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Diffstat (limited to 'Documentation/dma-buf-sharing.txt')
| -rw-r--r-- | Documentation/dma-buf-sharing.txt | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt index 0b23261561d2..505e71172ae7 100644 --- a/Documentation/dma-buf-sharing.txt +++ b/Documentation/dma-buf-sharing.txt @@ -321,7 +321,7 @@ Access to a dma_buf from the kernel context involves three steps: When the importer is done accessing the range specified in begin_cpu_access, it needs to announce this to the exporter (to facilitate cache flushing and - unpinning of any pinned resources). The result of of any dma_buf kmap calls + unpinning of any pinned resources). The result of any dma_buf kmap calls after end_cpu_access is undefined. Interface: @@ -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 ------------------- |