From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

vchan server creates XenStore entries to advertise its event channel and
ring, but those are not removed after the server quits.
Add additional cleanup step, so those are removed, so clients do not try
to connect to a non-existing server.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

---
Since v1:
- add NULL check after strdup
---
 tools/include/libxenvchan.h |  5 +++++
 tools/libs/vchan/init.c     | 25 +++++++++++++++++++++++++
 tools/libs/vchan/io.c       |  4 ++++
 tools/libs/vchan/vchan.h    | 31 +++++++++++++++++++++++++++++++
 4 files changed, 65 insertions(+)
 create mode 100644 tools/libs/vchan/vchan.h

diff --git a/tools/include/libxenvchan.h b/tools/include/libxenvchan.h
index d6010b145df2..30cc73cf97e3 100644
--- a/tools/include/libxenvchan.h
+++ b/tools/include/libxenvchan.h
@@ -86,6 +86,11 @@ struct libxenvchan {
 	int blocking:1;
 	/* communication rings */
 	struct libxenvchan_ring read, write;
+	/**
+	 * Base xenstore path for storing ring/event data used by the server
+	 * during cleanup.
+	 * */
+	char *xs_path;
 };
 
 /**
diff --git a/tools/libs/vchan/init.c b/tools/libs/vchan/init.c
index c8510e6ce98a..ae9a6b579753 100644
--- a/tools/libs/vchan/init.c
+++ b/tools/libs/vchan/init.c
@@ -46,6 +46,8 @@
 #include <xen/sys/gntdev.h>
 #include <libxenvchan.h>
 
+#include "vchan.h"
+
 #ifndef PAGE_SHIFT
 #define PAGE_SHIFT 12
 #endif
@@ -251,6 +253,12 @@ static int init_xs_srv(struct libxenvchan *ctrl, int domain, const char* xs_base
 	char ref[16];
 	char* domid_str = NULL;
 	xs_transaction_t xs_trans = XBT_NULL;
+
+	// store the base path so we can clean up on server closure
+	ctrl->xs_path = strdup(xs_base);
+	if (!ctrl->xs_path)
+		goto fail;
+
 	xs = xs_open(0);
 	if (!xs)
 		goto fail;
@@ -298,6 +306,23 @@ retry_transaction:
 	return ret;
 }
 
+void close_xs_srv(struct libxenvchan *ctrl)
+{
+	struct xs_handle *xs;
+
+	if (!ctrl->xs_path)
+		return;
+
+	xs = xs_open(0);
+	if (!xs)
+		goto fail;
+
+	xs_rm(xs, XBT_NULL, ctrl->xs_path);
+
+fail:
+	free(ctrl->xs_path);
+}
+
 static int min_order(size_t siz)
 {
 	int rv = PAGE_SHIFT;
diff --git a/tools/libs/vchan/io.c b/tools/libs/vchan/io.c
index da303fbc01ca..1f201ad554f2 100644
--- a/tools/libs/vchan/io.c
+++ b/tools/libs/vchan/io.c
@@ -40,6 +40,8 @@
 #include <xenctrl.h>
 #include <libxenvchan.h>
 
+#include "vchan.h"
+
 #ifndef PAGE_SHIFT
 #define PAGE_SHIFT 12
 #endif
@@ -384,5 +386,7 @@ void libxenvchan_close(struct libxenvchan *ctrl)
 		if (ctrl->gnttab)
 			xengnttab_close(ctrl->gnttab);
 	}
+	if (ctrl->is_server)
+		close_xs_srv(ctrl);
 	free(ctrl);
 }
diff --git a/tools/libs/vchan/vchan.h b/tools/libs/vchan/vchan.h
new file mode 100644
index 000000000000..621016ef42e5
--- /dev/null
+++ b/tools/libs/vchan/vchan.h
@@ -0,0 +1,31 @@
+/**
+ * @file
+ * @section AUTHORS
+ *
+ * Copyright (C) 2021 EPAM Systems Inc.
+ *
+ * @section LICENSE
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @section DESCRIPTION
+ *
+ *  This file contains common libxenvchan declarations.
+ */
+#ifndef LIBVCHAN_H
+#define LIBVCHAN_H
+
+void close_xs_srv(struct libxenvchan *ctrl);
+
+#endif /* LIBVCHAN_H */
-- 
2.25.1

On Wed, Feb 16, 2022 at 1:33 AM Oleksandr Andrushchenko
<andr2000@gmail.com> wrote:
>
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
> vchan server creates XenStore entries to advertise its event channel and
> ring, but those are not removed after the server quits.
> Add additional cleanup step, so those are removed, so clients do not try
> to connect to a non-existing server.
>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
> ---
> Since v1:
> - add NULL check after strdup
> ---
>  tools/include/libxenvchan.h |  5 +++++
>  tools/libs/vchan/init.c     | 25 +++++++++++++++++++++++++
>  tools/libs/vchan/io.c       |  4 ++++
>  tools/libs/vchan/vchan.h    | 31 +++++++++++++++++++++++++++++++
>  4 files changed, 65 insertions(+)
>  create mode 100644 tools/libs/vchan/vchan.h

> diff --git a/tools/libs/vchan/init.c b/tools/libs/vchan/init.c
> index c8510e6ce98a..ae9a6b579753 100644
> --- a/tools/libs/vchan/init.c
> +++ b/tools/libs/vchan/init.c
> @@ -46,6 +46,8 @@
>  #include <xen/sys/gntdev.h>
>  #include <libxenvchan.h>
>
> +#include "vchan.h"
> +
>  #ifndef PAGE_SHIFT
>  #define PAGE_SHIFT 12
>  #endif
> @@ -251,6 +253,12 @@ static int init_xs_srv(struct libxenvchan *ctrl, int domain, const char* xs_base
>         char ref[16];
>         char* domid_str = NULL;
>         xs_transaction_t xs_trans = XBT_NULL;
> +
> +       // store the base path so we can clean up on server closure
> +       ctrl->xs_path = strdup(xs_base);
> +       if (!ctrl->xs_path)
> +               goto fail;
> +
>         xs = xs_open(0);
>         if (!xs)
>                 goto fail;

Hi, Oleksandr,

You now have multiple conditions goto fail, so I think you need to add
the below snippet to avoid leaking memory.

if (ret) {
    free(ctrl->xs_path)
    ctrl->xs_path = NULL;
}

It's actually okay with your patch since libxenvchan_server_init() does:

        if (init_xs_srv(ctrl, domain, xs_path, ring_ref))
                goto out;
        return ctrl;
out:
        libxenvchan_close(ctrl);
        return 0;

and libxenvchan_close() will free xs_path.  But it's a little more
robust to cleanup local to the failure.

Thanks,
Jason

Hi Oleksandr,

On Wed, Feb 16, 2022 at 08:33:25AM +0200, Oleksandr Andrushchenko wrote:
> diff --git a/tools/libs/vchan/init.c b/tools/libs/vchan/init.c
> index c8510e6ce98a..ae9a6b579753 100644
> --- a/tools/libs/vchan/init.c
> +++ b/tools/libs/vchan/init.c
> @@ -251,6 +253,12 @@ static int init_xs_srv(struct libxenvchan *ctrl, int domain, const char* xs_base
>  	char ref[16];
>  	char* domid_str = NULL;
>  	xs_transaction_t xs_trans = XBT_NULL;
> +
> +	// store the base path so we can clean up on server closure
> +	ctrl->xs_path = strdup(xs_base);

You could do this in libxenvchan_server_init(), this might make it
easier to avoid leaking the path.

You need to initialise ctrl->xs_path in libxenvchan_server_init() in
any case before libxenvchan_close() is called.

I think you need to initialise ctrl->xs_path to NULL in
libxenvchan_client_init() as well even if it's not going to be used, to
avoid issue later in case the field start to be used.


> @@ -298,6 +306,23 @@ retry_transaction:
>  	return ret;
>  }
>  
> +void close_xs_srv(struct libxenvchan *ctrl)
> +{
> +	struct xs_handle *xs;
> +
> +	if (!ctrl->xs_path)
> +		return;
> +
> +	xs = xs_open(0);

There is missing a xs_close() call.

> +	if (!xs)
> +		goto fail;
> +
> +	xs_rm(xs, XBT_NULL, ctrl->xs_path);
> +
> +fail:
> +	free(ctrl->xs_path);
> +}
> +
>  static int min_order(size_t siz)
>  {
>  	int rv = PAGE_SHIFT;
> diff --git a/tools/libs/vchan/io.c b/tools/libs/vchan/io.c
> index da303fbc01ca..1f201ad554f2 100644
> --- a/tools/libs/vchan/io.c
> +++ b/tools/libs/vchan/io.c
> @@ -40,6 +40,8 @@
>  #include <xenctrl.h>
>  #include <libxenvchan.h>
>  
> +#include "vchan.h"
> +
>  #ifndef PAGE_SHIFT
>  #define PAGE_SHIFT 12
>  #endif
> @@ -384,5 +386,7 @@ void libxenvchan_close(struct libxenvchan *ctrl)
>  		if (ctrl->gnttab)
>  			xengnttab_close(ctrl->gnttab);
>  	}
> +	if (ctrl->is_server)
> +		close_xs_srv(ctrl);

Since init_xs_srv() is one of the last step of the initialisation of
*ctrl, I think close_xs_srv() should be one of the first step in
libxenvchan_close().

Thanks,

-- 
Anthony PERARD