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Subject: Re: [virtio-dev] [PATCH v4 2/3] shared memory: Define PCI capability
On Wed, Jun 19, 2019 at 06:10:45PM +0100, Dr. David Alan Gilbert wrote: > * Michael S. Tsirkin (mst@redhat.com) wrote: > > On Wed, Mar 20, 2019 at 12:07:39PM +0000, Dr. David Alan Gilbert (git) wrote: > > > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com> > > > > > > Define the PCI capability used for enumerating shared memory regions. > > > > > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> > > > Reviewed-by: Cornelia Huck <cohuck@redhat.com> > > > --- > > > content.tex | 37 +++++++++++++++++++++++++++++++++++++ > > > 1 file changed, 37 insertions(+) > > > > > > diff --git a/content.tex b/content.tex > > > index 8cd1a38..ddbf949 100644 > > > --- a/content.tex > > > +++ b/content.tex > > > @@ -688,6 +688,8 @@ The fields are interpreted as follows: > > > #define VIRTIO_PCI_CAP_DEVICE_CFG 4 > > > /* PCI configuration access */ > > > #define VIRTIO_PCI_CAP_PCI_CFG 5 > > > +/* Shared memory region */ > > > +#define VIRTIO_PCI_CAP_SHARED_MEMORY_CFG 8 > > > \end{lstlisting} > > > > > > Any other value is reserved for future use. > > > @@ -1052,6 +1054,41 @@ any device type which has a device-specific configuration. > > > > > > The \field{offset} for the device-specific configuration MUST be 4-byte aligned. > > > > > > +\subsubsection{Shared memory capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Shared memory capability} > > > + > > > +Shared memory regions \ref{sec:Basic Facilities of a Virtio > > > +Device / Shared Memory Regions} are enumerated on the PCI transport > > > +as a sequence of VIRTIO_PCI_CAP_SHARED_MEMORY_CFG capabilities, one per region. > > > + > > > +The capability is immediately followed by an additional field like so: > > > + > > > +\begin{lstlisting} > > > +struct virtio_pci_shm_cap { > > > + struct virtio_pci_cap cap; > > > + u32 offset_hi; > > > + u32 length_hi; > > > + u8 id; > > > > Pls pad, pci capabilities must be a multiple of 4 bytes. > > BTW virtio_pci_cap has 3 bytes of padding. > > We can stick the id there maybe? > > Do you mean changing the def of virtio_pci_cap to: ? > struct virtio_pci_cap { > __u8 cap_vndr; /* Generic PCI field: PCI_CAP_ID_VNDR */ > __u8 cap_next; /* Generic PCI field: next ptr. */ > __u8 cap_len; /* Generic PCI field: capability length */ > __u8 cfg_type; /* Identifies the structure. */ > __u8 bar; /* Where to find it. */ > __u8 id; /* Unique ID for this region */ > __u8 padding[2]; /* Pad to full dword. */ > __le32 offset; /* Offset within bar. */ > __le32 length; /* Length of the structure, in bytes. */ > }; > > > > +}; > > > +\end{lstlisting} > > > + > > > +Given that the \field{cap.length} and \field{cap.offset} fields > > > +are only 32 bit, the additional \field{offset_hi} and \field {length_hi} > > > +fields provide the most significant 32 bits of a total 64 bit offset and > > > +length within the bar specified by \field{cap.bar}. \field{id} > > > +uniquely identifies the given shared memory region using a device > > > +specific identifier. > > > > I didn't realize we will ever need so much space. I think I prefer > > moving offset_hi/length_hi to a general virtio_pci_cap64 that others can > > reuse. > > Would we then just rename virtio_pci_shm_cap to virtio_pci_cap64 after > moving the id to virito_pci_cap? yes. and for simplicity we can for now specify that only shmem can be 64 bit. > > > > > > > + > > > +While most capabilities can not be repeated, > > > > I'd drop this part. > > Done. > > > > multiple > > > +VIRTIO_PCI_CAP_SHARED_MEMORY_CFG capabilities are allowed as long > > > +as the \field{id} is unique. > > > + > > > +\devicenormative{\paragraph}{Device-specific configuration}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Shared memory capability} > > > + > > > +The region defined by the combination of the offsets and length > > > +fields > > > > let's do \field{cap.length} \field{cap.offset} etc. > > I've done that as: > The region defined by the combination of the \field {cap.offset}, > \field {cap.offset_hi}, and \field {cap.length}, \field > {cap.length_hi} fields MUST be contained within the declared bar. > > is that right, but the base and hi are in separate structures. > > > >MUST be contained within the declared bar. > > > + > > > +The \field{id} MUST be unique for any one device instance. > > > + > > > \subsubsection{PCI configuration access capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / PCI configuration access capability} > > > > > > The VIRTIO_PCI_CAP_PCI_CFG capability > > > -- > > > 2.20.1 > > > > > > > > > --------------------------------------------------------------------- > > > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > > > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org > -- > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
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