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Diffstat (limited to 'Documentation/ABI/testing/dev-kmsg')
| -rw-r--r-- | Documentation/ABI/testing/dev-kmsg | 90 |
1 files changed, 0 insertions, 90 deletions
diff --git a/Documentation/ABI/testing/dev-kmsg b/Documentation/ABI/testing/dev-kmsg deleted file mode 100644 index 281ecc5..0000000 --- a/Documentation/ABI/testing/dev-kmsg +++ /dev/null @@ -1,90 +0,0 @@ -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 higher 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. - - 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. - The values are separated by a ','. Future extensions might - add more comma separated values before the terminating ';'. - Unknown 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 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 - -Users: dmesg(1), userspace kernel log consumers |