2019-03-29 14:12:17 +08:00
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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2018-11-01 18:02:22 +08:00
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From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
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Date: Fri, 5 Oct 2018 15:43:02 +0300
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2019-03-29 14:12:17 +08:00
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Subject: [PATCH] stm class: Update documentation to match the new
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2018-11-01 18:02:22 +08:00
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identification rules
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The rules and order of identification of trace sources against the
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"stp-policy" have changed; update the documentation to reflect that.
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Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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Documentation/trace/stm.rst | 36 +++++++++++++++++++++++++++---------
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1 file changed, 27 insertions(+), 9 deletions(-)
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diff --git a/Documentation/trace/stm.rst b/Documentation/trace/stm.rst
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2020-10-27 02:14:06 +08:00
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index 2c22ddb7fd3e..944994fd6368 100644
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2018-11-01 18:02:22 +08:00
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--- a/Documentation/trace/stm.rst
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+++ b/Documentation/trace/stm.rst
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@@ -53,12 +53,30 @@ under "user" directory from the example above and this new rule will
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be used for trace sources with the id string of "user/dummy".
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Trace sources have to open the stm class device's node and write their
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-trace data into its file descriptor. In order to identify themselves
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-to the policy, they need to do a STP_POLICY_ID_SET ioctl on this file
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-descriptor providing their id string. Otherwise, they will be
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-automatically allocated a master/channel pair upon first write to this
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-file descriptor according to the "default" rule of the policy, if such
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-exists.
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+trace data into its file descriptor.
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+
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+In order to find an appropriate policy node for a given trace source,
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+several mechanisms can be used. First, a trace source can explicitly
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+identify itself by calling an STP_POLICY_ID_SET ioctl on the character
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+device's file descriptor, providing their id string, before they write
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+any data there. Secondly, if they chose not to perform the explicit
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+identification (because you may not want to patch existing software
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+to do this), they can just start writing the data, at which point the
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+stm core will try to find a policy node with the name matching the
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+task's name (e.g., "syslogd") and if one exists, it will be used.
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+Thirdly, if the task name can't be found among the policy nodes, the
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+catch-all entry "default" will be used, if it exists. This entry also
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+needs to be created and configured by the system administrator or
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+whatever tools are taking care of the policy configuration. Finally,
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+if all the above steps failed, the write() to an stm file descriptor
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+will return a error (EINVAL).
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+
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+Previously, if no policy nodes were found for a trace source, the stm
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+class would silently fall back to allocating the first available
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+contiguous range of master/channels from the beginning of the device's
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+master/channel range. The new requirement for a policy node to exist
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+will help programmers and sysadmins identify gaps in configuration
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+and have better control over the un-identified sources.
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Some STM devices may allow direct mapping of the channel mmio regions
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to userspace for zero-copy writing. One mappable page (in terms of
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@@ -92,9 +110,9 @@ allocated for the device according to the policy configuration. If
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there's a node in the root of the policy directory that matches the
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stm_source device's name (for example, "console"), this node will be
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used to allocate master and channel numbers. If there's no such policy
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-node, the stm core will pick the first contiguous chunk of channels
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-within the first available master. Note that the node must exist
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-before the stm_source device is connected to its stm device.
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+node, the stm core will use the catch-all entry "default", if one
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+exists. If neither policy nodes exist, the write() to stm_source_link
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+will return an error.
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stm_console
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===========
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--
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2019-04-08 18:08:36 +08:00
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https://clearlinux.org
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2018-11-01 18:02:22 +08:00
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