    iothread->ctx = aio_context_new(&local_error);
+    if (!iothread->ctx) {
+        error_propagate(errp, local_error);
+        return;
+    }
 
     qemu_mutex_init(&iothread->init_done_lock);
     qemu_cond_init(&iothread->init_done_cond);
diff --git a/main-loop.c b/main-loop.c
index 3cc79f82f9..53393a4b18 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -126,10 +126,11 @@ void qemu_notify_event(void)
 
 static GArray *gpollfds;
 
-int qemu_init_main_loop(void)
+int qemu_init_main_loop(Error **errp)
 {
     int ret;
     GSource *src;
+    Error *local_error = NULL;
 
     init_clocks();
 
@@ -138,8 +139,12 @@ int qemu_init_main_loop(void)
         return ret;
     }
 
+    qemu_aio_context = aio_context_new(&local_error);
+    if (!qemu_aio_context) {
+        error_propagate(errp, local_error);
+        return -EMFILE;
+    }
     gpollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
-    qemu_aio_context = aio_context_new();
     src = aio_get_g_source(qemu_aio_context);
     g_source_attach(src, NULL);
     g_source_unref(src);
diff --git a/qemu-img.c b/qemu-img.c
index 91d1ac3d7d..dbf0904dc0 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -2879,6 +2879,7 @@ int main(int argc, char **argv)
 {
     const img_cmd_t *cmd;
     const char *cmdname;
+    Error *local_error = NULL;
     int c;
     static const struct option long_options[] = {
         {"help", no_argument, 0, 'h'},
@@ -2893,7 +2894,12 @@ int main(int argc, char **argv)
     error_set_progname(argv[0]);
     qemu_init_exec_dir(argv[0]);
 
-    qemu_init_main_loop();
+    if (qemu_init_main_loop(&local_error)) {
+        error_report("%s", error_get_pretty(local_error));
+        error_free(local_error);
+        exit(EXIT_FAILURE);
+    }
+
     bdrv_init();
     if (argc < 2) {
         error_exit("Not enough arguments");
diff --git a/qemu-io.c b/qemu-io.c
index d2ab6946e8..66cf3ef4be 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -379,6 +379,7 @@ int main(int argc, char **argv)
     int c;
     int opt_index = 0;
     int flags = BDRV_O_UNMAP;
+    Error *local_error = NULL;
 
 #ifdef CONFIG_POSIX
     signal(SIGPIPE, SIG_IGN);
@@ -444,7 +445,11 @@ int main(int argc, char **argv)
         exit(1);
     }
 
-    qemu_init_main_loop();
+    if (qemu_init_main_loop(&local_error)) {
+        error_report("%s", error_get_pretty(local_error));
+        error_free(local_error);
+        exit(1);
+    }
     bdrv_init();
 
     /* initialize commands */
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 9bc152e6c3..de9963f8fb 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -674,7 +674,11 @@ int main(int argc, char **argv)
         snprintf(sockpath, 128, SOCKET_PATH, basename(device));
     }
 
-    qemu_init_main_loop();
+    if (qemu_init_main_loop(&local_err)) {
+        error_report("%s", error_get_pretty(local_err));
+        error_free(local_err);
+        exit(EXIT_FAILURE);
+    }
     bdrv_init();
     atexit(bdrv_close_all);
 
diff --git a/tests/test-aio.c b/tests/test-aio.c
index c6a8713e83..a7cb5c9915 100644
--- a/tests/test-aio.c
+++ b/tests/test-aio.c
@@ -14,6 +14,7 @@
 #include "block/aio.h"
 #include "qemu/timer.h"
 #include "qemu/sockets.h"
+#include "qemu/error-report.h"
 
 static AioContext *ctx;
 
@@ -810,11 +811,18 @@ static void test_source_timer_schedule(void)
 
 int main(int argc, char **argv)
 {
+    Error *local_error = NULL;
     GSource *src;
 
     init_clocks();
 
-    ctx = aio_context_new();
+    ctx = aio_context_new(&local_error);
+    if (!ctx) {
+        error_report("Failed to create AIO Context: '%s'",
+                     error_get_pretty(local_error));
+        error_free(local_error);
+        exit(1);
+    }
     src = aio_get_g_source(ctx);
     g_source_attach(src, NULL);
     g_source_unref(src);
diff --git a/tests/test-thread-pool.c b/tests/test-thread-pool.c
index ed2b25b8eb..8c4d68b345 100644
--- a/tests/test-thread-pool.c
+++ b/tests/test-thread-pool.c
@@ -4,6 +4,7 @@
 #include "block/thread-pool.h"
 #include "block/block.h"
 #include "qemu/timer.h"
+#include "qemu/error-report.h"
 
 static AioContext *ctx;
 static ThreadPool *pool;
@@ -222,10 +223,17 @@ static void test_cancel_async(void)
 int main(int argc, char **argv)
 {
     int ret;
+    Error *local_error = NULL;
 
     init_clocks();
 
-    ctx = aio_context_new();
+    ctx = aio_context_new(&local_error);
+    if (!ctx) {
+        error_report("Failed to create AIO Context: '%s'",
+                     error_get_pretty(local_error));
+        error_free(local_error);
+        exit(1);
+    }
     pool = aio_get_thread_pool(ctx);
 
     g_test_init(&argc, &argv, NULL);
diff --git a/tests/test-throttle.c b/tests/test-throttle.c
index 000ae31af9..d8ba415e43 100644
--- a/tests/test-throttle.c
+++ b/tests/test-throttle.c
@@ -14,6 +14,7 @@
 #include <math.h>
 #include "block/aio.h"
 #include "qemu/throttle.h"
+#include "qemu/error-report.h"
 
 static AioContext     *ctx;
 static LeakyBucket    bkt;
@@ -492,10 +493,17 @@ static void test_accounting(void)
 int main(int argc, char **argv)
 {
     GSource *src;
+    Error *local_error = NULL;
 
     init_clocks();
 
-    ctx = aio_context_new();
+    ctx = aio_context_new(&local_error);
+    if (!ctx) {
+        error_report("Failed to create AIO Context: '%s'",
+                     error_get_pretty(local_error));
+        error_free(local_error);
+        exit(1);
+    }
     src = aio_get_g_source(ctx);
     g_source_attach(src, NULL);
     g_source_unref(src);
diff --git a/vl.c b/vl.c
index dc792fe08b..6d073c3576 100644
--- a/vl.c
+++ b/vl.c
@@ -2968,6 +2968,7 @@ int main(int argc, char **argv, char **envp)
     ram_addr_t maxram_size = default_ram_size;
     uint64_t ram_slots = 0;
     FILE *vmstate_dump_file = NULL;
+    Error *main_loop_err = NULL;
 
     atexit(qemu_run_exit_notifiers);
     error_set_progname(argv[0]);
@@ -3998,8 +3999,8 @@ int main(int argc, char **argv, char **envp)
 
     os_daemonize();
 
-    if (qemu_init_main_loop()) {
-        fprintf(stderr, "qemu_init_main_loop failed\n");
+    if (qemu_init_main_loop(&main_loop_err)) {
+        error_report("%s", error_get_pretty(main_loop_err));
         exit(1);
     }