rework the buffer management style + talk about dma-buf

1 files changed, 53 insertions, 7 deletions

diff --git a/linuxgraphicsdrivers.lyx b/linuxgraphicsdrivers.lyx
index f2c148a..3826847 100644
--- a/linuxgraphicsdrivers.lyx
+++ b/linuxgraphicsdrivers.lyx
@@ -5580,7 +5580,7 @@ To prevent access to arbitrary GPU memory, the command submission ioctl
 \end_layout
 
 \begin_layout Subsubsection
-Buffer management
+GEM Buffer management
 \end_layout
 
 \begin_layout Standard
@@ -5602,7 +5602,7 @@ ent libdrm calls to manage your buffers.
  However, the general outline of the interface remains fairly constant.
 \end_layout
 
-\begin_layout Paragraph*
+\begin_layout Subsubsection*
 
 \lang english
 Object Allocation & Destruction
@@ -5615,7 +5615,7 @@ Object allocation is done by calling the GEM_CREATE function.
  This handle will be used later on as a buffer identifier.
 \end_layout
 
-\begin_layout Paragraph*
+\begin_layout Subsubsection*
 
 \lang english
 Reading and writing from/to a buffer object
@@ -5638,7 +5638,7 @@ mapping the BO : it is possible for the userspace to map the BO in his memory
  It then returns the address of the BO in the user's virtual address space.
 \end_layout
 
-\begin_layout Paragraph*
+\begin_layout Subsubsection*
 Sharing buffer objects between applications
 \end_layout
 
@@ -5689,16 +5689,62 @@ the authenticated client calls drm_authmagic to authenticate the cookie
  and thus, the original client
 \end_layout
 
-\begin_layout Paragraph*
+\begin_layout Subsubsection*
+Learning more about GEM
+\end_layout
+
+\begin_layout Standard
+The best documentation for GEM is the source code the drivers exposing it
+ (libdrm for the userspace, the drm driver for the kernelspace).
+ However, it is worth reading the initial proposal called 
+\begin_inset CommandInset href
+LatexCommand href
+name "GEM - the Graphics Execution Manager"
+target "https://lwn.net/Articles/283798/"
+
+\end_inset
+
+ from Intel.
+ 
+\end_layout
+
+\begin_layout Subsubsection
+
+\lang english
+DMA-Buf : Sharing buffer objects between drivers
+\end_layout
+
+\begin_layout Standard
+
+\lang english
+DMA-Buf is a driver-independent buffer-sharing mechanism for clients.
+\end_layout
+
+\begin_layout Standard
 
 \lang english
-Sharing buffer objects between drivers
+Contrarily to GEM buffer sharing, a fd is returned to the client willing
+ to export a buffer.
+ It is then the client's responsability to export this fd to the other clients
+ using a UNIX socket as explained by this 
+\begin_inset CommandInset href
+LatexCommand href
+name "email from Greg A. Woods"
+target "http://archives.neohapsis.com/archives/postfix/2000-09/1476.html"
+
+\end_inset
+
+.
+ This sharing solution is more secure since clients cannot access to buffers
+ unless explicitely allowed by the exporter contrarily to GEM where names
+ are guessable.
 \end_layout
 
 \begin_layout Standard
 
 \lang english
-dma_buf
+For more information, look at /Documentation/dma-buf-sharing.txt in your
+ kernel tree.
 \end_layout
 
 \begin_layout Section