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Re: [libvirt] [PATCH 1/5] Add pci utility functions



On Tue, Feb 24, 2009 at 10:21:47PM +0000, Mark McLoughlin wrote:
> Add implementations of dettach, reattach and reset for
> PCI devices.
> 
> Background to this code can be found here:
> 
>   http://marc.info/?l=kvm&m=123454366317045
> 
> Some notes:
> 
>   * pci-stub was first introduced in 2.6.29; if it's
>     not available, then dettach can only unbind the
>     device from the host driver
> 
>   * remove_id is queued up for 2.6.30; in it's absence
>     reattach cannot re-bind the device to the original
>     driver
> 
>   * If the device supports Function Level Reset, we
>     just don't bother doing the reset - KVM will do
>     this before and after a guest runs
> 
>   * Currently, if a reset would affect another device
>     on the same bus, or another function on the same
>     multi-function device, then we just refuse to do
>     the reset. In future, we could allow the reset
>     as long as it doesn't affect a device in use by
>     the host or assigned to another guest
> 
>   * The device reset code is similar in concept to
>     some of Xen's code
> 
> Signed-off-by: Mark McLoughlin <markmc redhat com>

I can't claim to understand all the gory PCI code in here,
but a few API level suggestions.

Also, would it be worth (or possible) using libpciaccess.so
for this instead of poking Linux sysfs files directly ?

> +static int
> +pciRead(pciDevice *dev, unsigned pos, uint8_t *buf, unsigned buflen)
> +{
> +    memset(buf, 0, buflen);
> +
> +    if (pciOpenConfig(dev) < 0)
> +        return -1;
> +
> +    if (pread(dev->fd, buf, buflen, pos) < 0) {
> +        char ebuf[1024];
> +        VIR_WARN(_("Failed to read from '%s' : %s"), dev->path,
> +                 virStrerror(errno, ebuf, sizeof(ebuf)));
> +        return -1;
> +    }
> +    return 0;
> +}

I think this needs to check for a possible short read too.
Perhaps better off doing a seek and then saferead(), or
defining a safepread() function.

> +static int
> +pciWrite(pciDevice *dev, unsigned pos, uint8_t *buf, unsigned buflen)
> +{
> +    if (pciOpenConfig(dev) < 0)
> +        return -1;
> +
> +    if (pwrite(dev->fd, buf, buflen, pos) < 0) {
> +        char ebuf[1024];
> +        VIR_WARN(_("Failed to write to '%s' : %s"), dev->path,
> +                 virStrerror(errno, ebuf, sizeof(ebuf)));
> +        return -1;
> +    }
> +    return 0;
> +}

Likewise here needs to validate actual num of bytes written

> +int
> +pciDettachDevice(pciDevice *dev)
> +{
> +    char path[PATH_MAX];
> +
> +    /* Try loading the pci-stub module if it isn't already loaded;
> +     * return an error if there is no pci-stub available.
> +     */
> +    if (!virFileExists(PCI_SYSFS "drivers/pci-stub")) {
> +        const char *const modprobeargv[] = { MODPROBE, "pci-stub", NULL };
> +
> +        if (virRun(dev->conn, modprobeargv, NULL) < 0) {
> +            char ebuf[1024];
> +            VIR_WARN(_("modprobe pci-stub failed: %s"),
> +                     virStrerror(errno, ebuf, sizeof ebuf));
> +        }
> +    }
> +
> +    if (!virFileExists(PCI_SYSFS "drivers/pci-stub")) {
> +        VIR_WARN(_("pci-stub driver not available, cannot bind device %s to it"),
> +                 dev->name);
> +    } else {
> +        /* Add the PCI device ID to pci-stub's dynamic ID table;
> +         * this is needed to allow us to bind the device to pci-stub.
> +         * Note: if the device is not currently bound to any driver,
> +         * pci-stub will immediately be bound to the device. Also, note
> +         * that if a new device with this ID is hotplugged, or if a probe
> +         * is triggered for such a device, it will also be immediately
> +         * bound by pci-stub.
> +         */
> +        if (virFileWriteStr(PCI_SYSFS "drivers/pci-stub/new_id", dev->id) < 0) {
> +            virReportSystemError(dev->conn, errno,
> +                                 _("Failed to add PCI device ID '%s' to pci-stub/new_id"),
> +                                 dev->id);
> +            return -1;
> +        }
> +    }
> +
> +    /* If the device is already bound to a driver, unbind it.
> +     * Note, this will have rather unpleasant side effects if this
> +     * PCI device happens to be IDE controller for the disk hosting
> +     * your root filesystem.
> +     */
> +    snprintf(path, sizeof(path),
> +             PCI_SYSFS "devices/%s/driver/unbind", dev->name);
> +    if (virFileExists(path) && virFileWriteStr(path, dev->name) < 0) {
> +        virReportSystemError(dev->conn, errno,
> +                             _("Failed to unbind PCI device '%s'"), dev->name);
> +        return -1;
> +    }
> +
> +    if (virFileExists(PCI_SYSFS "drivers/pci-stub")) {
> +        /* If the device isn't already bound to pci-stub, try binding it now.
> +         */
> +        snprintf(path, sizeof(path), PCI_SYSFS "devices/%s/driver", dev->name);
> +        if (!virFileLinkPointsTo(path, PCI_SYSFS "drivers/pci-stub") &&
> +            virFileWriteStr(PCI_SYSFS "drivers/pci-stub/bind", dev->name) < 0) {
> +            virReportSystemError(dev->conn, errno,
> +                                 _("Failed to bind PCI device '%s' to pci-stub"),
> +                                 dev->name);
> +            return -1;
> +        }
> +
> +        /* If 'remove_id' exists, remove the device id from pci-stub's dynamic
> +         * ID table so that 'drivers_probe' works below.
> +         */
> +        if (virFileExists(PCI_SYSFS "drivers/pci-stub/remove_id") &&
> +            virFileWriteStr(PCI_SYSFS "drivers/pci-stub/remove_id", dev->id) < 0) {
> +            virReportSystemError(dev->conn, errno,
> +                                 _("Failed to remove PCI ID '%s' with pci-stub/remove_id"),
> +                                 dev->id);
> +            return -1;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +int
> +pciReAttachDevice(pciDevice *dev)
> +{
> +    if (virFileExists(PCI_SYSFS "drivers/pci-stub")) {
> +        char path[PATH_MAX];
> +
> +        /* If the device is bound to pci-stub, unbind it.
> +         */
> +        snprintf(path, sizeof(path), PCI_SYSFS "devices/%s/driver", dev->name);
> +        if (virFileLinkPointsTo(path, PCI_SYSFS "drivers/pci-stub") &&
> +            virFileWriteStr(PCI_SYSFS "drivers/pci-stub/unbind", dev->name) < 0) {
> +            virReportSystemError(dev->conn, errno,
> +                                 _("Failed to bind PCI device '%s' to pci-stub"),
> +                                 dev->name);
> +            return -1;
> +        }
> +    }
> +
> +    /* Trigger a re-probe of the device is not in pci-stub's dynamic
> +     * ID table. If pci-stub is available, but 'remove_id' isn't
> +     * available, then re-probing would just cause the device to be
> +     * re-bound to pci-stub.
> +     */
> +    if (!virFileExists(PCI_SYSFS "drivers/pci-stub") ||
> +        virFileExists(PCI_SYSFS "drivers/pci-stub/remove_id")) {
> +        if (virFileWriteStr(PCI_SYSFS "drivers_probe", dev->name) < 0) {
> +            virReportSystemError(dev->conn, errno,
> +                                 _("Failed to trigger a re-probe for PCI device '%s'"),
> +                                 dev->name);
> +            return -1;
> +        }
> +    }
> +
> +    return 0;
> +}

These functions really need to take the driver name as an argument,
so we can pass 'pci-stub' for KVM (or modern pv_ops Xen dom0), or
'pciback' for old pre-pv_ops Xen dom0.

> +pciDevice *pciGetDevice      (virConnectPtr  conn,
> +                              unsigned       vendor,
> +                              unsigned       product,
> +                              unsigned       domain,
> +                              unsigned       bus,
> +                              unsigned       slot,
> +                              unsigned       function);
> +void       pciFreeDevice     (pciDevice     *dev);
> +int        pciDettachDevice  (pciDevice     *dev);
> +int        pciReAttachDevice (pciDevice     *dev);
> +int        pciResetDevice    (pciDevice     *dev);

I prefer it to pass the virConnectPtr conn into each of
these calls rather than storing it in the pciDevice
struct. It'd also be good to remove the vendor/product
ID here, and have this code lookup them up from te address
info, since the domain XML format only provides the caller
with the domain/bus/slot/function address info.

Daniel
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