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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
| commit | f4cdf7ca9a1fdcca413157df19753f388a5a224e (patch) | |
| tree | 60a31895b2446cd7fa27514e8c2843534a0de0da /Documentation/ABI/testing/dev-kmsg | |
| download | linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.tar.gz linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.zip | |
Merge tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-mediagrafted
Pull media updates from Mauro Carvalho Chehab:
- v4l2-core: added ISP statistics support and per-block validation
- v4l2-core: Allow unknown HDR10 white point and luminance
- New camera sensors: Sony IMX678 and IMX471m, Himax HM1092 IR sensor
- New codec: Milos: VPU v2.0 codec support
- isp driver: gained support for Dreamchip RPPX1 ISP framework
- vsp1 driver: gained support for RZ/T2H and RZ/N2H
- Novalake driver: gained CVS support for new NVL hardware
- dvb-core: fix feed leak on failed DMX_ADD_PID
- several driver fixes, cleanups and minor improvements
* tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (308 commits)
media: ipu-bridge: check all DMI entries when overriding sensor rotation
media: v4l2-async: avoid deleting unlinked ASC entry on link error
media: rzg2l-cru: Align bytesperline to hardware DMA stride requirement
media: intel/ipu6: fix async notifier cleanup leak on parse error
media: staging/ipu7: fix async notifier UAF on probe error path
media: amd: isp4: fix self-deadlock in isp4sd_pwron_and_init() error path
media: amd: isp4: release partial allocations in isp4if_alloc_fw_gpumem()
media: rcar-isp: Fix VSPX reference leaks
media: rcar-isp: Release ISPCORE resources
media: i2c: imx415: Release runtime PM reference on VBLANK error
media: i2c: imx415: Return test pattern write errors
media: renesas: vsp1: Declare index variables in for loop statement
media: renesas: vsp1: Make reset control optional to support platforms without a reset line
media: dt-bindings: media: renesas,vsp1: Document RZ/T2H and RZ/N2H SoCs
media: dt-bindings: media: renesas,fcp: Document RZ/T2H and RZ/N2H SoCs
media: nxp: imx8-isi: Add additional 32-bit RGB format support
media: nxp: imx8-isi: Add 16-bit raw Bayer format support
media: nxp: imx8-isi: Implement per-stream reference counting for multiplexed streams
media: nxp: imx8-isi: Use BIT_ULL() for 64-bit stream masks
media: nxp: imx8-isi: Correct color map between V4L2 and ISI
...
Diffstat (limited to 'Documentation/ABI/testing/dev-kmsg')
| -rw-r--r-- | Documentation/ABI/testing/dev-kmsg | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/dev-kmsg b/Documentation/ABI/testing/dev-kmsg new file mode 100644 index 000000000..a377b6c09 --- /dev/null +++ b/Documentation/ABI/testing/dev-kmsg @@ -0,0 +1,127 @@ +What: /dev/kmsg +Date: Mai 2012 +KernelVersion: 3.5 +Contact: Kay Sievers <kay@vrfy.org> +Description: The /dev/kmsg character device node provides userspace access + to the kernel's printk buffer. + + Injecting messages: + + Every write() to the opened device node places a log entry in + the kernel's printk buffer. + + The logged line can be prefixed with a <N> syslog prefix, which + carries the syslog priority and facility. The single decimal + prefix number is composed of the 3 lowest bits being the syslog + priority and the next 8 bits the syslog facility number. + + If no prefix is given, the priority number is the default kernel + log priority and the facility number is set to LOG_USER (1). It + is not possible to inject messages from userspace with the + facility number LOG_KERN (0), to make sure that the origin of + the messages can always be reliably determined. + + Accessing the buffer: + + Every read() from the opened device node receives one record + of the kernel's printk buffer. + + The first read() directly following an open() always returns + first message in the buffer; there is no kernel-internal + persistent state; many readers can concurrently open the device + and read from it, without affecting other readers. + + Every read() will receive the next available record. If no more + records are available read() will block, or if O_NONBLOCK is + used -EAGAIN returned. + + Messages in the record ring buffer get overwritten as whole, + there are never partial messages received by read(). + + In case messages get overwritten in the circular buffer while + the device is kept open, the next read() will return -EPIPE, + and the seek position be updated to the next available record. + Subsequent reads() will return available records again. + + Unlike the classic syslog() interface, the 64 bit record + sequence numbers allow to calculate the amount of lost + messages, in case the buffer gets overwritten. And they allow + to reconnect to the buffer and reconstruct the read position + if needed, without limiting the interface to a single reader. + + The device supports seek with the following parameters: + + SEEK_SET, 0 + seek to the first entry in the buffer + SEEK_END, 0 + seek after the last entry in the buffer + SEEK_DATA, 0 + seek after the last record available at the time + the last SYSLOG_ACTION_CLEAR was issued. + + Other seek operations or offsets are not supported because of + the special behavior this device has. The device allows to read + or write only whole variable length messages (records) that are + stored in a ring buffer. + + Because of the non-standard behavior also the error values are + non-standard. -ESPIPE is returned for non-zero offset. -EINVAL + is returned for other operations, e.g. SEEK_CUR. This behavior + and values are historical and could not be modified without the + risk of breaking userspace. + + The output format consists of a prefix carrying the syslog + prefix including priority and facility, the 64 bit message + sequence number and the monotonic timestamp in microseconds, + and a flag field. All fields are separated by a ','. + + Future extensions might add more comma separated values before + the terminating ';'. Unknown fields and values should be + gracefully ignored. + + The human readable text string starts directly after the ';' + and is terminated by a '\n'. Untrusted values derived from + hardware or other facilities are printed, therefore + all non-printable characters and '\' itself in the log message + are escaped by "\x00" C-style hex encoding. + + A line starting with ' ', is a continuation line, adding + key/value pairs to the log message, which provide the machine + readable context of the message, for reliable processing in + userspace. + + Example:: + + 7,160,424069,-;pci_root PNP0A03:00: host bridge window [io 0x0000-0x0cf7] (ignored) + SUBSYSTEM=acpi + DEVICE=+acpi:PNP0A03:00 + 6,339,5140900,-;NET: Registered protocol family 10 + 30,340,5690716,-;udevd[80]: starting version 181 + + The DEVICE= key uniquely identifies devices the following way: + + ============ ================= + b12:8 block dev_t + c127:3 char dev_t + n8 netdev ifindex + +sound:card0 subsystem:devname + ============ ================= + + The flags field carries '-' by default. A 'c' indicates a + fragment of a line. Note, that these hints about continuation + lines are not necessarily correct, and the stream could be + interleaved with unrelated messages, but merging the lines in + the output usually produces better human readable results. A + similar logic is used internally when messages are printed to + the console, /proc/kmsg or the syslog() syscall. + + By default, kernel tries to avoid fragments by concatenating + when it can and fragments are rare; however, when extended + console support is enabled, the in-kernel concatenation is + disabled and /dev/kmsg output will contain more fragments. If + the log consumer performs concatenation, the end result + should be the same. In the future, the in-kernel concatenation + may be removed entirely and /dev/kmsg users are recommended to + implement fragment handling. + +Users: dmesg(1), userspace kernel log consumers |
