Merge branch 'for-3.14-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

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

diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index e31a2a9d2b075e9dda835218b63fd103cb91d6fa..505e71172ae7f17814cc87a5a18d489cd8cdf6a9 100644 (file)
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -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
 -------------------