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Message-ID: <9dc05fb2-cb84-d8e7-848b-37fb9c86b782@oracle.com>
Date: Thu, 22 Dec 2016 10:49:21 -0500
From: Boris Ostrovsky <boris.ostrovsky@...cle.com>
To: Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 2/3] xen: return xenstore command failures via response
instead of rc
On 12/22/2016 02:19 AM, Juergen Gross wrote:
> When the xenbus driver does some special handling for a Xenstore
> command any error condition related to the command should be returned
> via an error response instead of letting the related write operation
> fail. Otherwise the user land handler might take wrong decisions
> assuming the connection to Xenstore is broken.
Do we expect the user to always read the reply if no error code was
returned?
-boris
>
> While at it try to return the same error values xenstored would
> return for those cases.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
> drivers/xen/xenbus/xenbus_dev_frontend.c | 47 ++++++++++++++++++--------------
> 1 file changed, 27 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
> index a068281..79130b3 100644
> --- a/drivers/xen/xenbus/xenbus_dev_frontend.c
> +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
> @@ -302,6 +302,29 @@ static void watch_fired(struct xenbus_watch *watch,
> mutex_unlock(&adap->dev_data->reply_mutex);
> }
>
> +static int xenbus_command_reply(struct xenbus_file_priv *u,
> + unsigned int msg_type, const char *reply)
> +{
> + struct {
> + struct xsd_sockmsg hdr;
> + const char body[16];
> + } msg;
> + int rc;
> +
> + msg.hdr = u->u.msg;
> + msg.hdr.type = msg_type;
> + msg.hdr.len = strlen(reply) + 1;
> + if (msg.hdr.len > sizeof(msg.body))
> + return -E2BIG;
> +
> + mutex_lock(&u->reply_mutex);
> + rc = queue_reply(&u->read_buffers, &msg, sizeof(msg.hdr) + msg.hdr.len);
> + wake_up(&u->read_waitq);
> + mutex_unlock(&u->reply_mutex);
> +
> + return rc;
> +}
> +
> static int xenbus_write_transaction(unsigned msg_type,
> struct xenbus_file_priv *u)
> {
> @@ -321,7 +344,7 @@ static int xenbus_write_transaction(unsigned msg_type,
> if (trans->handle.id == u->u.msg.tx_id)
> break;
> if (&trans->list == &u->transactions)
> - return -ESRCH;
> + return xenbus_command_reply(u, XS_ERROR, "ENOENT");
> }
>
> reply = xenbus_dev_request_and_reply(&u->u.msg);
> @@ -372,12 +395,12 @@ static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u)
> path = u->u.buffer + sizeof(u->u.msg);
> token = memchr(path, 0, u->u.msg.len);
> if (token == NULL) {
> - rc = -EILSEQ;
> + rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
> goto out;
> }
> token++;
> if (memchr(token, 0, u->u.msg.len - (token - path)) == NULL) {
> - rc = -EILSEQ;
> + rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
> goto out;
> }
>
> @@ -411,23 +434,7 @@ static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u)
> }
>
> /* Success. Synthesize a reply to say all is OK. */
> - {
> - struct {
> - struct xsd_sockmsg hdr;
> - char body[3];
> - } __packed reply = {
> - {
> - .type = msg_type,
> - .len = sizeof(reply.body)
> - },
> - "OK"
> - };
> -
> - mutex_lock(&u->reply_mutex);
> - rc = queue_reply(&u->read_buffers, &reply, sizeof(reply));
> - wake_up(&u->read_waitq);
> - mutex_unlock(&u->reply_mutex);
> - }
> + rc = xenbus_command_reply(u, msg_type, "OK");
>
> out:
> return rc;
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