Re: [Qemu-devel] [PATCH -V2] iohandler: update qemu_fd_set_handler to work with null call back arg

[Anthony Liguori]

On 09/07/2011 07:30 AM, Aneesh Kumar K.V wrote:
Many users of qemu_fd_set_handler including VirtFS use NULL call back arg.
Update fd_trampoline and qemu_fd_set_handler to work with NULL call back arg
Signed-off-by: Aneesh Kumar K.V<aneesh.ku...@linux.vnet.ibm.com>
---
Changes from V1:
    Add support for dropping event source

  iohandler.c |   31 +++++++++++++------------------
  1 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/iohandler.c b/iohandler.c
index 5ef66fb..783f3ac 100644
--- a/iohandler.c
+++ b/iohandler.c
@@ -93,9 +93,8 @@ static gboolean fd_trampoline(GIOChannel *chan, GIOCondition 
cond, gpointer opaq
  {
      IOTrampoline *tramp = opaque;

-    if (tramp->opaque == NULL) {
+    if (!tramp->fd_read&&  !tramp->fd_write)
          return FALSE;
-    }

Heh, this is pretty anti-CODING_STYLE :-)

At any rate, I think this whole segment has to go.  It's easier to not 
deal with removing  sources in two places.


      if ((cond&  G_IO_IN)&&  tramp->fd_read) {
          tramp->fd_read(tramp->opaque);
@@ -113,6 +112,7 @@ int qemu_set_fd_handler(int fd,
                          IOHandler *fd_write,
                          void *opaque)
  {
+    GIOCondition cond = 0;
      static IOTrampoline fd_trampolines[FD_SETSIZE];
      IOTrampoline *tramp =&fd_trampolines[fd];

@@ -121,25 +121,20 @@ int qemu_set_fd_handler(int fd,
          g_source_remove(tramp->tag);
      }

-    if (opaque) {
-        GIOCondition cond = 0;
-
-        tramp->fd_read = fd_read;
-        tramp->fd_write = fd_write;
-        tramp->opaque = opaque;
-
-        if (fd_read) {
-            cond |= G_IO_IN | G_IO_ERR;
-        }
-
-        if (fd_write) {
-            cond |= G_IO_OUT | G_IO_ERR;
-        }
+    if (fd_read) {
+        cond |= G_IO_IN | G_IO_ERR;
+    }

-        tramp->chan = g_io_channel_unix_new(fd);
-        tramp->tag = g_io_add_watch(tramp->chan, cond, fd_trampoline, tramp);
+    if (fd_write) {
+        cond |= G_IO_OUT | G_IO_ERR;
      }

+    tramp->fd_read = fd_read;
+    tramp->fd_write = fd_write;
+    tramp->opaque = opaque;
+    tramp->chan = g_io_channel_unix_new(fd);
+    tramp->tag = g_io_add_watch(tramp->chan, cond, fd_trampoline, tramp);
+

I think this is a bit more complicated than is really needed.  Here's 
what I came up with which also fixes another bug where the io channel 
could be freed twice.  I stumbled across this via a very strange failure 
scenario.  Avi, it might be worth trying this patch to see if it fixes 
your problem too.

One thing that I found challenging debugging this, coroutines make 
valgrind very unhappy.  Is it possible that we could have a command line 
switch to fall back to the thread based coroutines so to make things 
more valgrind friendly?

diff --git a/iohandler.c b/iohandler.c
index 5ef66fb..4cc1c5a 100644
--- a/iohandler.c
+++ b/iohandler.c
@@ -93,10 +93,6 @@ static gboolean fd_trampoline(GIOChannel *chan, 
GIOCondition cond, gpointer opaq
 {
     IOTrampoline *tramp = opaque;

-    if (tramp->opaque == NULL) {
-        return FALSE;
-    }
-
     if ((cond & G_IO_IN) && tramp->fd_read) {
         tramp->fd_read(tramp->opaque);
     }
@@ -119,9 +115,10 @@ int qemu_set_fd_handler(int fd,
     if (tramp->tag != 0) {
         g_io_channel_unref(tramp->chan);
         g_source_remove(tramp->tag);
+        tramp->tag = 0;
     }

-    if (opaque) {
+    if (fd_read || fd_write || opaque) {
         GIOCondition cond = 0;

         tramp->fd_read = fd_read;

Regards,

Anthony Liguori

      return 0;
  }