Re: [PATCH] qga: Use gethostname() instead of g_get_host_name()

[Michal Privoznik <mprivozn@redhat.com>]

On 6/22/20 12:14 PM, Philippe Mathieu-Daudé wrote:
> Hi Michal,
> 
> On 6/16/20 10:34 AM, Michal Privoznik wrote:
>> Problem with g_get_host_name() is that on the first call it saves
>> the hostname into a global variable and from then on, every
>> subsequent call returns the saved hostname. Even if the hostname
>> changes. This doesn't play nicely with guest agent, because if
>> the hostname is acquired before the guest is set up (e.g. on the
>> first boot, or before DHCP) we will report old, invalid hostname.
>>
>> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1845127
>>
>> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
>> ---
>>   qga/commands.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++----
>>   1 file changed, 52 insertions(+), 4 deletions(-)
>>
>> diff --git a/qga/commands.c b/qga/commands.c
>> index efc8b90281..ce3c2041a6 100644
>> --- a/qga/commands.c
>> +++ b/qga/commands.c
>> @@ -512,14 +512,62 @@ int ga_parse_whence(GuestFileWhence *whence, Error **errp)
>>       return -1;
>>   }
>>   
>> +#ifndef HOST_NAME_MAX
>> +# ifdef _POSIX_HOST_NAME_MAX
>> +#  define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
>> +# else
>> +#  define HOST_NAME_MAX 255
>> +# endif
>> +#endif
>> +
>>   GuestHostName *qmp_guest_get_host_name(Error **errp)
>>   {
>>       GuestHostName *result = NULL;
>> -    gchar const *hostname = g_get_host_name();
>> -    if (hostname != NULL) {
>> -        result = g_new0(GuestHostName, 1);
>> -        result->host_name = g_strdup(hostname);
>> +    g_autofree char *hostname = NULL;
>> +
>> +    /*
>> +     * We want to avoid using g_get_host_name() because that
>> +     * caches the result and we wouldn't reflect changes in the
>> +     * host name.
>> +     */
> 
> I see there is only one g_get_host_name() call in the
> codebase, but can we have a generic qemu_get_host_name()
> helper implemented in util/oslib-*c instead?

Sure. Let me post a v2 so that I can include Richard's suggestion too.

Michal