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Fri, 25 Oct 2019 21:28:05 +0000 (UTC) Subject: Re: [PATCH] fw_cfg: Allow reboot-timeout=-1 again To: "Dr. David Alan Gilbert (git)" , qemu-devel@nongnu.org, philmd@redhat.com, kraxel@redhat.com References: <20191025165706.177653-1-dgilbert@redhat.com> From: Laszlo Ersek Message-ID: <37ac197c-f20e-dd05-ff6a-13a2171c7148@redhat.com> Date: Fri, 25 Oct 2019 23:28:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20191025165706.177653-1-dgilbert@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: F75pepwgPS6bflOq5yM1YA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.61 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: liq3ea@gmail.com, armbru@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/25/19 18:57, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" > > Commit ee5d0f89de3e53cdb0dc added range checking on reboot-timeout > to only allow the range 0..65535; however both qemu and libvirt document > the special value -1 to mean don't reboot. > Allow it again. > > Fixes: ee5d0f89de3e53cdb0dc ("fw_cfg: Fix -boot reboot-timeout error chec= king") > RH bz: https://bugzilla.redhat.com/show_bug.cgi?id=3D1765443 > Signed-off-by: Dr. David Alan Gilbert > --- > hw/nvram/fw_cfg.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c > index 7dc3ac378e..1a9ec44232 100644 > --- a/hw/nvram/fw_cfg.c > +++ b/hw/nvram/fw_cfg.c > @@ -247,10 +247,11 @@ static void fw_cfg_reboot(FWCfgState *s) > > if (reboot_timeout) { > rt_val =3D qemu_opt_get_number(opts, "reboot-timeout", -1); > + > /* validate the input */ > - if (rt_val < 0 || rt_val > 0xffff) { > + if (rt_val < -1 || rt_val > 0xffff) { > error_report("reboot timeout is invalid," > - "it should be a value between 0 and 65535"); > + "it should be a value between -1 and 65535"); > exit(1); > } > } > Ouch. Here's the prototype of qemu_opt_get_number(): > uint64_t qemu_opt_get_number(QemuOpts *opts, const char *name, uint64_t d= efval); So, when we call it, here's what we actually do: rt_val =3D (int64_t)qemu_opt_get_number(opts, "reboot-timeout", (ui= nt64_t)-1); ^^^^^^^^^ ^^^^^= ^^^^^ The conversion to uint64_t is fine. The conversion to int64_t is not great: > Otherwise, the new type is signed and the value cannot be represented > in it; either the result is implementation-defined or an > implementation-defined signal is raised. I guess we're exploiting two's complement, as the implementation-defined result. Not great. :) Here's what I'd prefer: > diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c > index 7dc3ac378ee0..16413550a1da 100644 > --- a/hw/nvram/fw_cfg.c > +++ b/hw/nvram/fw_cfg.c > @@ -237,7 +237,7 @@ static void fw_cfg_bootsplash(FWCfgState *s) > static void fw_cfg_reboot(FWCfgState *s) > { > const char *reboot_timeout =3D NULL; > - int64_t rt_val =3D -1; > + uint64_t rt_val =3D -1; > uint32_t rt_le32; > > /* get user configuration */ > @@ -248,9 +248,9 @@ static void fw_cfg_reboot(FWCfgState *s) > if (reboot_timeout) { > rt_val =3D qemu_opt_get_number(opts, "reboot-timeout", -1); > /* validate the input */ > - if (rt_val < 0 || rt_val > 0xffff) { > + if (rt_val > 0xffff && rt_val !=3D (uint64_t)-1) { > error_report("reboot timeout is invalid," > - "it should be a value between 0 and 65535"); > + "it should be a value between -1 and 65535"); > exit(1); > } > } ( The trick is that strtoull(), in qemu_opt_get_number() qemu_opt_get_number_helper() parse_option_number() qemu_strtou64() strtoull() turns "-1" into (uint64_t)-1, which counts as a valid conversion, per spec: > If the subject sequence has the expected form and the value of /base/ > is zero, the sequence of characters starting with the first digit is > interpreted as an integer constant according to the rules of 6.4.4.1. > If the subject sequence has the expected form and the value of /base/ > is between 2 and 36, it is used as the base for conversion, ascribing > to each letter its value as given above. If the subject sequence > begins with a minus sign, the value resulting from the conversion is > negated (in the return type). A pointer to the final string is stored > in the object pointed to by /endptr/, provided that /endptr/ is not a > null pointer. ) I don't insist though; if Phil is OK with the posted patch, I won't try to block it. Thanks Laszlo