include/uapi/linux/rfkill.h

Source file repositories/reference/linux-study-clean/include/uapi/linux/rfkill.h

File Facts

System
Linux kernel
Corpus path
include/uapi/linux/rfkill.h
Extension
.h
Size
6623 bytes
Lines
192
Domain
Core OS
Bucket
Core Kernel Interface
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

struct rfkill_event {
	__u32 idx;
	__u8  type;
	__u8  op;
	__u8  soft;
	__u8  hard;
} __attribute__((packed));

/**
 * struct rfkill_event_ext - events for userspace on /dev/rfkill
 * @idx: index of dev rfkill
 * @type: type of the rfkill struct
 * @op: operation code
 * @hard: hard state (0/1)
 * @soft: soft state (0/1)
 * @hard_block_reasons: valid if hard is set. One or several reasons from
 *	&enum rfkill_hard_block_reasons.
 *
 * Structure used for userspace communication on /dev/rfkill,
 * used for events from the kernel and control to the kernel.
 *
 * See the extensibility docs below.
 */
struct rfkill_event_ext {
	__u32 idx;
	__u8  type;
	__u8  op;
	__u8  soft;
	__u8  hard;

	/*
	 * older kernels will accept/send only up to this point,
	 * and if extended further up to any chunk marked below
	 */

	__u8  hard_block_reasons;
} __attribute__((packed));

/**
 * DOC: Extensibility
 *
 * Originally, we had planned to allow backward and forward compatible
 * changes by just adding fields at the end of the structure that are
 * then not reported on older kernels on read(), and not written to by
 * older kernels on write(), with the kernel reporting the size it did
 * accept as the result.
 *
 * This would have allowed userspace to detect on read() and write()
 * which kernel structure version it was dealing with, and if was just
 * recompiled it would have gotten the new fields, but obviously not
 * accessed them, but things should've continued to work.
 *
 * Unfortunately, while actually exercising this mechanism to add the
 * hard block reasons field, we found that userspace (notably systemd)
 * did all kinds of fun things not in line with this scheme:
 *
 * 1. treat the (expected) short writes as an error;
 * 2. ask to read sizeof(struct rfkill_event) but then compare the
 *    actual return value to RFKILL_EVENT_SIZE_V1 and treat any
 *    mismatch as an error.
 *
 * As a consequence, just recompiling with a new struct version caused
 * things to no longer work correctly on old and new kernels.
 *
 * Hence, we've rolled back &struct rfkill_event to the original version
 * and added &struct rfkill_event_ext. This effectively reverts to the
 * old behaviour for all userspace, unless it explicitly opts in to the
 * rules outlined here by using the new &struct rfkill_event_ext.
 *
 * Additionally, some other userspace (bluez, g-s-d) was reading with a
 * large size but as streaming reads rather than message-based, or with
 * too strict checks for the returned size. So eventually, we completely
 * reverted this, and extended messages need to be opted in to by using
 * an ioctl:
 *
 *  ioctl(fd, RFKILL_IOCTL_MAX_SIZE, sizeof(struct rfkill_event_ext));
 *
 * Userspace using &struct rfkill_event_ext and the ioctl must adhere to
 * the following rules:
 *
 * 1. accept short writes, optionally using them to detect that it's
 *    running on an older kernel;
 * 2. accept short reads, knowing that this means it's running on an
 *    older kernel;
 * 3. treat reads that are as long as requested as acceptable, not
 *    checking against RFKILL_EVENT_SIZE_V1 or such.
 */
#define RFKILL_EVENT_SIZE_V1	sizeof(struct rfkill_event)

/* ioctl for turning off rfkill-input (if present) */

Annotation

Implementation Notes