Documentation/userspace-api/media/dvb/dmx-querybuf.rst
Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/dvb/dmx-querybuf.rst
File Facts
- System
- Linux kernel
- Corpus path
Documentation/userspace-api/media/dvb/dmx-querybuf.rst- Extension
.rst- Size
- 1725 bytes
- Lines
- 65
- Domain
- Support Tooling And Documentation
- Bucket
- Documentation
- Inferred role
- Support Tooling And Documentation: documentation
- Status
- atlas-only
Why This File Exists
Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
- Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
- Defines or uses C structs; map object ownership, embedded links, reference counts, and lock ownership.
Dependency Surface
- No C-style include directives detected by the generator.
Detected Declarations
- No top-level syscall, struct, function, initcall, or export declaration detected by the generator.
Annotated Snippet
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: DTV.dmx
.. _DMX_QUERYBUF:
******************
ioctl DMX_QUERYBUF
******************
Name
====
DMX_QUERYBUF - Query the status of a buffer
.. warning:: this API is still experimental
Synopsis
========
.. c:macro:: DMX_QUERYBUF
``int ioctl(int fd, DMX_QUERYBUF, struct dvb_buffer *argp)``
Arguments
=========
``fd``
File descriptor returned by :c:func:`open()`.
``argp``
Pointer to struct :c:type:`dvb_buffer`.
Description
===========
This ioctl is part of the mmap streaming I/O method. It can
be used to query the status of a buffer at any time after buffers have
been allocated with the :ref:`DMX_REQBUFS` ioctl.
Applications set the ``index`` field. Valid index numbers range from zero
to the number of buffers allocated with :ref:`DMX_REQBUFS`
(struct :c:type:`dvb_requestbuffers` ``count``) minus one.
After calling :ref:`DMX_QUERYBUF` with a pointer to this structure,
drivers return an error code or fill the rest of the structure.
On success, the ``offset`` will contain the offset of the buffer from the
start of the device memory, the ``length`` field its size, and the
``bytesused`` the number of bytes occupied by data in the buffer (payload).
Return Value
============
On success 0 is returned, the ``offset`` will contain the offset of the
buffer from the start of the device memory, the ``length`` field its size,
and the ``bytesused`` the number of bytes occupied by data in the buffer
(payload).
On error it returns -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.
EINVAL
The ``index`` is out of bounds.Annotation
- Atlas domain: Support Tooling And Documentation / Documentation.
- Implementation status: atlas-only.
Implementation Notes
- This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
- Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
- Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.