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docs: vmcoreinfo: add lockless printk ringbuffer vmcoreinfo

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With the introduction of the lockless printk ringbuffer, the
VMCOREINFO relating to the kernel log buffer was changed. Update the
documentation to match those changes.

Fixes: 896fbe20b4 ("printk: use the lockless ringbuffer")
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200814213316.6394-1-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2020-08-14 23:39:16 +02:06 committed by Petr Mladek
parent 550c10d28d
commit f8ff195ef1
1 changed files with 105 additions and 32 deletions
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137
Documentation/admin-guide/kdump/vmcoreinfo.rst
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@ -184,50 +184,123 @@ from this.
Free areas descriptor. User-space tools use this value to iterate the
free_area ranges. MAX_ORDER is used by the zone buddy allocator.
log_first_idx
-------------
prb
---
Index of the first record stored in the buffer log_buf. Used by
user-space tools to read the strings in the log_buf.
A pointer to the printk ringbuffer (struct printk_ringbuffer). This
may be pointing to the static boot ringbuffer or the dynamically
allocated ringbuffer, depending on when the the core dump occurred.
Used by user-space tools to read the active kernel log buffer.
log_buf
-------
printk_rb_static
----------------
Console output is written to the ring buffer log_buf at index
log_first_idx. Used to get the kernel log.
A pointer to the static boot printk ringbuffer. If @prb has a
different value, this is useful for viewing the initial boot messages,
which may have been overwritten in the dynamically allocated
ringbuffer.
log_buf_len
-----------
log_buf's length.
clear_idx
clear_seq
---------
The index that the next printk() record to read after the last clear
command. It indicates the first record after the last SYSLOG_ACTION
_CLEAR, like issued by 'dmesg -c'. Used by user-space tools to dump
the dmesg log.
The sequence number of the printk() record after the last clear
command. It indicates the first record after the last
SYSLOG_ACTION_CLEAR, like issued by 'dmesg -c'. Used by user-space
tools to dump a subset of the dmesg log.
log_next_idx
------------
printk_ringbuffer
-----------------
The index of the next record to store in the buffer log_buf. Used to
compute the index of the current buffer position.
The size of a printk_ringbuffer structure. This structure contains all
information required for accessing the various components of the
kernel log buffer.
printk_log
----------
(printk_ringbuffer, desc_ring|text_data_ring|dict_data_ring|fail)
-----------------------------------------------------------------
The size of a structure printk_log. Used to compute the size of
messages, and extract dmesg log. It encapsulates header information for
log_buf, such as timestamp, syslog level, etc.
Offsets for the various components of the printk ringbuffer. Used by
user-space tools to view the kernel log buffer without requiring the
declaration of the structure.
(printk_log, ts_nsec|len|text_len|dict_len)
-------------------------------------------
prb_desc_ring
-------------
It represents field offsets in struct printk_log. User space tools
parse it and check whether the values of printk_log's members have been
changed.
The size of the prb_desc_ring structure. This structure contains
information about the set of record descriptors.
(prb_desc_ring, count_bits|descs|head_id|tail_id)
-------------------------------------------------
Offsets for the fields describing the set of record descriptors. Used
by user-space tools to be able to traverse the descriptors without
requiring the declaration of the structure.
prb_desc
--------
The size of the prb_desc structure. This structure contains
information about a single record descriptor.
(prb_desc, info|state_var|text_blk_lpos|dict_blk_lpos)
------------------------------------------------------
Offsets for the fields describing a record descriptors. Used by
user-space tools to be able to read descriptors without requiring
the declaration of the structure.
prb_data_blk_lpos
-----------------
The size of the prb_data_blk_lpos structure. This structure contains
information about where the text or dictionary data (data block) is
located within the respective data ring.
(prb_data_blk_lpos, begin|next)
-------------------------------
Offsets for the fields describing the location of a data block. Used
by user-space tools to be able to locate data blocks without
requiring the declaration of the structure.
printk_info
-----------
The size of the printk_info structure. This structure contains all
the meta-data for a record.
(printk_info, seq|ts_nsec|text_len|dict_len|caller_id)
------------------------------------------------------
Offsets for the fields providing the meta-data for a record. Used by
user-space tools to be able to read the information without requiring
the declaration of the structure.
prb_data_ring
-------------
The size of the prb_data_ring structure. This structure contains
information about a set of data blocks.
(prb_data_ring, size_bits|data|head_lpos|tail_lpos)
---------------------------------------------------
Offsets for the fields describing a set of data blocks. Used by
user-space tools to be able to access the data blocks without
requiring the declaration of the structure.
atomic_long_t
-------------
The size of the atomic_long_t structure. Used by user-space tools to
be able to copy the full structure, regardless of its
architecture-specific implementation.
(atomic_long_t, counter)
------------------------
Offset for the long value of an atomic_long_t variable. Used by
user-space tools to access the long value without requiring the
architecture-specific declaration.
(free_area.free_list, MIGRATE_TYPES)
------------------------------------