Re: [Xen-devel] [v3 2/5] Qemu-Xen-vTPM: Xen frontend driver infrastructure

["Xu, Quan" <quan.xu@xxxxxxxxx>]

> -----Original Message-----
> From: Stefano Stabellini [mailto:stefano.stabellini@xxxxxxxxxxxxx]
> Sent: Tuesday, January 20, 2015 1:15 AM
> To: Xu, Quan
> Cc: qemu-devel@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxx;
> stefano.stabellini@xxxxxxxxxxxxx
> Subject: Re: [v3 2/5] Qemu-Xen-vTPM: Xen frontend driver infrastructure
> 
> On Tue, 30 Dec 2014, Quan Xu wrote:
> > This patch adds infrastructure for xen front drivers living in qemu,
> > so drivers don't need to implement common stuff on their own.  It's
> > mostly xenbus management stuff: some functions to access XenStore,
> > setting up XenStore watches, callbacks on device discovery and state
> > changes, and handle event channel between the virtual machines.
> >
> > Call xen_fe_register() function to register XenDevOps, and make sure,
> > XenDevOps's flags is DEVOPS_FLAG_FE, which is flag bit to point out
> > the XenDevOps is Xen frontend.
> >
> > --Changes in v3:
> > -New xen_frontend.c file
> > -Move xenbus_switch_state() to xen_frontend.c -Move xen_stubdom_be()
> > to xenstore_fe_read_be_str() -Move *_stubdom_*() to *_fe_*()
> >
> > Signed-off-by: Quan Xu <quan.xu@xxxxxxxxx>
> > ---
> >  hw/xen/Makefile.objs         |   2 +-
> >  hw/xen/xen_backend.c         |  11 +-
> >  hw/xen/xen_frontend.c        | 323
> +++++++++++++++++++++++++++++++++++++++++++
> >  include/hw/xen/xen_backend.h |  14 ++
> >  4 files changed, 348 insertions(+), 2 deletions(-)  create mode
> > 100644 hw/xen/xen_frontend.c
> >
> > diff --git a/hw/xen/Makefile.objs b/hw/xen/Makefile.objs index
> > a0ca0aa..b0bb065 100644
> > --- a/hw/xen/Makefile.objs
> > +++ b/hw/xen/Makefile.objs
> > @@ -1,5 +1,5 @@
> >  # xen backend driver support
> > -common-obj-$(CONFIG_XEN_BACKEND) += xen_backend.o xen_devconfig.o
> > +common-obj-$(CONFIG_XEN_BACKEND) += xen_backend.o xen_devconfig.o
> > +xen_frontend.o
> >
> >  obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen-host-pci-device.o
> >  obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen_pt.o xen_pt_config_init.o
> > xen_pt_msi.o diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
> > index b2cb22b..ad6e324 100644
> > --- a/hw/xen/xen_backend.c
> > +++ b/hw/xen/xen_backend.c
> > @@ -275,7 +275,7 @@ static struct XenDevice *xen_be_get_xendev(const
> > char *type, int dom, int dev,
> >  /*
> >   * release xen backend device.
> >   */
> > -static struct XenDevice *xen_be_del_xendev(int dom, int dev)
> > +struct XenDevice *xen_be_del_xendev(int dom, int dev)
> >  {
> >      struct XenDevice *xendev, *xnext;
> >
> > @@ -681,6 +681,10 @@ static void xenstore_update(void *unused)
> >      if (sscanf(vec[XS_WATCH_TOKEN], "fe:%" PRIxPTR, &ptr) == 1) {
> >          xenstore_update_fe(vec[XS_WATCH_PATH], (void*)ptr);
> >      }
> > +    if (sscanf(vec[XS_WATCH_TOKEN], "stub:%" PRIxPTR ":%d:%" PRIxPTR,
> > +               &type, &dom, &ops) == 3) {
> > +        xenstore_fe_update(vec[XS_WATCH_PATH], (void *)type, dom,
> (void *)ops);
> > +    }
> 
> Why "stub:"? Where is it coming from?
'stub:' is a head of token for xs_watch. The better head is 'fe:', but it is 
used by backend.
So I call it 'stub:', which refers to 'Xen stubdomain backend'. 
'stub:' is initialized in xenstore_fe_scan().


> 
> I think that the xenstore_update function should be moved to a new file:
> we don't want xen_backend.c to be handling any frontend updates.
> Maybe you could create a new file, hw/xen/xen_pvdev.c?
> 

Make sense. 

> 
> >  cleanup:
> >      free(vec);
> > @@ -808,3 +812,8 @@ void xen_be_printf(struct XenDevice *xendev, int
> msg_level, const char *fmt, ...
> >      }
> >      qemu_log_flush();
> >  }
> > +
> > +void xen_qtail_insert_xendev(struct XenDevice *xendev) {
> > +    QTAILQ_INSERT_TAIL(&xendevs, xendev, next); }
> 
> You should either move the xendevs queue to the new file xen_pvdev.c or you
> should introduce a separate xendevs queue for frontends in xen_frontend.c.
> 
> 
> > diff --git a/hw/xen/xen_frontend.c b/hw/xen/xen_frontend.c new file
> > mode 100644 index 0000000..07ffc5c
> > --- /dev/null
> > +++ b/hw/xen/xen_frontend.c
> > @@ -0,0 +1,323 @@
> > +/*
> > + * Xen frontend driver infrastructure
> > + *
> > + *  Copyright (c) 2014 Intel Corporation
> > + *  Authors:
> > + *    Quan Xu <quan.xu@xxxxxxxxx>
> > + *
> > + * 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 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/>  */
> > +
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <stdarg.h>
> > +#include <string.h>
> > +#include <unistd.h>
> > +#include <fcntl.h>
> > +#include <inttypes.h>
> > +#include <sys/types.h>
> > +#include <sys/stat.h>
> > +#include <sys/mman.h>
> > +#include <sys/signal.h>
> > +
> > +#include "hw/hw.h"
> > +#include "sysemu/char.h"
> > +#include "qemu/log.h"
> > +#include "hw/xen/xen_backend.h"
> > +#include <xen/grant_table.h>
> > +
> > +/* private */
> > +static int debug;
> > +
> > +/* ------------------------------------------------------------- */
> > +/*Get backend with fe type|domid, try to write the backend-id when
> > +*create virtual machine.
> > + *
> > + *[XenStore]
> > + *
> > + *Dom.ID = ""
> > + *  device
> > + *    vtpm = ""
> > + *      0 = ""
> > + *        backend-id = "ID"
> > + *[..]
> > + */
> > +
> > +char *xenstore_fe_read_be_str(const char *type, int dom, int dev) {
> > +    char *val, *domu;
> > +    char path[XEN_BUFSIZE];
> > +    unsigned int len, ival;
> > +
> > +    /*fe path*/
> > +    domu = xs_get_domain_path(xenstore, dom);
> > +    snprintf(path, sizeof(path), "%s/device/%s/%d/backend-id",
> > +             domu, type, dev);
> > +    g_free(domu);
> > +
> > +    val = xs_read(xenstore, 0, path, &len);
> > +    if (!val || 1 != sscanf(val, "%d", &ival)) {
> > +        g_free(val);
> > +        return NULL;
> > +    }
> > +    g_free(val);
> > +
> > +    /*be path*/
> > +    domu = xs_get_domain_path(xenstore, ival);
> > +
> > +    return domu;
> > +}
> > +
> > +/*make sure, initialize the 'xendev->fe' in xendev->ops->init() or
> > + * xendev->ops->initialize()
> > + */
> > +int xenbus_switch_state(struct XenDevice *xendev, enum xenbus_state
> > +xbus) {
> > +    xs_transaction_t xbt = XBT_NULL;
> > +
> > +    if (xendev->fe_state == xbus) {
> > +        return 0;
> > +    }
> > +
> > +    xendev->fe_state = xbus;
> > +    if (xendev->fe == NULL) {
> > +        xen_be_printf(NULL, 0, "xendev->fe is NULL\n");
> > +        return -1;
> > +    }
> > +
> > +retry_transaction:
> > +    xbt = xs_transaction_start(xenstore);
> > +    if (xbt == XBT_NULL) {
> > +        goto abort_transaction;
> > +    }
> > +
> > +    if (xenstore_write_int(xendev->fe, "state", xbus)) {
> > +        goto abort_transaction;
> > +    }
> > +
> > +    if (!xs_transaction_end(xenstore, xbt, 0)) {
> > +        if (errno == EAGAIN) {
> > +            goto retry_transaction;
> > +        }
> > +    }
> > +
> > +    return 0;
> > +
> > +abort_transaction:
> > +    xs_transaction_end(xenstore, xbt, 1);
> > +    return -1;
> > +}
> > +
> > +void xenstore_fe_update(char *watch, char *type, int dom, struct
> > +XenDevOps *ops) {
> > +    struct XenDevice *xendev;
> > +    char path[XEN_BUFSIZE];
> > +    char *ptr, *bepath;
> > +    unsigned int len, dev;
> > +
> > +    if (!(ops->flags & DEVOPS_FLAG_FE)) {
> > +        return;
> > +    }
> > +
> > +    len = snprintf(path, sizeof(path), "backend/%s/%d", type, dom);
> > +    ptr = strstr(watch, path);
> > +    if (ptr == NULL) {
> > +        return;
> > +    }
> > +
> > +    if (sscanf(ptr+len, "/%u/%255s", &dev, path) != 2) {
> > +        strcpy(path, "");
> > +        if (sscanf(ptr+len, "/%u", &dev) != 1) {
> > +            dev = -1;
> > +        }
> > +    }
> > +
> > +    if (dev == -1) {
> > +        return;
> > +    }
> > +
> > +    xendev = xen_fe_get_xendev(type, dom, dev, ops);
> > +    if (xendev != NULL) {
> > +        bepath = xs_read(xenstore, 0, xendev->be, &len);
> > +        /*bepath is NULL, indicates that the backend is not running,
> > +         *delete it.
> > +         */
> > +        if (bepath == NULL) {
> > +            xen_be_del_xendev(dom, dev);
> > +        } else {
> > +            free(bepath);
> > +            if (xendev->ops->backend_changed) {
> > +                xendev->ops->backend_changed(xendev, path);
> > +            }
> > +        }
> > +    }
> > +}
> > +
> > +/*
> > + * get xen fe device, allocate a new one if it doesn't exist.
> > + */
> > +struct XenDevice *xen_fe_get_xendev(const char *type, int dom, int dev,
> > +                                    struct XenDevOps *ops) {
> > +    struct XenDevice *xendev;
> > +    char *stub;
> > +
> > +    xendev = xen_be_find_xendev(type, dom, dev);
> > +    if (xendev) {
> > +        return xendev;
> > +    }
> > +
> > +    /* init new xendev */
> > +    xendev = g_malloc0(ops->size);
> > +    xendev->type  = type;
> > +    xendev->dom   = dom;
> > +    xendev->dev   = dev;
> > +    xendev->ops   = ops;
> > +
> > +    /*return if the ops->flags is not DEVOPS_FLAG_FE*/
> > +    if (!(ops->flags & DEVOPS_FLAG_FE)) {
> > +        return NULL;
> > +    }
> > +
> > +    stub = xenstore_fe_read_be_str(xendev->type, xendev->dom,
> xendev->dev);
> > +    snprintf(xendev->be, sizeof(xendev->be), "%s/backend/%s/%d/%d",
> > +             stub, xendev->type, xendev->dom, xendev->dev);
> > +    g_free(stub);
> > +    snprintf(xendev->name, sizeof(xendev->name), "%s-%d",
> > +             xendev->type, xendev->dev);
> > +
> > +    xendev->debug = debug;
> > +    xendev->local_port = -1;
> > +
> > +    xendev->evtchndev = xen_xc_evtchn_open(NULL, 0);
> > +    if (xendev->evtchndev == XC_HANDLER_INITIAL_VALUE) {
> > +        xen_be_printf(NULL, 0, "can't open evtchn device\n");
> > +        g_free(xendev);
> > +        return NULL;
> > +    }
> > +    fcntl(xc_evtchn_fd(xendev->evtchndev), F_SETFD, FD_CLOEXEC);
> > +
> > +    if (ops->flags & DEVOPS_FLAG_NEED_GNTDEV) {
> > +        xendev->gnttabdev = xen_xc_gnttab_open(NULL, 0);
> > +        if (xendev->gnttabdev == XC_HANDLER_INITIAL_VALUE) {
> > +            xen_be_printf(NULL, 0, "can't open gnttab device\n");
> > +            xc_evtchn_close(xendev->evtchndev);
> > +            g_free(xendev);
> > +            return NULL;
> > +        }
> > +    } else {
> > +        xendev->gnttabdev = XC_HANDLER_INITIAL_VALUE;
> > +    }
> > +
> > +    xen_qtail_insert_xendev(xendev);
> > +
> > +    if (xendev->ops->alloc) {
> > +        xendev->ops->alloc(xendev);
> > +    }
> > +
> > +    return xendev;
> > +}
> > +
> > +/* simplify QEMU side, a thread is running in Xen backend, which will
> > + * connect frontend when the frontend is initialised. Call these
> > +initialised
> > + * functions.
> > + */
> > +
> > +static int xen_fe_check(struct XenDevice *xendev, uint32_t domid,
> > +                        int handle)
> > +{
> > +    int rc = 0;
> > +
> > +    if (xendev->ops->init) {
> > +        rc = xendev->ops->init(xendev);
> > +    }
> > +
> > +    if (rc != 0) {
> > +        xen_be_printf(xendev, 0, "xendev %s init error\n",
> > +                      xendev->name);
> > +       goto err;
> > +    }
> > +
> > +    if (xendev->ops->initialise) {
> > +        rc = xendev->ops->initialise(xendev);
> > +    }
> > +
> > +    if (rc != 0) {
> > +        xen_be_printf(xendev, 0, "xendev %s initialise error\n",
> > +                      xendev->name);
> > +       goto err;
> > +    }
> 
> Shouldn't you be checking the backend status before setting the frontend to
> connected?  Something like xen_be_try_connected?
> 

Yes, I will do it in v4.

-Quan

> 
> > +    if (xendev->ops->connected) {
> > +        xendev->ops->connected(xendev);
> > +    }
> > +
> > +    return rc;
> > +
> > +err:
> > +    xen_be_del_xendev(domid, handle);
> > +    return -1;
> > +}
> > +
> > +static int xenstore_fe_scan(const char *type, uint32_t domid,
> > +                            struct XenDevOps *ops) {
> > +    struct XenDevice *xendev;
> > +    char path[XEN_BUFSIZE], token[XEN_BUFSIZE];
> > +    char *domu;
> > +    unsigned int cdev, j;
> > +    char **dev = NULL;
> > +
> > +    /*Xen frontend : /local/domain/ID */
> > +    domu = xs_get_domain_path(xenstore, domid);
> > +    snprintf(path, sizeof(path), "%s/device/%s",
> > +             domu, type);
> > +    free(domu);
> > +    dev = xs_directory(xenstore, 0, path, &cdev);
> > +    if (dev == NULL) {
> > +        return 0;
> > +    }
> > +
> > +    for (j = 0; j < cdev; j++) {
> > +        xendev = xen_fe_get_xendev(type, domid, atoi(dev[j]), ops);
> > +        if (xendev == NULL) {
> > +            xen_be_printf(xendev, 0, "xendev is NULL.\n");
> > +            continue;
> > +        }
> > +
> > +        /* simplify QEMU side, a thread is running in Xen backend, which 
> > will
> > +         * connect frontend when the frontend is initialised.
> > +         */
> > +        if (xen_fe_check(xendev, domid, atoi(dev[j])) < 0) {
> > +            xen_be_printf(xendev, 0, "xendev fe_check error.\n");
> > +            continue;
> > +        }
> > +
> > +        /*setup watch*/
> > +        snprintf(token, sizeof(token), "stub:%p:%d:%p",
> > +                 type, domid, xendev->ops);
> > +        if (!xs_watch(xenstore, xendev->be, token)) {
> > +            xen_be_printf(xendev, 0, "xs_watch failed.\n");
> > +            continue;
> > +        }
> > +    }
> > +
> > +    free(dev);
> > +    return 0;
> > +}
> > +
> > +int xen_fe_register(const char *type, struct XenDevOps *ops) {
> > +    return xenstore_fe_scan(type, xen_domid, ops); }
> > diff --git a/include/hw/xen/xen_backend.h
> > b/include/hw/xen/xen_backend.h index 3b4125e..06e202f 100644
> > --- a/include/hw/xen/xen_backend.h
> > +++ b/include/hw/xen/xen_backend.h
> > @@ -15,6 +15,8 @@ struct XenDevice;
> >  #define DEVOPS_FLAG_NEED_GNTDEV   1
> >  /* don't expect frontend doing correct state transitions (aka console
> > quirk) */  #define DEVOPS_FLAG_IGNORE_STATE  2
> > +/*dev is frontend device*/
> > +#define DEVOPS_FLAG_FE            4
> >
> >  struct XenDevOps {
> >      size_t    size;
> > @@ -80,6 +82,8 @@ int xenstore_read_fe_uint64(struct XenDevice
> > *xendev, const char *node, uint64_t  const char *xenbus_strstate(enum
> > xenbus_state state);  struct XenDevice *xen_be_find_xendev(const char
> > *type, int dom, int dev);  void xen_be_check_state(struct XenDevice
> > *xendev);
> > +struct XenDevice *xen_be_del_xendev(int dom, int dev); void
> > +xen_qtail_insert_xendev(struct XenDevice *xendev);
> >
> >  /* xen backend driver bits */
> >  int xen_be_init(void);
> > @@ -91,6 +95,16 @@ int xen_be_send_notify(struct XenDevice *xendev);
> > void xen_be_printf(struct XenDevice *xendev, int msg_level, const char
> *fmt, ...)
> >      GCC_FMT_ATTR(3, 4);
> >
> > +/*Xen frontend driver*/
> > +int xen_fe_register(const char *type, struct XenDevOps *ops); int
> > +xen_be_alloc_unbound(struct XenDevice *xendev, int dom, int
> > +remote_dom); char *xenstore_fe_read_be_str(const char *type, int dom,
> > +int dev); int xenbus_switch_state(struct XenDevice *xendev, enum
> > +xenbus_state xbus); struct XenDevice *xen_fe_get_xendev(const char *type,
> int dom, int dev,
> > +                                    struct XenDevOps *ops); void
> > +xenstore_fe_update(char *watch, char *type, int dom,
> > +                        struct XenDevOps *ops);
> > +
> >  /* actual backend drivers */
> >  extern struct XenDevOps xen_console_ops;      /* xen_console.c     */
> >  extern struct XenDevOps xen_kbdmouse_ops;     /* xen_framebuffer.c */
> > --
> > 1.8.3.2
> >

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