[Qemu-devel] [PATCH v3] char: restore read callback on a reattached (hotplug) chardev

[Qemu-devel] [PATCH v3] char: restore read callback on a reattached (hotplug) chardev

[Gal Hammer]

Fix a bug that was introduced in commit 386a5a1e. A removal of a device
set the chr handlers to NULL. However when the device is plugged back,
its read callback is not restored so data can't be transftered from the
host to the guest (e.g. via the virtio-serial port).

https://bugzilla.redhat.com/show_bug.cgi?id=1027181

Signed-off-by: Gal Hammer <ghammer@redhat.com>

V3: - fix a typo in comment.
    - move the revision history after the "signed-off-by" tag.

V2: - do not call chr_update_read_handler on device removal.
    - add asserts to verify chr_update_read_handler is not called
      with an assigned fd_in_tag to prevent fd leaks.
    - update fd and udp backends' chr_update_read_handler function
      so it won't remove fd_in to prevent a double release.
---
 qemu-char.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/qemu-char.c b/qemu-char.c
index e00f84c..69649f0 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -213,7 +213,7 @@ void qemu_chr_add_handlers(CharDriverState *s,
     s->chr_read = fd_read;
     s->chr_event = fd_event;
     s->handler_opaque = opaque;
-    if (s->chr_update_read_handler)
+    if (fe_open && s->chr_update_read_handler)
         s->chr_update_read_handler(s);
 
     if (!s->explicit_fe_open) {
@@ -870,6 +870,7 @@ static void fd_chr_update_read_handler(CharDriverState *chr)
 {
     FDCharDriver *s = chr->opaque;
 
+    assert(!chr->fd_in_tag);
     remove_fd_in_watch(chr);
     if (s->fd_in) {
         chr->fd_in_tag = io_add_watch_poll(s->fd_in, fd_chr_read_poll,
@@ -2228,7 +2229,7 @@ static void udp_chr_update_read_handler(CharDriverState *chr)
 {
     NetCharDriver *s = chr->opaque;
 
-    remove_fd_in_watch(chr);
+    assert(!chr->fd_in_tag);
     if (s->chan) {
         chr->fd_in_tag = io_add_watch_poll(s->chan, udp_chr_read_poll,
                                            udp_chr_read, chr);
@@ -2510,6 +2511,17 @@ static void tcp_chr_connect(void *opaque)
     qemu_chr_be_generic_open(chr);
 }
 
+static void tcp_chr_update_read_handler(CharDriverState *chr)
+{
+    TCPCharDriver *s = chr->opaque;
+
+    assert(!chr->fd_in_tag);
+    if (s->chan && !chr->fd_in_tag) {
+        chr->fd_in_tag = io_add_watch_poll(s->chan, tcp_chr_read_poll,
+                                           tcp_chr_read, chr);
+    }
+}
+
 #define IACSET(x,a,b,c) x[0] = a; x[1] = b; x[2] = c;
 static void tcp_chr_telnet_init(int fd)
 {
@@ -2665,6 +2677,7 @@ static CharDriverState *qemu_chr_open_socket_fd(int fd, bool do_nodelay,
     chr->get_msgfd = tcp_get_msgfd;
     chr->chr_add_client = tcp_chr_add_client;
     chr->chr_add_watch = tcp_chr_add_watch;
+    chr->chr_update_read_handler = tcp_chr_update_read_handler;
     /* be isn't opened until we get a connection */
     chr->explicit_be_open = true;
 
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH v3] char: restore read callback on a reattached (hotplug) chardev

[Markus Armbruster]

Gal Hammer <ghammer@redhat.com> writes:

> Fix a bug that was introduced in commit 386a5a1e. A removal of a device
> set the chr handlers to NULL. However when the device is plugged back,
> its read callback is not restored so data can't be transftered from the
> host to the guest (e.g. via the virtio-serial port).
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1027181
>
> Signed-off-by: Gal Hammer <ghammer@redhat.com>
>
> V3: - fix a typo in comment.
>     - move the revision history after the "signed-off-by" tag.

Close, but no cigar :)

It needs to go below the '---' line.

> V2: - do not call chr_update_read_handler on device removal.
>     - add asserts to verify chr_update_read_handler is not called
>       with an assigned fd_in_tag to prevent fd leaks.
>     - update fd and udp backends' chr_update_read_handler function
>       so it won't remove fd_in to prevent a double release.
> ---

Right here is fine.

>  qemu-char.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
[...]

Re: [Qemu-devel] [PATCH v3] char: restore read callback on a reattached (hotplug) chardev

[Eric Blake]

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On 12/12/2013 05:02 AM, Markus Armbruster wrote:
> Gal Hammer <ghammer@redhat.com> writes:
> 
>> Fix a bug that was introduced in commit 386a5a1e. A removal of a device
>> set the chr handlers to NULL. However when the device is plugged back,
>> its read callback is not restored so data can't be transftered from the

[1]

>> host to the guest (e.g. via the virtio-serial port).
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=1027181
>>
>> Signed-off-by: Gal Hammer <ghammer@redhat.com>
>>
>> V3: - fix a typo in comment.
>>     - move the revision history after the "signed-off-by" tag.
> 
> Close, but no cigar :)

Also, you missed my suggested typo fix at [1].
  s/transftered/transferred/

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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