From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:32848) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1chF0c-0004sD-UI for qemu-devel@nongnu.org; Fri, 24 Feb 2017 07:30:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1chF0Z-00019W-Oi for qemu-devel@nongnu.org; Fri, 24 Feb 2017 07:30:02 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43094) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1chF0Z-00018T-GH for qemu-devel@nongnu.org; Fri, 24 Feb 2017 07:29:59 -0500 Date: Fri, 24 Feb 2017 12:29:55 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20170224122954.GA8830@work-vm> References: <20170222160119.52771-1-pasic@linux.vnet.ibm.com> <20170222160119.52771-4-pasic@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170222160119.52771-4-pasic@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [PATCH v2 3/5] migration/vmstate: fix array of ptr with nullptrs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Halil Pasic Cc: qemu-devel@nongnu.org, Juan Quintela * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > Make VMS_ARRAY_OF_POINTER cope with null pointers. Previously the > reward for trying to migrate an array with some null pointers in it was > an illegal memory access, that is a swift and painless death of the > process. Let's make vmstate cope with this scenario. > > The general approach is, when we encounter a null pointer (element), > instead of following the pointer to save/load the data behind it, we > save/load a placeholder. This way we can detect if we expected a null > pointer at the load side but not null data was saved instead. > > Signed-off-by: Halil Pasic > Reviewed-by: Guenther Hutzl Reviewed-by: Dr. David Alan Gilbert > --- > We will need this to load/save some on demand created state in the > (s390x) channel subsystem (see ChannelSubSys.css in hw/s390x/css.c for > an example). > --- > include/migration/vmstate.h | 4 ++++ > migration/vmstate.c | 40 ++++++++++++++++++++++++++++++++++++++-- > 2 files changed, 42 insertions(+), 2 deletions(-) > > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h > index 63e7b02..f2dbf84 100644 > --- a/include/migration/vmstate.h > +++ b/include/migration/vmstate.h > @@ -253,6 +253,10 @@ extern const VMStateInfo vmstate_info_uint16; > extern const VMStateInfo vmstate_info_uint32; > extern const VMStateInfo vmstate_info_uint64; > > +/** Put this in the stream when migrating a null pointer.*/ > +#define VMS_NULLPTR_MARKER (0x30U) /* '0' */ > +extern const VMStateInfo vmstate_info_nullptr; > + > extern const VMStateInfo vmstate_info_float64; > extern const VMStateInfo vmstate_info_cpudouble; > > diff --git a/migration/vmstate.c b/migration/vmstate.c > index 836a7a4..78b3cd4 100644 > --- a/migration/vmstate.c > +++ b/migration/vmstate.c > @@ -117,7 +117,11 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd, > if (field->flags & VMS_ARRAY_OF_POINTER) { > curr_elem = *(void **)curr_elem; > } > - if (field->flags & VMS_STRUCT) { > + if (!curr_elem) { > + /* if null pointer check placeholder and do not follow */ > + assert(field->flags & VMS_ARRAY_OF_POINTER); > + ret = vmstate_info_nullptr.get(f, curr_elem, size, NULL); > + } else if (field->flags & VMS_STRUCT) { > ret = vmstate_load_state(f, field->vmsd, curr_elem, > field->vmsd->version_id); > } else { > @@ -332,7 +336,11 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd, > assert(curr_elem); > curr_elem = *(void **)curr_elem; > } > - if (field->flags & VMS_STRUCT) { > + if (!curr_elem) { > + /* if null pointer write placeholder and do not follow */ > + assert(field->flags & VMS_ARRAY_OF_POINTER); > + vmstate_info_nullptr.put(f, curr_elem, size, NULL, NULL); > + } else if (field->flags & VMS_STRUCT) { > vmstate_save_state(f, field->vmsd, curr_elem, vmdesc_loop); > } else { > field->info->put(f, curr_elem, size, field, vmdesc_loop); > @@ -747,6 +755,34 @@ const VMStateInfo vmstate_info_uint64 = { > .put = put_uint64, > }; > > +static int get_nullptr(QEMUFile *f, void *pv, size_t size, VMStateField *field) > + > +{ > + if (qemu_get_byte(f) == VMS_NULLPTR_MARKER) { > + return 0; > + } > + error_report("vmstate: get_nullptr expected VMS_NULLPTR_MARKER"); > + return -EINVAL; > +} > + > +static int put_nullptr(QEMUFile *f, void *pv, size_t size, > + VMStateField *field, QJSON *vmdesc) > + > +{ > + if (pv == NULL) { > + qemu_put_byte(f, VMS_NULLPTR_MARKER); > + return 0; > + } > + error_report("vmstate: put_nullptr must be called with pv == NULL"); > + return -EINVAL; > +} > + > +const VMStateInfo vmstate_info_nullptr = { > + .name = "uint64", > + .get = get_nullptr, > + .put = put_nullptr, > +}; > + > /* 64 bit unsigned int. See that the received value is the same than the one > in the field */ > > -- > 2.8.4 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK