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Videobuf2 presently does not allow VIDIOC_REQBUFS to destroy outstanding buffers if the queue is of type V4L2_MEMORY_MMAP, and if the buffers are considered "in use". This is different behavior than for other memory types and prevents us from deallocating buffers in following two cases: 1) There are outstanding mmap()ed views on the buffer. However even if we put the buffer in reqbufs(0), there will be remaining references, due to vma .open/close() adjusting vb2 buffer refcount appropriately. This means that the buffer will be in fact freed only when the last mmap()ed view is unmapped. 2) Buffer has been exported as a DMABUF. Refcount of the vb2 buffer is managed properly by VB2 DMABUF ops, i.e. incremented on DMABUF get and decremented on DMABUF release. This means that the buffer will be alive until all importers release it. Considering both cases above, there does not seem to be any need to prevent reqbufs(0) operation, because buffer lifetime is already properly managed by both mmap() and DMABUF code paths. Let's remove it and allow userspace freeing the queue (and potentially allocating a new one) even though old buffers might be still in processing. To let userspace know that the kernel now supports orphaning buffers that are still in use, add a new V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS to be set by reqbufs and create_bufs. [p.zabel@pengutronix.de: added V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS, updated documentation, and added back debug message] Signed-off-by: John Sheu <sheu@chromium.org> Reviewed-by: Pawel Osciak <posciak@chromium.org> Signed-off-by: Tomasz Figa <tfiga@chromium.org> Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de> Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> [hverkuil-cisco@xs4all.nl: added V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS ref] Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.