[libvirt] [PATCH v1 05/31] virpcimock: Create driver_override file in device dirs

[Michal Privoznik]

On 7/16/19 2:13 PM, Peter Krempa wrote:
> On Thu, Jul 11, 2019 at 17:53:52 +0200, Michal Privoznik wrote:
>> Newer kernels (v3.16-rc1~29^2~6^4) have 'driver_override' file
>> which simplifies way of binding a PCI device to desired driver.
>> Libvirt has support for this for some time too (v2.3.0-rc1~236),
>> but not our virpcimock. So far we did not care because our code
>> is designed to deal with this situation. Except for one.
>> hypothetical case: binding a device to the vfio-pci driver can be
>> successful only via driver_override. Any attempt to bind a PCI
>> device to vfio-pci driver using old method (new_id + unbind +
>> bind) will fail because of b803b29c1a5. While on vanilla kernel
> 
> You've reverted the mentioned commit just before this patch.

Yep, I needed to do that s

> 
> Also I did not understand what this is supposed to do from the commit
> message. Perhaps due to my limited understanding of the pci detachment
> code. So either somebody else reviews this or you'll need to reprhase
> the commit message.
> 
>> I'm able to use the old method successfully, it's failing on RHEL
>> kernels (not sure why).
> 
> This does not inspire confidence.

I've asked Alex Williamson about this and he confirmed that he can see 
this behaviour but nor he could understand why RHEL-7 kernel behaves 
that way.

> 
>>
>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>> ---
>>   tests/virpcimock.c | 57 +++++++++++++++++++++++++++++++++++++++++-----
>>   1 file changed, 51 insertions(+), 6 deletions(-)
>>
>> diff --git a/tests/virpcimock.c b/tests/virpcimock.c
>> index 6865f992dc..18d06d11d4 100644
>> --- a/tests/virpcimock.c
>> +++ b/tests/virpcimock.c
>> @@ -87,6 +87,11 @@ char *fakesysfspcidir;
>>    *   Probe for a driver that handles the specified device.
>>    *   Data in format "DDDD:BB:DD.F" (Domain:Bus:Device.Function).
>>    *
>> + * /sys/bus/pci/devices/<device>/driver_override
>> + *   Name of a driver that overrides preferred driver can be written
>> + *   here. The device will be attached to it on drivers_probe event.
>> + *   Writing an empty string (or "\n") clears the override.
>> + *
>>    * As a little hack, we are not mocking write to these files, but close()
>>    * instead. The advantage is we don't need any self growing array to hold the
>>    * partial writes and construct them back. We can let all the writes finish,
>> @@ -147,6 +152,7 @@ static struct pciDevice *pci_device_find_by_content(const char *path);
>>   static void pci_driver_new(const char *name, int fail, ...);
>>   static struct pciDriver *pci_driver_find_by_dev(struct pciDevice *dev);
>>   static struct pciDriver *pci_driver_find_by_path(const char *path);
>> +static struct pciDriver *pci_driver_find_by_driver_override(struct pciDevice *dev);
>>   static int pci_driver_bind(struct pciDriver *driver, struct pciDevice *dev);
>>   static int pci_driver_unbind(struct pciDriver *driver, struct pciDevice *dev);
>>   static int pci_driver_handle_change(int fd, const char *path);
>> @@ -202,7 +208,8 @@ make_symlink(const char *path,
>>   static int
>>   pci_read_file(const char *path,
>>                 char *buf,
>> -              size_t buf_size)
>> +              size_t buf_size,
>> +              bool truncate)
>>   {
>>       int ret = -1;
>>       int fd = -1;
>> @@ -224,7 +231,8 @@ pci_read_file(const char *path,
>>           goto cleanup;
>>       }
>>   
>> -    if (ftruncate(fd, 0) < 0)
>> +    if (truncate &&
>> +        ftruncate(fd, 0) < 0)
>>           goto cleanup;
>>   
>>       ret = 0;
>> @@ -398,6 +406,8 @@ pci_device_new_from_stub(const struct pciDevice *data)
>>           ABORT("@tmp overflow");
>>       make_file(devpath, "class", tmp, -1);
>>   
>> +    make_file(devpath, "driver_override", NULL, -1);
>> +
>>       if (snprintf(tmp, sizeof(tmp),
>>                    "%s/../../../kernel/iommu_groups/%d",
>>                    devpath, dev->iommuGroup) < 0) {
>> @@ -441,7 +451,7 @@ pci_device_find_by_content(const char *path)
>>   {
>>       char tmp[32];
>>   
>> -    if (pci_read_file(path, tmp, sizeof(tmp)) < 0)
>> +    if (pci_read_file(path, tmp, sizeof(tmp), true) < 0)
>>           return NULL;
>>   
>>       return pci_device_find_by_id(tmp);
>> @@ -450,7 +460,10 @@ pci_device_find_by_content(const char *path)
>>   static int
>>   pci_device_autobind(struct pciDevice *dev)
>>   {
>> -    struct pciDriver *driver = pci_driver_find_by_dev(dev);
>> +    struct pciDriver *driver = pci_driver_find_by_driver_override(dev);
>> +
>> +    if (!driver)
>> +        driver = pci_driver_find_by_dev(dev);

This could explain why the check from 03/31 can't be here. If it was, 
then nor 'driver_override' would be able to bind a PCI device to the 
vfio-pci driver (which obviously is not the case).

>>   
>>       if (!driver) {
>>           /* No driver found. Nothing to do */
>> @@ -544,6 +557,36 @@ pci_driver_find_by_path(const char *path)
>>       return NULL;
>>   }
>>   
>> +static struct pciDriver *
>> +pci_driver_find_by_driver_override(struct pciDevice *dev)
>> +{
>> +    struct pciDriver *ret = NULL;
>> +    char *path = NULL;
>> +    char tmp[32];
>> +    size_t i;
>> +
>> +    if (virAsprintfQuiet(&path,
>> +                         SYSFS_PCI_PREFIX "devices/%s/driver_override",
>> +                         dev->id) < 0)
>> +        return NULL;
>> +
>> +    if (pci_read_file(path, tmp, sizeof(tmp), false) < 0)
>> +        goto cleanup;
>> +
>> +    for (i = 0; i < nPCIDrivers; i++) {
>> +        struct pciDriver *driver = pciDrivers[i];
>> +
>> +        if (STREQ(tmp, driver->name)) {
>> +            ret = driver;
>> +            break;
>> +        }
>> +    }
>> +
>> + cleanup:
>> +    VIR_FREE(path);
> 
> VIR_AUTOFREE should be available.

Ah, good point. Consider fixed.

Michal