* [PATCH] qga: Use gethostname() instead of g_get_host_name()
@ 2020-06-16 8:34 Michal Privoznik
2020-06-16 8:43 ` Marc-André Lureau
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Michal Privoznik @ 2020-06-16 8:34 UTC (permalink / raw)
To: qemu-devel; +Cc: vfeenstr, mdroth
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.
+ */
+
+#ifndef G_OS_WIN32
+ long len = -1;
+
+#ifdef _SC_HOST_NAME_MAX
+ len = sysconf(_SC_HOST_NAME_MAX);
+#endif /* _SC_HOST_NAME_MAX */
+
+ if (len < 0) {
+ len = HOST_NAME_MAX;
}
+
+ hostname = g_malloc0(len + 1);
+
+ if (gethostname(hostname, len) < 0) {
+ return NULL;
+ }
+
+#else /* G_OS_WIN32 */
+
+ wchar_t tmp[MAX_COMPUTERNAME_LENGTH + 1];
+ DWORD size = G_N_ELEMENTS(tmp);
+
+ if (GetComputerNameW(tmp, &size) != 0) {
+ /*
+ * Indeed, on Windows retval of zero means failure
+ * and nonzero means success.
+ */
+ hostname = g_utf16_to_utf8(tmp, size, NULL, NULL, NULL);
+ }
+#endif /* G_OS_WIN32 */
+
+ if (!hostname) {
+ hostname = g_strdup("localhost");
+ }
+
+ result = g_new0(GuestHostName, 1);
+ result->host_name = g_steal_pointer(&hostname);
return result;
}
--
2.26.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] qga: Use gethostname() instead of g_get_host_name()
2020-06-16 8:34 [PATCH] qga: Use gethostname() instead of g_get_host_name() Michal Privoznik
@ 2020-06-16 8:43 ` Marc-André Lureau
2020-06-19 21:54 ` Richard Henderson
2020-06-22 10:14 ` Philippe Mathieu-Daudé
2 siblings, 0 replies; 6+ messages in thread
From: Marc-André Lureau @ 2020-06-16 8:43 UTC (permalink / raw)
To: Michal Privoznik
Cc: Michael Roth, QEMU, Vinzenz 'evilissimo' Feenstra
[-- Attachment #1: Type: text/plain, Size: 2916 bytes --]
Hi
On Tue, Jun 16, 2020 at 12:35 PM Michal Privoznik <mprivozn@redhat.com>
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
lgtm,
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
(fwiw, I opened a glib issue:
https://gitlab.gnome.org/GNOME/glib/-/issues/2130)
>
> 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.
> + */
> +
> +#ifndef G_OS_WIN32
> + long len = -1;
> +
> +#ifdef _SC_HOST_NAME_MAX
> + len = sysconf(_SC_HOST_NAME_MAX);
> +#endif /* _SC_HOST_NAME_MAX */
> +
> + if (len < 0) {
> + len = HOST_NAME_MAX;
> }
> +
> + hostname = g_malloc0(len + 1);
> +
> + if (gethostname(hostname, len) < 0) {
> + return NULL;
> + }
> +
> +#else /* G_OS_WIN32 */
> +
> + wchar_t tmp[MAX_COMPUTERNAME_LENGTH + 1];
> + DWORD size = G_N_ELEMENTS(tmp);
> +
> + if (GetComputerNameW(tmp, &size) != 0) {
> + /*
> + * Indeed, on Windows retval of zero means failure
> + * and nonzero means success.
> + */
> + hostname = g_utf16_to_utf8(tmp, size, NULL, NULL, NULL);
> + }
> +#endif /* G_OS_WIN32 */
> +
> + if (!hostname) {
> + hostname = g_strdup("localhost");
> + }
> +
> + result = g_new0(GuestHostName, 1);
> + result->host_name = g_steal_pointer(&hostname);
> return result;
> }
>
> --
> 2.26.2
>
>
>
--
Marc-André Lureau
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] qga: Use gethostname() instead of g_get_host_name()
2020-06-16 8:34 [PATCH] qga: Use gethostname() instead of g_get_host_name() Michal Privoznik
2020-06-16 8:43 ` Marc-André Lureau
@ 2020-06-19 21:54 ` Richard Henderson
2020-06-22 10:06 ` Michal Privoznik
2020-06-22 10:14 ` Philippe Mathieu-Daudé
2 siblings, 1 reply; 6+ messages in thread
From: Richard Henderson @ 2020-06-19 21:54 UTC (permalink / raw)
To: Michal Privoznik, qemu-devel; +Cc: vfeenstr, mdroth
On 6/16/20 1:34 AM, Michal Privoznik wrote:
> +#ifndef G_OS_WIN32
Nit: positive tests are easier to reason with and extend than negative tests.
I would reverse these two blocks and use a positive test for windows.
Also, CONFIG_WIN32 is what we use elsewhere for this test.
r~
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] qga: Use gethostname() instead of g_get_host_name()
2020-06-19 21:54 ` Richard Henderson
@ 2020-06-22 10:06 ` Michal Privoznik
0 siblings, 0 replies; 6+ messages in thread
From: Michal Privoznik @ 2020-06-22 10:06 UTC (permalink / raw)
To: Richard Henderson, qemu-devel; +Cc: vfeenstr, mdroth
On 6/19/20 11:54 PM, Richard Henderson wrote:
> On 6/16/20 1:34 AM, Michal Privoznik wrote:
>> +#ifndef G_OS_WIN32
>
> Nit: positive tests are easier to reason with and extend than negative tests.
> I would reverse these two blocks and use a positive test for windows.
>
> Also, CONFIG_WIN32 is what we use elsewhere for this test.
>
>
> r~
>
Fair enough. Do you want me to send v2 or is it something that committer
can fix before merging?
Michal
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] qga: Use gethostname() instead of g_get_host_name()
2020-06-16 8:34 [PATCH] qga: Use gethostname() instead of g_get_host_name() Michal Privoznik
2020-06-16 8:43 ` Marc-André Lureau
2020-06-19 21:54 ` Richard Henderson
@ 2020-06-22 10:14 ` Philippe Mathieu-Daudé
2020-06-22 13:08 ` Michal Privoznik
2 siblings, 1 reply; 6+ messages in thread
From: Philippe Mathieu-Daudé @ 2020-06-22 10:14 UTC (permalink / raw)
To: Michal Privoznik, qemu-devel; +Cc: vfeenstr, mdroth
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?
> +
> +#ifndef G_OS_WIN32
> + long len = -1;
> +
> +#ifdef _SC_HOST_NAME_MAX
> + len = sysconf(_SC_HOST_NAME_MAX);
> +#endif /* _SC_HOST_NAME_MAX */
> +
> + if (len < 0) {
> + len = HOST_NAME_MAX;
> }
> +
> + hostname = g_malloc0(len + 1);
> +
> + if (gethostname(hostname, len) < 0) {
> + return NULL;
> + }
> +
> +#else /* G_OS_WIN32 */
> +
> + wchar_t tmp[MAX_COMPUTERNAME_LENGTH + 1];
> + DWORD size = G_N_ELEMENTS(tmp);
> +
> + if (GetComputerNameW(tmp, &size) != 0) {
> + /*
> + * Indeed, on Windows retval of zero means failure
> + * and nonzero means success.
> + */
> + hostname = g_utf16_to_utf8(tmp, size, NULL, NULL, NULL);
> + }
> +#endif /* G_OS_WIN32 */
> +
> + if (!hostname) {
> + hostname = g_strdup("localhost");
> + }
> +
> + result = g_new0(GuestHostName, 1);
> + result->host_name = g_steal_pointer(&hostname);
> return result;
> }
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] qga: Use gethostname() instead of g_get_host_name()
2020-06-22 10:14 ` Philippe Mathieu-Daudé
@ 2020-06-22 13:08 ` Michal Privoznik
0 siblings, 0 replies; 6+ messages in thread
From: Michal Privoznik @ 2020-06-22 13:08 UTC (permalink / raw)
To: Philippe Mathieu-Daudé, qemu-devel
Cc: Richard Henderson, vfeenstr, mdroth
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
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-06-22 13:11 UTC | newest]
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-- links below jump to the message on this page --
2020-06-16 8:34 [PATCH] qga: Use gethostname() instead of g_get_host_name() Michal Privoznik
2020-06-16 8:43 ` Marc-André Lureau
2020-06-19 21:54 ` Richard Henderson
2020-06-22 10:06 ` Michal Privoznik
2020-06-22 10:14 ` Philippe Mathieu-Daudé
2020-06-22 13:08 ` Michal Privoznik
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