From 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2023 18:24:12 -0800 Subject: Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ... --- .../userspace-api/media/v4l/func-read.rst | 130 +++++++++++++++++++++ 1 file changed, 130 insertions(+) create mode 100644 Documentation/userspace-api/media/v4l/func-read.rst (limited to 'Documentation/userspace-api/media/v4l/func-read.rst') diff --git a/Documentation/userspace-api/media/v4l/func-read.rst b/Documentation/userspace-api/media/v4l/func-read.rst new file mode 100644 index 000000000..e6f6ac4be --- /dev/null +++ b/Documentation/userspace-api/media/v4l/func-read.rst @@ -0,0 +1,130 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _func-read: + +*********** +V4L2 read() +*********** + +Name +==== + +v4l2-read - Read from a V4L2 device + +Synopsis +======== + +.. code-block:: c + + #include + +.. c:function:: ssize_t read( int fd, void *buf, size_t count ) + +Arguments +========= + +``fd`` + File descriptor returned by :c:func:`open()`. + +``buf`` + Buffer to be filled + +``count`` + Max number of bytes to read + +Description +=========== + +:c:func:`read()` attempts to read up to ``count`` bytes from file +descriptor ``fd`` into the buffer starting at ``buf``. The layout of the +data in the buffer is discussed in the respective device interface +section, see ##. If ``count`` is zero, :c:func:`read()` returns zero +and has no other results. If ``count`` is greater than ``SSIZE_MAX``, +the result is unspecified. Regardless of the ``count`` value each +:c:func:`read()` call will provide at most one frame (two fields) +worth of data. + +By default :c:func:`read()` blocks until data becomes available. When +the ``O_NONBLOCK`` flag was given to the :c:func:`open()` +function it returns immediately with an ``EAGAIN`` error code when no data +is available. The :c:func:`select()` or +:c:func:`poll()` functions can always be used to suspend +execution until data becomes available. All drivers supporting the +:c:func:`read()` function must also support :c:func:`select()` and +:c:func:`poll()`. + +Drivers can implement read functionality in different ways, using a +single or multiple buffers and discarding the oldest or newest frames +once the internal buffers are filled. + +:c:func:`read()` never returns a "snapshot" of a buffer being filled. +Using a single buffer the driver will stop capturing when the +application starts reading the buffer until the read is finished. Thus +only the period of the vertical blanking interval is available for +reading, or the capture rate must fall below the nominal frame rate of +the video standard. + +The behavior of :c:func:`read()` when called during the active picture +period or the vertical blanking separating the top and bottom field +depends on the discarding policy. A driver discarding the oldest frames +keeps capturing into an internal buffer, continuously overwriting the +previously, not read frame, and returns the frame being received at the +time of the :c:func:`read()` call as soon as it is complete. + +A driver discarding the newest frames stops capturing until the next +:c:func:`read()` call. The frame being received at :c:func:`read()` +time is discarded, returning the following frame instead. Again this +implies a reduction of the capture rate to one half or less of the +nominal frame rate. An example of this model is the video read mode of +the bttv driver, initiating a DMA to user memory when :c:func:`read()` +is called and returning when the DMA finished. + +In the multiple buffer model drivers maintain a ring of internal +buffers, automatically advancing to the next free buffer. This allows +continuous capturing when the application can empty the buffers fast +enough. Again, the behavior when the driver runs out of free buffers +depends on the discarding policy. + +Applications can get and set the number of buffers used internally by +the driver with the :ref:`VIDIOC_G_PARM ` and +:ref:`VIDIOC_S_PARM ` ioctls. They are optional, +however. The discarding policy is not reported and cannot be changed. +For minimum requirements see :ref:`devices`. + +Return Value +============ + +On success, the number of bytes read is returned. It is not an error if +this number is smaller than the number of bytes requested, or the amount +of data required for one frame. This may happen for example because +:c:func:`read()` was interrupted by a signal. On error, -1 is +returned, and the ``errno`` variable is set appropriately. In this case +the next read will start at the beginning of a new frame. Possible error +codes are: + +EAGAIN + Non-blocking I/O has been selected using O_NONBLOCK and no data was + immediately available for reading. + +EBADF + ``fd`` is not a valid file descriptor or is not open for reading, or + the process already has the maximum number of files open. + +EBUSY + The driver does not support multiple read streams and the device is + already in use. + +EFAULT + ``buf`` references an inaccessible memory area. + +EINTR + The call was interrupted by a signal before any data was read. + +EIO + I/O error. This indicates some hardware problem or a failure to + communicate with a remote device (USB camera etc.). + +EINVAL + The :c:func:`read()` function is not supported by this driver, not + on this device, or generally not on this type of device. -- cgit v1.2.3