Re: [Qemu-devel] [PATCH v2] bugfix: passing reference instead of value

[Cao jin <caoj.fnst@cn.fujitsu.com>]

Hi Paolo

On 12/30/2015 12:25 AM, Paolo Bonzini wrote:
>>>> Separated from previous "igd-passthru convert to realize" patch. Since
>>>> these two don`t have dependency, can send it solely.
>>>>
>>>> Not test since it is easy to find out if reading carefully, just
>>>> compiled.
>
> This patch works but the added conversion to LE is conceptually wrong.
> The conversion from LE to CPU and vice versa is already done by
> host_pci_config_read and pci_default_write_config.  You don't have it in
> host_pci_config_read because the code is not portable and x86 is
> little-endian.
>

Do you mean, this code section(or this igd passthru device)will only run 
on x86? If it is, yes, the cpu_to_le32() is not necessary. If it has 
opportunity to run on BE, I think it is necessary, right?

The reason I add the conversion is that I am not sure whether it will 
run on a BE machine or not, and it will no bad to LE machine like x86.

> Generally, functions that accept/return integers take care themselves of
> endianness conversions.
>
> Paolo
>
>
>>>>    hw/pci-host/piix.c | 10 ++++++----
>>>>    1 file changed, 6 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
>>>> index 715208b..a9cb983 100644
>>>> --- a/hw/pci-host/piix.c
>>>> +++ b/hw/pci-host/piix.c
>>>> @@ -761,7 +761,7 @@ static const IGDHostInfo igd_host_bridge_infos[] = {
>>>>        {0xa8, 4},  /* SNB: base of GTT stolen memory */
>>>>    };
>>>>
>>>> -static int host_pci_config_read(int pos, int len, uint32_t val)
>>>> +static int host_pci_config_read(int pos, int len, uint32_t *val)
>>>>    {
>>>>        char path[PATH_MAX];
>>>>        int config_fd;
>>>> @@ -784,12 +784,14 @@ static int host_pci_config_read(int pos, int
>>>> len, uint32_t val)
>>>>            ret = -errno;
>>>>            goto out;
>>>>        }
>>>> +
>>>>        do {
>>>> -        rc = read(config_fd, (uint8_t *)&val, len);
>>>> +        rc = read(config_fd, (uint8_t *)val, len);
>>>>        } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>>>>        if (rc != len) {
>>>>            ret = -errno;
>>>>        }
>>>> +
>>>>    out:
>>>>        close(config_fd);
>>>>        return ret;
>>>> @@ -805,11 +807,11 @@ static int igd_pt_i440fx_initfn(struct PCIDevice
>>>> *pci_dev)
>>>>        for (i = 0; i < num; i++) {
>>>>            pos = igd_host_bridge_infos[i].offset;
>>>>            len = igd_host_bridge_infos[i].len;
>>>> -        rc = host_pci_config_read(pos, len, val);
>>>> +        rc = host_pci_config_read(pos, len, &val);
>>>>            if (rc) {
>>>>                return -ENODEV;
>>>>            }
>>>> -        pci_default_write_config(pci_dev, pos, val, len);
>>>> +        pci_default_write_config(pci_dev, pos, cpu_to_le32(val), len);
>>>>        }
>>>>
>>>>        return 0;
>>>>
>>>
>>
>
>
> .
>

-- 
Yours Sincerely,

Cao Jin