Re: [Xen-devel] [PATCH v2 2/5] xenstore: add explicit memory context parameter to get_parent()

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Jul 18, 2016 at 09:31:26AM +0200, Juergen Gross wrote:
> Add a parameter to xenstored get_parent() function to explicitly
> specify the memory context to be used for allocations. This will make
> it easier to avoid memory leaks by using a context which is freed
> soon.
> 
> When available use a temporary context when calling get_parent(),
> otherwise mimic the old behavior by calling get_parent() with the same
> argument for both parameters.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  tools/xenstore/xenstored_core.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
> index 94c809c..9448ee8 100644
> --- a/tools/xenstore/xenstored_core.c
> +++ b/tools/xenstore/xenstored_core.c
> @@ -507,12 +507,12 @@ static enum xs_perm_type perm_for_conn(struct 
> connection *conn,
>       return perms[0].perms & mask;
>  }
>  
> -static char *get_parent(const char *node)
> +static char *get_parent(const void *mem, const char *node)

I would name mem ctx or context instead. And maybe document this
function a bit saying that memory allocation is done with the first
parameter.

With those cosmetic issues fixed:

Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

>  {
>       char *slash = strrchr(node + 1, '/');
>       if (!slash)
> -             return talloc_strdup(node, "/");
> -     return talloc_asprintf(node, "%.*s", (int)(slash - node), node);
> +             return talloc_strdup(mem, "/");
> +     return talloc_asprintf(mem, "%.*s", (int)(slash - node), node);
>  }
>  
>  /* What do parents say? */
> @@ -521,7 +521,7 @@ static enum xs_perm_type ask_parents(struct connection 
> *conn, const char *name)
>       struct node *node;
>  
>       do {
> -             name = get_parent(name);
> +             name = get_parent(name, name);
>               node = read_node(conn, name);
>               if (node)
>                       break;
> @@ -816,7 +816,7 @@ static struct node *construct_node(struct connection 
> *conn, const char *name)
>       const char *base;
>       unsigned int baselen;
>       struct node *parent, *node;
> -     char *children, *parentname = get_parent(name);
> +     char *children, *parentname = get_parent(name, name);
>  
>       /* If parent doesn't exist, create it. */
>       parent = read_node(conn, parentname);
> @@ -1036,7 +1036,7 @@ static int _rm(struct connection *conn, struct node 
> *node, const char *name)
>       /* Delete from parent first, then if we crash, the worst that can
>          happen is the child will continue to take up space, but will
>          otherwise be unreachable. */
> -     struct node *parent = read_node(conn, get_parent(name));
> +     struct node *parent = read_node(conn, get_parent(name, name));
>       if (!parent) {
>               send_error(conn, EINVAL);
>               return 0;
> @@ -1073,7 +1073,7 @@ static void do_rm(struct connection *conn, struct 
> buffered_data *in)
>       if (!node) {
>               /* Didn't exist already?  Fine, if parent exists. */
>               if (errno == ENOENT) {
> -                     node = read_node(conn, get_parent(name));
> +                     node = read_node(conn, get_parent(in, name));
>                       if (node) {
>                               send_ack(conn, XS_RM);
>                               return;
> -- 
> 2.6.6
> 

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