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Re: [Qemu-devel] [PATCH v4 7/9] sockets: allow SocketAddress 'fd' to ref
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-devel] [PATCH v4 7/9] sockets: allow SocketAddress 'fd' to reference numeric file descriptors |
Date: |
Tue, 6 Feb 2018 09:13:37 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Mon, Feb 05, 2018 at 01:42:50PM -0600, Eric Blake wrote:
> On 02/05/2018 09:24 AM, Daniel P. Berrangé wrote:
> > From: "Daniel P. Berrange" <address@hidden>
> >
> > The SocketAddress 'fd' kind accepts the name of a file descriptor passed
> > to the monitor with the 'getfd' command. This makes it impossible to use
> > the 'fd' kind in cases where a monitor is not available. This can apply in
> > handling command line argv at startup, or simply if internal code wants to
> > use SocketAddress and pass a numeric FD it has acquired from elsewhere.
> >
> > Fortunately the 'getfd' command mandated that the FD names must not start
> > with a leading digit. We can thus safely extend semantics of the
> > SocketAddress 'fd' kind, to allow a purely numeric name to reference an
> > file descriptor that QEMU already has open. There will be restrictions on
> > when each kind can be used.
> >
> > In codepaths where we are handling a monitor command (ie cur_mon != NULL),
> > we will only support use of named file descriptors as before. Use of FD
> > numbers is still not permitted for monitor commands.
> >
> > In codepaths where we are not handling a monitor command (ie cur_mon ==
> > NULL), we will not support named file descriptors. Instead we can reference
> > FD numers explicitly. This allows the app spawning QEMU to intentionally
> > "leak" a pre-opened socket to QEMU and reference that in a SocketAddress
> > definition, or for code inside QEMU to pass pre-opened FDs around.
> >
> > Reviewed-by: Marc-André Lureau <address@hidden>
> > Signed-off-by: Daniel P. Berrange <address@hidden>
> > ---
> > qapi/sockets.json | 7 +++
> > tests/test-util-sockets.c | 112
> > +++++++++++++++++++++++++++++++++++++++++++---
> > util/qemu-sockets.c | 16 +++++--
> > 3 files changed, 126 insertions(+), 9 deletions(-)
> >
> > diff --git a/qapi/sockets.json b/qapi/sockets.json
> > index ac022c6ad0..fc81d8d5e8 100644
> > --- a/qapi/sockets.json
> > +++ b/qapi/sockets.json
> > @@ -123,6 +123,13 @@
> > #
> > # @unix: Unix domain socket
> > #
> > +# @vsock: VMCI address
> > +#
> > +# @fd: decimal is for file descriptor number, otherwise a file descriptor
> > name.
> > +# Named file descriptors are permitted in monitor commands, in
> > combination
> > +# with the 'getfd' command. Decimal file descriptors are permitted at
> > +# startup or other contexts where no monitor context is active.
> > +#
> > # Since: 2.9
>
> There doesn't seem to be any way to introspect if we support decimal fds
> from the command line; is that going to be a problem?
Libvirt needs to know when it can use it, so any suggestions ?
Regards,
Daniel
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- [Qemu-devel] [PATCH v4 2/9] cutils: add qemu_strtoi & qemu_strtoui parsers for int/unsigned int types, (continued)
- [Qemu-devel] [PATCH v4 2/9] cutils: add qemu_strtoi & qemu_strtoui parsers for int/unsigned int types, Daniel P . Berrangé, 2018/02/05
- [Qemu-devel] [PATCH v4 4/9] sockets: strengthen test suite IP protocol availability checks, Daniel P . Berrangé, 2018/02/05
- [Qemu-devel] [PATCH v4 3/9] sockets: pull code for testing IP availability out of specific test, Daniel P . Berrangé, 2018/02/05
- [Qemu-devel] [PATCH v4 6/9] sockets: check that the named file descriptor is a socket, Daniel P . Berrangé, 2018/02/05
- [Qemu-devel] [PATCH v4 5/9] sockets: move fd_is_socket() into common sockets code, Daniel P . Berrangé, 2018/02/05
- [Qemu-devel] [PATCH v4 7/9] sockets: allow SocketAddress 'fd' to reference numeric file descriptors, Daniel P . Berrangé, 2018/02/05
- [Qemu-devel] [PATCH v4 8/9] char: refactor parsing of socket address information, Daniel P . Berrangé, 2018/02/05
- [Qemu-devel] [PATCH v4 9/9] char: allow passing pre-opened socket file descriptor at startup, Daniel P . Berrangé, 2018/02/05
- Re: [Qemu-devel] [PATCH v4 0/9] Enable passing pre-opened chardev socket FD, no-reply, 2018/02/05