Merge tag 'printk-for-5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/printk...

[linux-block.git] / Documentation / ABI / testing / dev-kmsg

diff --git a/Documentation/ABI/testing/dev-kmsg b/Documentation/ABI/testing/dev-kmsg
index f307506eb54ce9a44601ba37ba798314049da762..3c0bb76e3417e7ce402378e849d4ee7858ae019c 100644 (file)
--- a/Documentation/ABI/testing/dev-kmsg
+++ b/Documentation/ABI/testing/dev-kmsg
@@ -56,6 +56,17 @@ Description: The /dev/kmsg character device node provides userspace access
                  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,