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authorLinus Torvalds <torvalds@linux-foundation.org>2013-09-11 19:09:14 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-11 19:09:14 -0700
commitb3b7568490bb66688ee64f4ab72ec697f4f983c5 (patch)
treee55098d4c05d2169e1934dcdf816e476c2af86f8 /Documentation
parentc2d95729e3094ecdd8c54e856bbe971adbbd7f48 (diff)
parent19e8697ba45e7bcdb04f2adf6110fbf4882863e5 (diff)
downloadlinaro-lsk-b3b7568490bb66688ee64f4ab72ec697f4f983c5.tar.gz
Merge tag 'for-3.12' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf
Pull dma-buf updates from Sumit Semwal: "Yet another small one - dma-buf framework now supports size discovery of the buffer via llseek" * tag 'for-3.12' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf: dma-buf: Expose buffer size to userspace (v2) dma-buf: Check return value of anon_inode_getfile
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/dma-buf-sharing.txt12
1 files changed, 12 insertions, 0 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index e31a2a9d2b0..505e71172ae 100644
--- 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
-------------------