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Mon, 22 Jun 2020 17:54:28 +0000 (UTC) Date: Mon, 22 Jun 2020 18:54:25 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Michal Privoznik Subject: Re: [PATCH v2 1/2] util: Introduce qemu_get_host_name() Message-ID: <20200622175425.GP736373@redhat.com> References: <567f969602c1742e23c7760944e909346b2d012b.1592846572.git.mprivozn@redhat.com> <20200622173849.GN736373@redhat.com> <80586aa2-c02b-54a3-cf10-d7cda297cfbd@redhat.com> MIME-Version: 1.0 In-Reply-To: <80586aa2-c02b-54a3-cf10-d7cda297cfbd@redhat.com> User-Agent: Mutt/1.14.0 (2020-05-02) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=berrange@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, URIBL_BLOCKED=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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 Mon, Jun 22, 2020 at 07:53:40PM +0200, Michal Privoznik wrote: > 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. Oh right, yes, I'm mis-reading the code. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|