| Message ID | 1566240335-6614-1-git-send-email-igor.druzhinin@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | tools/oxenstored: port XS_INTRODUCE evtchn rebind function from cxenstored | expand |
> + if (Domain.get_mfn edom) = mfn && (Connections.find_domain cons domid) != con then begin This should use <> instead of != because != is pointer inequality in OCaml. The parentheses are not strictly necessary because function application has precedence. So: if Domain.get_mfn edom = mfn && Connections.find_domain cons domid <> con then begin — Christian > On 19 Aug 2019, at 19:45, Igor Druzhinin <igor.druzhinin@citrix.com> wrote: > > C version of xenstored had this ability since 61aaed0d5 ("Allow > XS_INTRODUCE to be used for rebinding the xenstore evtchn.") from 2007. > Copy it as is to Ocaml version. > > Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> > --- > tools/ocaml/xenstored/domain.ml | 6 +++++- > tools/ocaml/xenstored/process.ml | 8 +++++++- > 2 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/tools/ocaml/xenstored/domain.ml b/tools/ocaml/xenstored/domain.ml > index b0a01b0..aeb185f 100644 > --- a/tools/ocaml/xenstored/domain.ml > +++ b/tools/ocaml/xenstored/domain.ml > @@ -23,9 +23,9 @@ type t = > { > id: Xenctrl.domid; > mfn: nativeint; > - remote_port: int; > interface: Xenmmap.mmap_interface; > eventchn: Event.t; > + mutable remote_port: int; > mutable port: Xeneventchn.t option; > mutable bad_client: bool; > mutable io_credit: int; (* the rounds of ring process left to do, default is 0, > @@ -71,6 +71,10 @@ let notify dom = match dom.port with > Event.notify dom.eventchn port > > let bind_interdomain dom = > + begin match dom.port with > + | None -> () > + | Some port -> Event.unbind dom.eventchn port > + end; > dom.port <- Some (Event.bind_interdomain dom.eventchn dom.id dom.remote_port); > debug "bound domain %d remote port %d to local port %s" dom.id dom.remote_port (string_of_port dom.port) > > diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml > index 8a7e538..ff5c948 100644 > --- a/tools/ocaml/xenstored/process.ml > +++ b/tools/ocaml/xenstored/process.ml > @@ -408,7 +408,13 @@ let do_introduce con _t domains cons data = > in > let dom = > if Domains.exist domains domid then > - Domains.find domains domid > + let edom = Domains.find domains domid in > + if (Domain.get_mfn edom) = mfn && (Connections.find_domain cons domid) != con then begin > + (* Use XS_INTRODUCE for recreating the xenbus event-channel. *) > + edom.remote_port <- port; > + Domain.bind_interdomain edom; > + end; > + edom > else try > let ndom = Domains.create domains domid mfn port in > Connections.add_domain cons ndom; > -- > 2.7.4 >
On 20/08/2019 09:21, Christian Lindig wrote: >> + if (Domain.get_mfn edom) = mfn && (Connections.find_domain cons domid) != con then begin > > This should use <> instead of != because != is pointer inequality in OCaml. The parentheses are not strictly necessary because function application has precedence. So: > > if Domain.get_mfn edom = mfn && Connections.find_domain cons domid <> con then begin > But I actually want to compare pointers here - the idea is that the connection object in the hashtable indexed by domid is not the same as connection that we got XS_INTRODUCE message from. (see tools/xenstore/xenstrored_domain.c) Igor >> On 19 Aug 2019, at 19:45, Igor Druzhinin <igor.druzhinin@citrix.com> wrote: >> >> C version of xenstored had this ability since 61aaed0d5 ("Allow >> XS_INTRODUCE to be used for rebinding the xenstore evtchn.") from 2007. >> Copy it as is to Ocaml version. >> >> Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> >> --- >> tools/ocaml/xenstored/domain.ml | 6 +++++- >> tools/ocaml/xenstored/process.ml | 8 +++++++- >> 2 files changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/tools/ocaml/xenstored/domain.ml b/tools/ocaml/xenstored/domain.ml >> index b0a01b0..aeb185f 100644 >> --- a/tools/ocaml/xenstored/domain.ml >> +++ b/tools/ocaml/xenstored/domain.ml >> @@ -23,9 +23,9 @@ type t = >> { >> id: Xenctrl.domid; >> mfn: nativeint; >> - remote_port: int; >> interface: Xenmmap.mmap_interface; >> eventchn: Event.t; >> + mutable remote_port: int; >> mutable port: Xeneventchn.t option; >> mutable bad_client: bool; >> mutable io_credit: int; (* the rounds of ring process left to do, default is 0, >> @@ -71,6 +71,10 @@ let notify dom = match dom.port with >> Event.notify dom.eventchn port >> >> let bind_interdomain dom = >> + begin match dom.port with >> + | None -> () >> + | Some port -> Event.unbind dom.eventchn port >> + end; >> dom.port <- Some (Event.bind_interdomain dom.eventchn dom.id dom.remote_port); >> debug "bound domain %d remote port %d to local port %s" dom.id dom.remote_port (string_of_port dom.port) >> >> diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml >> index 8a7e538..ff5c948 100644 >> --- a/tools/ocaml/xenstored/process.ml >> +++ b/tools/ocaml/xenstored/process.ml >> @@ -408,7 +408,13 @@ let do_introduce con _t domains cons data = >> in >> let dom = >> if Domains.exist domains domid then >> - Domains.find domains domid >> + let edom = Domains.find domains domid in >> + if (Domain.get_mfn edom) = mfn && (Connections.find_domain cons domid) != con then begin >> + (* Use XS_INTRODUCE for recreating the xenbus event-channel. *) >> + edom.remote_port <- port; >> + Domain.bind_interdomain edom; >> + end; >> + edom >> else try >> let ndom = Domains.create domains domid mfn port in >> Connections.add_domain cons ndom; >> -- >> 2.7.4 >> >
> On 20 Aug 2019, at 11:45, Igor Druzhinin <igor.druzhinin@citrix.com> wrote: > > On 20/08/2019 09:21, Christian Lindig wrote: >>> + if (Domain.get_mfn edom) = mfn && (Connections.find_domain cons domid) != con then begin >> >> This should use <> instead of != because != is pointer inequality in OCaml. The parentheses are not strictly necessary because function application has precedence. So: >> >> if Domain.get_mfn edom = mfn && Connections.find_domain cons domid <> con then begin >> > > But I actually want to compare pointers here - the idea is that the > connection object in the hashtable indexed by domid is not the same as > connection that we got XS_INTRODUCE message from. (see > tools/xenstore/xenstrored_domain.c) In your code, a != b is true, if a and b have identical structure but different addresses. I strongly suspect that two connection values should have different structure to be considered different, not just different addresses. When a <> b is true, it implies a != b. So using a <> b is safe(r). By using != you would rely on an invariant that every connection (con) exists only once and is never copied. — Christian
On 20/08/2019 13:11, Christian Lindig wrote: > > >> On 20 Aug 2019, at 11:45, Igor Druzhinin <igor.druzhinin@citrix.com> wrote: >> >> On 20/08/2019 09:21, Christian Lindig wrote: >>>> + if (Domain.get_mfn edom) = mfn && (Connections.find_domain cons domid) != con then begin >>> >>> This should use <> instead of != because != is pointer inequality in OCaml. The parentheses are not strictly necessary because function application has precedence. So: >>> >>> if Domain.get_mfn edom = mfn && Connections.find_domain cons domid <> con then begin >>> >> >> But I actually want to compare pointers here - the idea is that the >> connection object in the hashtable indexed by domid is not the same as >> connection that we got XS_INTRODUCE message from. (see >> tools/xenstore/xenstrored_domain.c) > > In your code, a != b is true, if a and b have identical structure but different addresses. I strongly suspect that two connection values should have different structure to be considered different, not just different addresses. When a <> b is true, it implies a != b. So using a <> b is safe(r). By using != you would rely on an invariant that every connection (con) exists only once and is never copied. > Connection is a complex object (has various counters and internal structures) and I don't think simple field by field comparison (is <> just that in Ocaml?) is appropriate here. con is passed into that function from xenstored.ml where it's extracted from the same hashtable (Connections) so it's actually the exactly same object. There are other examples in connections.ml where pointer comparison is used to compare connections. Igor
> On 20 Aug 2019, at 13:45, Igor Druzhinin <igor.druzhinin@citrix.com> wrote: > > con is passed into that function from xenstored.ml where it's extracted > from the same hashtable (Connections) so it's actually the exactly same > object. This comes down to what semantics you want. It is unfortunate that Connection.t is not abstract and its equality not well defined. Using != now relies on the fact that you only compare values stored in the same hash table. — C Acked-by: Christian Lindig <christian.lindig@citrix.com>
diff --git a/tools/ocaml/xenstored/domain.ml b/tools/ocaml/xenstored/domain.ml index b0a01b0..aeb185f 100644 --- a/tools/ocaml/xenstored/domain.ml +++ b/tools/ocaml/xenstored/domain.ml @@ -23,9 +23,9 @@ type t = { id: Xenctrl.domid; mfn: nativeint; - remote_port: int; interface: Xenmmap.mmap_interface; eventchn: Event.t; + mutable remote_port: int; mutable port: Xeneventchn.t option; mutable bad_client: bool; mutable io_credit: int; (* the rounds of ring process left to do, default is 0, @@ -71,6 +71,10 @@ let notify dom = match dom.port with Event.notify dom.eventchn port let bind_interdomain dom = + begin match dom.port with + | None -> () + | Some port -> Event.unbind dom.eventchn port + end; dom.port <- Some (Event.bind_interdomain dom.eventchn dom.id dom.remote_port); debug "bound domain %d remote port %d to local port %s" dom.id dom.remote_port (string_of_port dom.port) diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml index 8a7e538..ff5c948 100644 --- a/tools/ocaml/xenstored/process.ml +++ b/tools/ocaml/xenstored/process.ml @@ -408,7 +408,13 @@ let do_introduce con _t domains cons data = in let dom = if Domains.exist domains domid then - Domains.find domains domid + let edom = Domains.find domains domid in + if (Domain.get_mfn edom) = mfn && (Connections.find_domain cons domid) != con then begin + (* Use XS_INTRODUCE for recreating the xenbus event-channel. *) + edom.remote_port <- port; + Domain.bind_interdomain edom; + end; + edom else try let ndom = Domains.create domains domid mfn port in Connections.add_domain cons ndom;
C version of xenstored had this ability since 61aaed0d5 ("Allow XS_INTRODUCE to be used for rebinding the xenstore evtchn.") from 2007. Copy it as is to Ocaml version. Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> --- tools/ocaml/xenstored/domain.ml | 6 +++++- tools/ocaml/xenstored/process.ml | 8 +++++++- 2 files changed, 12 insertions(+), 2 deletions(-)