[PATCH v5 2/5] pci: Define id field

From: "Dr. David Alan Gilbert" <>

For the virtio-fs device we require multiple large shared memory
regions.  Differentiate these by an 'id' field in the base capability.

Signed-off-by: Dr. David Alan Gilbert <>
---
 content.tex | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/content.tex b/content.tex
index 6433226..41926c0 100644
--- a/content.tex
+++ b/content.tex
@@ -651,7 +651,8 @@ \subsection{Virtio Structure PCI Capabilities}\label{sec:Virtio Transport Option
         u8 cap_len;     /* Generic PCI field: capability length */
         u8 cfg_type;    /* Identifies the structure. */
         u8 bar;         /* Where to find it. */
-        u8 padding[3];  /* Pad to full dword. */
+        u8 id;          /* Multiple capabilities of the same type */
+        u8 padding[2];  /* Pad to full dword. */
         le32 offset;    /* Offset within bar. */
         le32 length;    /* Length of the structure, in bytes. */
 };
@@ -716,6 +717,11 @@ \subsection{Virtio Structure PCI Capabilities}\label{sec:Virtio Transport Option
 
         Any other value is reserved for future use.
 
+\item[\field{id}]
+        Multiple capabilities of the same type can exist as long
+        as they each have a unique \field{id}.  The specific
+        meaning of the field is different for each device type.
+
 \item[\field{offset}]
         indicates where the structure begins relative to the base address associated
         with the BAR.  The alignment requirements of \field{offset} are indicated
-- 
2.21.0