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![Joao Martins](/assets/img/avatar_default.png)
Commitfd8aa9095a
("xen: optimize xenbus driver for multiple concurrent xenstore accesses") optimized xenbus concurrent accesses but in doing so broke UABI of /dev/xen/xenbus. Through /dev/xen/xenbus applications are in charge of xenbus message exchange with the correct header and body. Now, after the mentioned commit the replies received by application will no longer have the header req_id echoed back as it was on request (see specification below for reference), because that particular field is being overwritten by kernel. struct xsd_sockmsg { uint32_t type; /* XS_??? */ uint32_t req_id;/* Request identifier, echoed in daemon's response. */ uint32_t tx_id; /* Transaction id (0 if not related to a transaction). */ uint32_t len; /* Length of data following this. */ /* Generally followed by nul-terminated string(s). */ }; Before there was only one request at a time so req_id could simply be forwarded back and forth. To allow simultaneous requests we need a different req_id for each message thus kernel keeps a monotonic increasing counter for this field and is written on every request irrespective of userspace value. Forwarding again the req_id on userspace requests is not a solution because we would open the possibility of userspace-generated req_id colliding with kernel ones. So this patch instead takes another route which is to artificially keep user req_id while keeping the xenbus logic as is. We do that by saving the original req_id before xs_send(), use the private kernel counter as req_id and then once reply comes and was validated, we restore back the original req_id. Cc: <stable@vger.kernel.org> # 4.11 Fixes:fd8aa9095a
("xen: optimize xenbus driver for multiple concurrent xenstore accesses") Reported-by: Bhavesh Davda <bhavesh.davda@oracle.com> Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Reviewed-by: Juergen Gross <jgross@suse.com> Signed-off-by: Juergen Gross <jgross@suse.com>
136 lines
4.1 KiB
C
136 lines
4.1 KiB
C
/*
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* Private include for xenbus communications.
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*
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* Copyright (C) 2005 Rusty Russell, IBM Corporation
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* Copyright (C) 2005 XenSource Ltd.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License version 2
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* as published by the Free Software Foundation; or, when distributed
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* separately from the Linux kernel or incorporated into other
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* software packages, subject to the following license:
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this source file (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use, copy, modify,
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* merge, publish, distribute, sublicense, and/or sell copies of the Software,
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* and to permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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#ifndef _XENBUS_XENBUS_H
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#define _XENBUS_XENBUS_H
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#include <linux/mutex.h>
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#include <linux/uio.h>
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#include <xen/xenbus.h>
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#define XEN_BUS_ID_SIZE 20
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struct xen_bus_type {
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char *root;
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unsigned int levels;
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int (*get_bus_id)(char bus_id[XEN_BUS_ID_SIZE], const char *nodename);
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int (*probe)(struct xen_bus_type *bus, const char *type,
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const char *dir);
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void (*otherend_changed)(struct xenbus_watch *watch, const char *path,
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const char *token);
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struct bus_type bus;
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};
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enum xenstore_init {
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XS_UNKNOWN,
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XS_PV,
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XS_HVM,
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XS_LOCAL,
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};
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struct xs_watch_event {
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struct list_head list;
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unsigned int len;
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struct xenbus_watch *handle;
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const char *path;
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const char *token;
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char body[];
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};
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enum xb_req_state {
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xb_req_state_queued,
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xb_req_state_wait_reply,
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xb_req_state_got_reply,
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xb_req_state_aborted
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};
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struct xb_req_data {
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struct list_head list;
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wait_queue_head_t wq;
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struct xsd_sockmsg msg;
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uint32_t caller_req_id;
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enum xsd_sockmsg_type type;
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char *body;
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const struct kvec *vec;
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int num_vecs;
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int err;
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enum xb_req_state state;
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void (*cb)(struct xb_req_data *);
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void *par;
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};
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extern enum xenstore_init xen_store_domain_type;
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extern const struct attribute_group *xenbus_dev_groups[];
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extern struct mutex xs_response_mutex;
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extern struct list_head xs_reply_list;
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extern struct list_head xb_write_list;
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extern wait_queue_head_t xb_waitq;
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extern struct mutex xb_write_mutex;
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int xs_init(void);
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int xb_init_comms(void);
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void xb_deinit_comms(void);
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int xs_watch_msg(struct xs_watch_event *event);
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void xs_request_exit(struct xb_req_data *req);
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int xenbus_match(struct device *_dev, struct device_driver *_drv);
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int xenbus_dev_probe(struct device *_dev);
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int xenbus_dev_remove(struct device *_dev);
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int xenbus_register_driver_common(struct xenbus_driver *drv,
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struct xen_bus_type *bus,
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struct module *owner,
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const char *mod_name);
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int xenbus_probe_node(struct xen_bus_type *bus,
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const char *type,
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const char *nodename);
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int xenbus_probe_devices(struct xen_bus_type *bus);
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void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);
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void xenbus_dev_shutdown(struct device *_dev);
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int xenbus_dev_suspend(struct device *dev);
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int xenbus_dev_resume(struct device *dev);
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int xenbus_dev_cancel(struct device *dev);
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void xenbus_otherend_changed(struct xenbus_watch *watch,
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const char *path, const char *token,
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int ignore_on_shutdown);
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int xenbus_read_otherend_details(struct xenbus_device *xendev,
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char *id_node, char *path_node);
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void xenbus_ring_ops_init(void);
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int xenbus_dev_request_and_reply(struct xsd_sockmsg *msg, void *par);
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void xenbus_dev_queue_reply(struct xb_req_data *req);
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#endif
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