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Tue, 29 Oct 2019 02:27:02 +0000 (UTC) Date: Tue, 29 Oct 2019 02:26:59 +0000 From: "Dr. David Alan Gilbert" To: Laszlo Ersek Subject: Re: [PATCH] fw_cfg: Allow reboot-timeout=-1 again Message-ID: <20191029022659.GD2508@work-vm> References: <20191025165706.177653-1-dgilbert@redhat.com> <37ac197c-f20e-dd05-ff6a-13a2171c7148@redhat.com> MIME-Version: 1.0 In-Reply-To: <37ac197c-f20e-dd05-ff6a-13a2171c7148@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: ow0BY0V2OPGrqiNrzjmU9w-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline 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, philmd@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, kraxel@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Laszlo Ersek (lersek@redhat.com) wrote: > 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 documen= t > > the special value -1 to mean don't reboot. > > Allow it again. > > > > Fixes: ee5d0f89de3e53cdb0dc ("fw_cfg: Fix -boot reboot-timeout error ch= ecking") > > 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); > > } > > } > > >=20 > Ouch. >=20 > Here's the prototype of qemu_opt_get_number(): >=20 > > uint64_t qemu_opt_get_number(QemuOpts *opts, const char *name, uint64_t= defval); >=20 > So, when we call it, here's what we actually do: >=20 > rt_val =3D (int64_t)qemu_opt_get_number(opts, "reboot-timeout", (= uint64_t)-1); > ^^^^^^^^^ ^^^= ^^^^^^^ >=20 > The conversion to uint64_t is fine. >=20 > The conversion to int64_t is not great: >=20 > > 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. >=20 > I guess we're exploiting two's complement, as the implementation-defined > result. Not great. :) >=20 > Here's what I'd prefer: >=20 > > 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); > > } > > } I think I'm fine with that as well; want to add a signed off and post? > ( >=20 > The trick is that strtoull(), in >=20 > qemu_opt_get_number() > qemu_opt_get_number_helper() > parse_option_number() > qemu_strtou64() > strtoull() >=20 > turns "-1" into (uint64_t)-1, which counts as a valid conversion, per > spec: It's rather scary how much we rely on the grubby depths of the implementations of our conversion routines. > > 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. >=20 > ) >=20 > I don't insist though; if Phil is OK with the posted patch, I won't try > to block it. I'm happy either way. Dave > Thanks > Laszlo -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK