[Qemu-devel] [PATCH 4/4] qemu-nbd: do not start the block layer in the parent

[Paolo Bonzini <pbonzini@redhat.com>]

Forking and threading do not behave very well together.  With qemu-nbd in
-c mode it could happen that the thread pool is started in the parent, and
the children (the one actually doing the I/O) is left without working I/O.
Fix this by only running bdrv_init in the child process.

Reported-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qemu-nbd.c |   31 ++++++++++++++-----------------
 1 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/qemu-nbd.c b/qemu-nbd.c
index 5031158..962952c 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -371,21 +371,6 @@ int main(int argc, char **argv)
 	return 0;
     }
 
-    bdrv_init();
-
-    bs = bdrv_new("hda");
-
-    if ((ret = bdrv_open(bs, argv[optind], flags, NULL)) < 0) {
-        errno = -ret;
-        err(EXIT_FAILURE, "Failed to bdrv_open '%s'", argv[optind]);
-    }
-
-    fd_size = bs->total_sectors * 512;
-
-    if (partition != -1 &&
-        find_partition(bs, partition, &dev_offset, &fd_size))
-        err(EXIT_FAILURE, "Could not find partition %d", partition);
-
     if (device) {
         pid_t pid;
         int sock;
@@ -418,7 +403,6 @@ int main(int argc, char **argv)
             size_t blocksize;
 
             ret = 0;
-            bdrv_close(bs);
 
             do {
                 sock = unix_socket_outgoing(socket);
@@ -473,8 +457,21 @@ int main(int argc, char **argv)
         /* children */
     }
 
+    bdrv_init();
+    bs = bdrv_new("hda");
+    if ((ret = bdrv_open(bs, argv[optind], flags, NULL)) < 0) {
+        errno = -ret;
+        err(EXIT_FAILURE, "Failed to bdrv_open '%s'", argv[optind]);
+    }
+
+    fd_size = bs->total_sectors * 512;
+
+    if (partition != -1 &&
+        find_partition(bs, partition, &dev_offset, &fd_size)) {
+        err(EXIT_FAILURE, "Could not find partition %d", partition);
+    }
+
     sharing_fds = g_malloc((shared + 1) * sizeof(int));
-
     if (socket) {
         sharing_fds[0] = unix_socket_incoming(socket);
     } else {
-- 
1.7.6.4