diff options
| author | Christopher James Halse Rogers <christopher.halse.rogers@canonical.com> | 2013-09-10 11:36:45 +0530 |
|---|---|---|
| committer | Sumit Semwal <sumit.semwal@linaro.org> | 2013-09-10 11:36:45 +0530 |
| commit | 19e8697ba45e7bcdb04f2adf6110fbf4882863e5 (patch) | |
| tree | 249547a50a16d33e2c3c2dea96a592b2b823dc2b /Documentation/dma-buf-sharing.txt | |
| parent | 9022e24e8946400d53719a761815069c3183e2bd (diff) | |
dma-buf: Expose buffer size to userspace (v2)
Each dma-buf has an associated size and it's reasonable for userspace
to want to know what it is.
Since userspace already has an fd, expose the size using the
size = lseek(fd, SEEK_END, 0); lseek(fd, SEEK_CUR, 0);
idiom.
v2: Added Daniel's sugeested documentation, with minor fixups
Signed-off-by: Christopher James Halse Rogers <christopher.halse.rogers@canonical.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Diffstat (limited to 'Documentation/dma-buf-sharing.txt')
| -rw-r--r-- | Documentation/dma-buf-sharing.txt | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt index e31a2a9d2b07..505e71172ae7 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 ------------------- |