PM / Documentation: Update copyright in suspend-and-cpuhotplug.txt

[cascardo/linux.git] / Documentation / dma-buf-sharing.txt

diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index e31a2a9..67a4087 100644 (file)
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -66,7 +66,7 @@ The dma_buf buffer sharing API usage contains the following steps:
 
    Exporting modules which do not wish to provide any specific name may use the
    helper define 'dma_buf_export()', with the same arguments as above, but
-   without the last argument; a __FILE__ pre-processor directive will be
+   without the last argument; a KBUILD_MODNAME pre-processor directive will be
    inserted in place of 'exp_name' instead.
 
 2. Userspace gets a handle to pass around to potential buffer-users
@@ -217,7 +217,7 @@ NOTES:
     and then allow further {map,unmap}_dma_buf operations from any buffer-user
     from the migrated backing-storage.
 
-   If the exporter cannot fulfil the backing-storage constraints of the new
+   If the exporter cannot fulfill the backing-storage constraints of the new
    buffer-user device as requested, dma_buf_attach() would return an error to
    denote non-compatibility of the new buffer-sharing request with the current
    buffer.
@@ -352,7 +352,7 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
 
    No special interfaces, userspace simply calls mmap on the dma-buf fd.
 
-2. Supporting existing mmap interfaces in exporters
+2. Supporting existing mmap interfaces in importers
 
    Similar to the motivation for kernel cpu access it is again important that
    the userspace code of a given importing subsystem can use the same interfaces
@@ -407,6 +407,18 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
    interesting ways depending upong the exporter (if userspace starts depending
    upon this implicit synchronization).
 
+Other Interfaces Exposed to Userspace on the dma-buf FD
+------------------------------------------------------
+
+- Since kernel 3.12 the dma-buf FD supports the llseek system call, but only
+  with offset=0 and whence=SEEK_END|SEEK_SET. SEEK_SET is supported to allow
+  the usual size discover pattern size = SEEK_END(0); SEEK_SET(0). Every other
+  llseek operation will report -EINVAL.
+
+  If llseek on dma-buf FDs isn't support the kernel will report -ESPIPE for all
+  cases. Userspace can use this to detect support for discovering the dma-buf
+  size using llseek.
+
 Miscellaneous notes
 -------------------