Re: [Xen-devel] [PATCH 2/3] python: Extract registered watch search logic from xspy_read_watch()

[Wei Liu]

On Fri, Sep 15, 2017 at 05:35:35PM +0100, Euan Harris wrote:
>  tools/python/xen/lowlevel/xs/xs.c | 61 
> ---
>  1 file changed, 38 insertions(+), 23 deletions(-)
> 
> diff --git a/tools/python/xen/lowlevel/xs/xs.c 
> b/tools/python/xen/lowlevel/xs/xs.c
> index 9f1b916..a4b50a0 100644
> --- a/tools/python/xen/lowlevel/xs/xs.c
> +++ b/tools/python/xen/lowlevel/xs/xs.c
> @@ -77,6 +77,8 @@ static inline struct xs_handle *xshandle(XsHandle *self)
>  
>  static void remove_watch(XsHandle *xsh, PyObject *token);
>  
> +static PyObject *match_watch_by_token(XsHandle *self, char **xsval);
> +
>  static PyObject *none(bool result);
>  
>  static int parse_transaction_path(XsHandle *self, PyObject *args,
> @@ -484,8 +486,6 @@ static PyObject *xspy_read_watch(XsHandle *self, PyObject 
> *args)
>  struct xs_handle *xh = xshandle(self);
>  PyObject *val = NULL;
>  char **xsval;
> -PyObject *token;
> -int i;
>  unsigned int num;
>  
>  if (!xh)
> @@ -497,32 +497,20 @@ again:
>  Py_END_ALLOW_THREADS
>  if (!xsval) {
>  PyErr_SetFromErrno(xs_error);
> -goto exit;
> -}
> -if (sscanf(xsval[XS_WATCH_TOKEN], "%li", (unsigned long *)) != 1) {
> - xs_set_error(EINVAL);
> -goto exit;
> -}
> -for (i = 0; i < PyList_Size(self->watches); i++) {
> -if (token == PyList_GetItem(self->watches, i))
> -break;
> -}
> -if (i == PyList_Size(self->watches)) {
> -  /* We do not have a registered watch for the one that has just fired.
> - Ignore this -- a watch that has been recently deregistered can still
> - have watches in transit.  This is a blocking method, so go back to
> - read again.
> -  */
> -  free(xsval);
> -  goto again;
> +return val;
>  }
> -/* Create tuple (path, token). */
> -val = Py_BuildValue("(sO)", xsval[XS_WATCH_PATH], token);
> - exit:
> +
> +val = match_watch_by_token(self, xsval);
>  free(xsval);
> +
> +if (!val && errno == EAGAIN) {
> +goto again;
> +}
> +
>  return val;
>  }
>  
> +

Stray blank line.

>  #define xspy_unwatch_doc "\n"\
>   "Stop watching a path.\n"   \
>   " path  [string] : xenstore path.\n"\
> @@ -868,6 +856,33 @@ static int parse_transaction_path(XsHandle *self, 
> PyObject *args,
>  }
>  
>  
> +static PyObject *match_watch_by_token(XsHandle *self, char **xsval)
> +{
> +PyObject *token;
> +int i;
> +
> +if (sscanf(xsval[XS_WATCH_TOKEN], "%li", (unsigned long *)) != 1) {
> + xs_set_error(EINVAL);

Please fix indentation here.

With the comments addressed:

Reviewed-by: Wei Liu 

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[Xen-devel] [PATCH 2/3] python: Extract registered watch search logic from xspy_read_watch()

[Euan Harris]

When a watch fires, xspy_read_watch() checks whether the client has
registered interest in the path which changed and, if so, returns the
path and a client-supplied token.   The binding for xs_check_watch()
needs to do the same, so this patch extracts the search code into a
separate function.

Signed-off-by: Euan Harris 
---
 tools/python/xen/lowlevel/xs/xs.c | 61 ---
 1 file changed, 38 insertions(+), 23 deletions(-)

diff --git a/tools/python/xen/lowlevel/xs/xs.c 
b/tools/python/xen/lowlevel/xs/xs.c
index 9f1b916..a4b50a0 100644
--- a/tools/python/xen/lowlevel/xs/xs.c
+++ b/tools/python/xen/lowlevel/xs/xs.c
@@ -77,6 +77,8 @@ static inline struct xs_handle *xshandle(XsHandle *self)
 
 static void remove_watch(XsHandle *xsh, PyObject *token);
 
+static PyObject *match_watch_by_token(XsHandle *self, char **xsval);
+
 static PyObject *none(bool result);
 
 static int parse_transaction_path(XsHandle *self, PyObject *args,
@@ -484,8 +486,6 @@ static PyObject *xspy_read_watch(XsHandle *self, PyObject 
*args)
 struct xs_handle *xh = xshandle(self);
 PyObject *val = NULL;
 char **xsval;
-PyObject *token;
-int i;
 unsigned int num;
 
 if (!xh)
@@ -497,32 +497,20 @@ again:
 Py_END_ALLOW_THREADS
 if (!xsval) {
 PyErr_SetFromErrno(xs_error);
-goto exit;
-}
-if (sscanf(xsval[XS_WATCH_TOKEN], "%li", (unsigned long *)) != 1) {
-   xs_set_error(EINVAL);
-goto exit;
-}
-for (i = 0; i < PyList_Size(self->watches); i++) {
-if (token == PyList_GetItem(self->watches, i))
-break;
-}
-if (i == PyList_Size(self->watches)) {
-  /* We do not have a registered watch for the one that has just fired.
- Ignore this -- a watch that has been recently deregistered can still
- have watches in transit.  This is a blocking method, so go back to
- read again.
-  */
-  free(xsval);
-  goto again;
+return val;
 }
-/* Create tuple (path, token). */
-val = Py_BuildValue("(sO)", xsval[XS_WATCH_PATH], token);
- exit:
+
+val = match_watch_by_token(self, xsval);
 free(xsval);
+
+if (!val && errno == EAGAIN) {
+goto again;
+}
+
 return val;
 }
 
+
 #define xspy_unwatch_doc "\n"  \
"Stop watching a path.\n"   \
" path  [string] : xenstore path.\n"\
@@ -868,6 +856,33 @@ static int parse_transaction_path(XsHandle *self, PyObject 
*args,
 }
 
 
+static PyObject *match_watch_by_token(XsHandle *self, char **xsval)
+{
+PyObject *token;
+int i;
+
+if (sscanf(xsval[XS_WATCH_TOKEN], "%li", (unsigned long *)) != 1) {
+   xs_set_error(EINVAL);
+return NULL;
+}
+for (i = 0; i < PyList_Size(self->watches); i++) {
+if (token == PyList_GetItem(self->watches, i))
+break;
+}
+if (i == PyList_Size(self->watches)) {
+/* We do not have a registered watch for the one that has just fired.
+   Ignore this -- a watch that has been recently deregistered can still
+   have watches in transit.
+*/
+xs_set_error(EAGAIN);
+return NULL;
+}
+
+/* Create tuple (path, token). */
+return Py_BuildValue("(sO)", xsval[XS_WATCH_PATH], token);
+}
+
+
 static PyObject *none(bool result)
 {
 if (result) {
-- 
1.8.3.1


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