Re: [Xen-devel] [PATCH 3/3] xen-init-dom0: set Dom0 UUID if requested

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/11/2018 13:35, Wei Liu wrote:
> On Thu, Nov 15, 2018 at 11:20:37AM +0000, Wei Liu wrote:
>> On Thu, Nov 15, 2018 at 10:45:52AM +0000, Edwin Török wrote:
>>> On 14/11/2018 18:17, Wei Liu wrote:
>>>> Read from XEN_CONFIG_DIR/dom0-uuid. If it contains a valid UUID, set
>>>> it for Dom0.
>>>>
>>>> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
>>> [snip]
>>> In general this looks good, however I am not familiar with libxl
>>> conventions, so just some generic comments below.
>>>
>>>> +static void get_dom0_uuid(libxl_uuid *uuid)
>>>> +{
>>>> +    int fd = -1;
>>>> +    ssize_t r;
>>>> +    char uuid_buf[LIBXL_UUID_FMTLEN+1];
>>>> +
>>>> +    libxl_uuid_clear(uuid);
>>>> +
>>>> +    fd = open(DOM0_UUID_PATH, O_RDONLY);
>>>> +    if (fd < 0) {
>>>> +        fprintf(stderr, "failed to open %s\n", DOM0_UUID_PATH);
>>>> +        goto out;
>>>> +    }
>>>> +
>>>> +    r = read(fd, uuid_buf, LIBXL_UUID_FMTLEN);
>>> Could this be a short read? I'm not familiar with libxl conventions, but
>>> would there be a utility function that repeats the read if it is short,
>>> or would fread be better?
>> I can use libxl_read_exactly instead. That saves me from writing some
>> code to handle every corner case.
>>
> On second thought, this requires code to allocating and destroying libxl
> ctx. I will write a loop here to handle short-read instead.

fopen()/fread() will get you the correct behaviour for far less code.

~Andrew

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