[Qemu-devel] [PATCH] chardev: Avoid adding duplicate chardev

[Pankaj Gupta <pagupta@redhat.com>]

Hotplugging existing char chardev with qmp, dereferences(removes) 
existing chardev. This patch avoids adding a chardev if a chardev 
with same id exists.

RH BZ 1660831: 

# (host) ls -lt /tmp/helloworld*
srwxr-xr-x.  /tmp/helloworld1
srwxr-xr-x.  /tmp/helloworld2

Before this patch:

hotplug existed chardev(channel1) in qmp:
{"execute":"chardev-add","arguments":{"id":"charchannel1","backend":{"type":"socket",
"data":{"addr":{"type":"unix", "data": {"path": "/tmp/helloworld1"}}}}}}

{"error": {"class": "GenericError", "desc": "attempt to add duplicate 
property 'charchannel1' to object (type 'container')"}}

# ls -lt /tmp/helloworld*
srwxr-xr-x. 1 root root 0 Dec 19 16:39 /tmp/helloworld2

After this patch:

{"execute":"chardev-add","arguments":{"id":"charchannel1","backend":{"type":"socket",
"data":{"addr":{"type":"unix", "data": {"path": "/tmp/helloworld1"}}}}}}
{"error": {"class": "GenericError", "desc": "Chardev 'charchannel1' already exist"}}

# ls -lt /tmp/helloworld*
srwxr-xr-x. 1 /tmp/helloworld1
srwxr-xr-x. 1 /tmp/helloworld2
 
Reported-by: Xiaohui Li <xiaohli@redhat.com>
Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
---
 chardev/char.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/chardev/char.c b/chardev/char.c
index ccba36bafb..cab0d3df16 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -985,6 +985,12 @@ ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
     ChardevReturn *ret;
     Chardev *chr;
 
+    chr = qemu_chr_find(id);
+    if (chr) {
+        error_setg(errp, "Chardev '%s' already exist", id);
+        return NULL;
+    }
+
     cc = char_get_class(ChardevBackendKind_str(backend->type), errp);
     if (!cc) {
         return NULL;
-- 
2.14.3