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Mon, 22 Jun 2020 17:53:41 +0000 (UTC) Subject: Re: [PATCH v2 1/2] util: Introduce qemu_get_host_name() To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <567f969602c1742e23c7760944e909346b2d012b.1592846572.git.mprivozn@redhat.com> <20200622173849.GN736373@redhat.com> From: Michal Privoznik Message-ID: <80586aa2-c02b-54a3-cf10-d7cda297cfbd@redhat.com> Date: Mon, 22 Jun 2020 19:53:40 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200622173849.GN736373@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=mprivozn@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/22 03:17:49 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: vfeenstr@redhat.com, sw@weilnetz.de, mdroth@linux.vnet.ibm.com, qemu-devel@nongnu.org, marcandre.lureau@gmail.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/22/20 7:38 PM, Daniel P. Berrangé wrote: > On Mon, Jun 22, 2020 at 07:26:44PM +0200, Michal Privoznik wrote: >> This function offers operating system agnostic way to fetch host >> name. It is implemented for both POSIX-like and Windows systems. >> >> Signed-off-by: Michal Privoznik >> --- >> include/qemu/osdep.h | 10 ++++++++++ >> util/oslib-posix.c | 32 ++++++++++++++++++++++++++++++++ >> util/oslib-win32.c | 13 +++++++++++++ >> 3 files changed, 55 insertions(+) >> >> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h >> index ff7c17b857..a795d46b28 100644 >> --- a/include/qemu/osdep.h >> +++ b/include/qemu/osdep.h >> @@ -607,4 +607,14 @@ static inline void qemu_reset_optind(void) >> #endif >> } >> >> +/** >> + * qemu_get_host_name: >> + * @errp: Error object >> + * >> + * Operating system agnostic way of querying host name. >> + * >> + * Returns allocated hostname (caller should free), NULL on failure. >> + */ >> +char *qemu_get_host_name(Error **errp); >> + >> #endif >> diff --git a/util/oslib-posix.c b/util/oslib-posix.c >> index 916f1be224..865a3d71a7 100644 >> --- a/util/oslib-posix.c >> +++ b/util/oslib-posix.c >> @@ -761,3 +761,35 @@ void sigaction_invoke(struct sigaction *action, >> } >> action->sa_sigaction(info->ssi_signo, &si, NULL); >> } >> + >> +#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 >> + >> +char *qemu_get_host_name(Error **errp) >> +{ >> + long len = -1; >> + char *hostname; >> + >> +#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); > > Nitpick, generally qemu prefers g_new0 > >> + >> + if (gethostname(hostname, len) < 0) { >> + error_setg_errno(errp, errno, >> + "cannot get hostname"); >> + return NULL; >> + } > > According to my man page, it is undefined by POSIX whether there's a > trailing NUL when hostname exceeds the buffer, so the paranoid thing > todo is to add > > hostname[len] = '\0'; Isn't this guaranteed by allocating len + 1 bytes? I mean, g_malloc0() and g_new0() will memset() the memory to zero. And since I tell gethostname() the buf is only len bytes long I am guaranteed to have 0 at the end of it, aren't I? Maybe I should put a comment just before g_malloc0() or g_new0() that documents this thought. Michal