By default we output cgroup id in blktrace. This adds an option to
display cgroup path. Since get cgroup path is a relativly heavy
operation, we don't enable it by default.

with the option enabled, blktrace will output something like this:
dd-1353  [007] d..2   293.015252:   8,0   /test/level  D   R 24 + 8 [dd]
Signed-off-by: NShaohua Li <shli@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently blktrace isn't cgroup aware. blktrace prints out task name of
current context, but the task of current context isn't always in the
cgroup where the BIO comes from. We can't use task name to find out IO
cgroup. For example, Writeback BIOs always comes from flusher thread but
the BIOs are for different blk cgroups. Request could be requeued and
dispatched from completely different tasks. MD/DM are another examples.

This patch tries to fix the gap. We print out cgroup fhandle info in
blktrace. Userspace can use open_by_handle_at() syscall to find the
cgroup by fhandle. Or userspace can use name_to_handle_at() syscall to
find fhandle for a cgroup and use a BPF program to filter out blktrace
for a specific cgroup.

We add a new 'blk_cgroup' trace option for blk tracer. It's default off.
Application which doesn't know the new option isn't affected.  When it's
on, we output fhandle info right after blk_io_trace with an extra bit
set in event action. So from application point of view, blktrace with
the option will output new actions.

I didn't change blk trace event yet, since I'm not sure if changing the
trace event output is an ABI issue. If not, I'll do it later.
Acked-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: NShaohua Li <shli@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Replace bi_error with a new bi_status to allow for a clear conversion.
Note that device mapper overloaded bi_error with a private value, which
we'll have to keep arround at least for now and thus propagate to a
proper blk_status_t value.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

sscanf is a very poor way to parse integer. For example, I input
"discard" for act_mask, it gets 0xd and completely messes up. Using
correct API to do integer parse.

This patch also makes attributes accept any base of integer.
Signed-off-by: NShaohua Li <shli@fb.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBart Van Assche <Bart.VanAssche@sandisk.com>
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

We may already have a directory to put the blktrace stuff in if

1. The disk uses blk-mq
2. CONFIG_BLK_DEBUG_FS is enabled
3. We are tracing the whole disk and not a partition

Instead of hardcoding this very specific case, let's use the new
debugfs_lookup(). If the directory exists, we use it, otherwise we
create one and clean it up later.

Fixes: 07e4fead ("blk-mq: create debugfs directory tree")
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

When I added the blk-mq debugging information to debugfs, I didn't
notice that blktrace also creates a "block" directory in debugfs. Make
them use the same dentry, now created in the core block code. Based on a
patch from Jens.
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This isn't used outside of blktrace.c anymore.

Fixes: 62c2a7d9 ("block: push BKL into blktrace ioctls")
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This can be used to check for fs vs non-fs requests and basically
removes all knowledge of BLOCK_PC specific from the block layer,
as well as preparing for removing the cmd_type field in struct request.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

A couple tweaks to the tracing code:

 - trace the request size for all requests
 - trace request sector and nr_sectors only for fs requests, enforced by
   helpers
 - drop SCSI CDB tracing - we have SCSI tracing for this and are going
   to me the CDB out of the generic struct request soon.

With this the tracing code stops to know about BLOCK_PC requests entirely,
it's just FS vs passthrough requests now, where the latter includes any
driver-private requests.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Now that we don't need the common flags to overflow outside the range
of a 32-bit type we can encode them the same way for both the bio and
request fields.  This in addition allows us to place the operation
first (and make some room for more ops while we're at it) and to
stop having to shift around the operation values.

In addition this allows passing around only one value in the block layer
instead of two (and eventuall also in the file systems, but we can do
that later) and thus clean up a lot of code.

Last but not least this allows decreasing the size of the cmd_flags
field in struct request to 32-bits.  Various functions passing this
value could also be updated, but I'd like to avoid the churn for now.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Commit 288dab8a ("block: add a separate operation type for secure
erase") split REQ_OP_SECURE_ERASE from REQ_OP_DISCARD without considering
all the places REQ_OP_DISCARD was being used to mean either. Fix those.
Signed-off-by: NAdrian Hunter <adrian.hunter@intel.com>
Fixes: 288dab8a ("block: add a separate operation type for secure erase")
Signed-off-by: NJens Axboe <axboe@fb.com>

Since commit 63a4cc24, bio->bi_rw contains flags in the lower
portion and the op code in the higher portions. This means that
old code that relies on manually setting bi_rw is most likely
going to be broken. Instead of letting that brokeness linger,
rename the member, to force old and out-of-tree code to break
at compile time instead of at runtime.

No intended functional changes in this commit.
Signed-off-by: NJens Axboe <axboe@fb.com>

The blktrace code stores the current time in a 32-bit word in its
user interface. This is a bad idea because 32-bit seconds overflow
at some point.

We probably have until 2106 before this one overflows, as it seems
to use an 'unsigned' variable, but we should confirm that user
space treats it the same way.

Aside from this, we want to stop using 'struct timespec' here,
so I'm adding a comment about the overflow and change the code
to use timespec64 instead to make the loss of range more obvious.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Instead of overloading the discard support with the REQ_SECURE flag.
Use the opportunity to rename the queue flag as well, and remove the
dead checks for this flag in the RAID 1 and RAID 10 drivers that don't
claim support for secure erase.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

To avoid confusion between REQ_OP_FLUSH, which is handled by
request_fn drivers, and upper layers requesting the block layer
perform a flush sequence along with possibly a WRITE, this patch
renames REQ_FLUSH to REQ_PREFLUSH.
Signed-off-by: NMike Christie <mchristi@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This adds a REQ_OP_FLUSH operation that is sent to request_fn
based drivers by the block layer's flush code, instead of
sending requests with the request->cmd_flags REQ_FLUSH bit set.
Signed-off-by: NMike Christie <mchristi@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Have blktrace use the req/bio op accessor to get the REQ_OP.
Signed-off-by: NMike Christie <mchristi@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

BLK_TC_NOTIFY is missed in mask_maps, so we can't print out notify or
set mask with 'notify' name.
Signed-off-by: NShaohua Li <shli@fb.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

commit f4a1d08c introduces a regression. Originally for
BLK_TN_MESSAGE, we add message in trace and return. The commit ignores
the early return and add garbage info.
Signed-off-by: NShaohua Li <shli@fb.com>
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Use the more common logging method with the eventual goal of removing
pr_warning altogether.

Miscellanea:

 - Realign arguments
 - Coalesce formats
 - Add missing space between a few coalesced formats
Signed-off-by: NJoe Perches <joe@perches.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>	[kernel/power/suspend.c]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

A _lot_ of ->write() instances were open-coding it; some are
converted to memdup_user_nul(), a lot more remain...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

This is really about simplifying the double xchg patterns into
a single cmpxchg, with the same logic. Other than the immediate
cleanup, there are some subtleties this change deals with:

(i) While the load of the old bt is fully ordered wrt everything,
ie:

        old_bt = xchg(&q->blk_trace, bt);             [barrier]
        if (old_bt)
	     (void) xchg(&q->blk_trace, old_bt);    [barrier]

blk_trace could still be changed between the xchg and the old_bt
load. Note that this description is merely theoretical and afaict
very small, but doing everything in a single context with cmpxchg
closes this potential race.

(ii) Ordering guarantees are obviously kept with cmpxchg.

(iii) Gets rid of the hacky-by-nature (void)xchg pattern.
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
eviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

In preparation to make trace options per instance, the global trace_flags
needs to be moved from being a global variable to a field within the trace
instance trace_array structure.

There's still more work to do, as there's some functions that use
trace_flags without passing in a way to get to the current_trace array. For
those, the global_trace is used directly (from trace.c). This includes
setting and clearing the trace_flags. This means that when a new instance is
created, it just gets the trace_flags of the global_trace and will not be
able to modify them. Depending on the functions that have access to the
trace_array, the flags of an instance may not affect parts of its trace,
where the global_trace is used. These will be fixed in future changes.
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

In preparation for having trace options be per instance, the trace_array
needs to be passed to the trace_buffer_unlock_commit(). The
trace_event_buffer_lock_reserve() already passes in the trace_event_file
where the trace_array can be derived from.

Also added a "__init" to the boot up test event plus function tracing
function function_test_events_call().
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Currently we have two different ways to signal an I/O error on a BIO:

 (1) by clearing the BIO_UPTODATE flag
 (2) by returning a Linux errno value to the bi_end_io callback

The first one has the drawback of only communicating a single possible
error (-EIO), and the second one has the drawback of not beeing persistent
when bios are queued up, and are not passed along from child to parent
bio in the ever more popular chaining scenario.  Having both mechanisms
available has the additional drawback of utterly confusing driver authors
and introducing bugs where various I/O submitters only deal with one of
them, and the others have to add boilerplate code to deal with both kinds
of error returns.

So add a new bi_error field to store an errno value directly in struct
bio and remove the existing mechanisms to clean all this up.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NNeilBrown <neilb@suse.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Part of the disassembly of do_blk_trace_setup:

    231b:       e8 00 00 00 00          callq  2320 <do_blk_trace_setup+0x50>
                        231c: R_X86_64_PC32     strlen+0xfffffffffffffffc
    2320:       eb 0a                   jmp    232c <do_blk_trace_setup+0x5c>
    2322:       66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
    2328:       48 83 c3 01             add    $0x1,%rbx
    232c:       48 39 d8                cmp    %rbx,%rax
    232f:       76 47                   jbe    2378 <do_blk_trace_setup+0xa8>
    2331:       41 80 3c 1c 2f          cmpb   $0x2f,(%r12,%rbx,1)
    2336:       75 f0                   jne    2328 <do_blk_trace_setup+0x58>
    2338:       41 c6 04 1c 5f          movb   $0x5f,(%r12,%rbx,1)
    233d:       4c 89 e7                mov    %r12,%rdi
    2340:       e8 00 00 00 00          callq  2345 <do_blk_trace_setup+0x75>
                        2341: R_X86_64_PC32     strlen+0xfffffffffffffffc
    2345:       eb e1                   jmp    2328 <do_blk_trace_setup+0x58>

Yep, that's right: gcc isn't smart enough to realize that replacing '/' by
'_' cannot change the strlen(), so we call it again and again (at least
when a '/' is found).  Even if gcc were that smart, this construction
would still loop over the string twice, once for the initial strlen() call
and then the open-coded loop.

Let's simply use strreplace() instead.
Signed-off-by: NRasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Liked-by: NJens Axboe <axboe@fb.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The name "ftrace" really refers to the function hook infrastructure. It
is not about the trace_events. The functions (un)register_ftrace_event() is
really about trace_events, and the name should be register_trace_event()
instead.

Also renamed ftrace_event_reg() to trace_event_reg() for the same reason.
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Currently, blktrace can be started/stopped via its ioctl-based interface
(used by the userspace blktrace tool) or via its ftrace interface. The
function blk_trace_remove_queue(), called each time an "enable" tunable
of the ftrace interface transitions to zero, removes the trace from the
running list, even if no function from the sysfs interface adds it to
such a list. This leads to a null pointer dereference.  This commit
changes the blk_trace_remove_queue() function so that it does not remove
the blk_trace from the running list.

v2:
    - Now the patch removes the invocation of list_del() instead of
      adding an useless if branch, as suggested by Namhyung Kim.
Signed-off-by: NArianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Checking the return code of every trace_seq_printf() operation and having
to return early if it overflowed makes the code messy.

Using the new trace_seq_has_overflowed() and trace_handle_return() functions
allows us to clean up the code.

In the future, trace_seq_printf() and friends will be turning into void
functions and not returning a value. The trace_seq_has_overflowed() is to
be used instead. This cleanup allows that change to take place.

Cc: Jens Axboe <axboe@fb.com>
Reviewed-by: NPetr Mladek <pmladek@suse.cz>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

trace_block_rq_complete does not take into account that request can
be partially completed, so we can get the following incorrect output
of blkparser:

  C   R 232 + 240 [0]
  C   R 240 + 232 [0]
  C   R 248 + 224 [0]
  C   R 256 + 216 [0]

but should be:

  C   R 232 + 8 [0]
  C   R 240 + 8 [0]
  C   R 248 + 8 [0]
  C   R 256 + 8 [0]

Also, the whole output summary statistics of completed requests and
final throughput will be incorrect.

This patch takes into account real completion size of the request and
fixes wrong completion accounting.
Signed-off-by: NRoman Pen <r.peniaev@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@redhat.com>
CC: linux-kernel@vger.kernel.org
Cc: stable@kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

As options (flags) may affect instances instead of being global
the set_flag() callbacks need to receive the trace_array descriptor
of the instance they will be modifying.
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Immutable biovecs are going to require an explicit iterator. To
implement immutable bvecs, a later patch is going to add a bi_bvec_done
member to this struct; for now, this patch effectively just renames
things.
Signed-off-by: NKent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: "Ed L. Cashin" <ecashin@coraid.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Lars Ellenberg <drbd-dev@lists.linbit.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Yehuda Sadeh <yehuda@inktank.com>
Cc: Sage Weil <sage@inktank.com>
Cc: Alex Elder <elder@inktank.com>
Cc: ceph-devel@vger.kernel.org
Cc: Joshua Morris <josh.h.morris@us.ibm.com>
Cc: Philip Kelleher <pjk1939@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Neil Brown <neilb@suse.de>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: dm-devel@redhat.com
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux390@de.ibm.com
Cc: Boaz Harrosh <bharrosh@panasas.com>
Cc: Benny Halevy <bhalevy@tonian.com>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Chris Mason <chris.mason@fusionio.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Jaegeuk Kim <jaegeuk.kim@samsung.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Dave Kleikamp <shaggy@kernel.org>
Cc: Joern Engel <joern@logfs.org>
Cc: Prasad Joshi <prasadjoshi.linux@gmail.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Ben Myers <bpm@sgi.com>
Cc: xfs@oss.sgi.com
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Guo Chao <yan@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Cc: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchand@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Peng Tao <tao.peng@emc.com>
Cc: Andy Adamson <andros@netapp.com>
Cc: fanchaoting <fanchaoting@cn.fujitsu.com>
Cc: Jie Liu <jeff.liu@oracle.com>
Cc: Sunil Mushran <sunil.mushran@gmail.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Pankaj Kumar <pankaj.km@samsung.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Mel Gorman <mgorman@suse.de>6

do_blk_trace_setup() will fully initialize 'buts.name', so can remove
the related memcpy(). And also use BLKTRACE_BDEV_SIZE and ARRAY_SIZE
instead of hard code number '32'.
Signed-off-by: NChen Gang <gang.chen@asianux.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently each task sends BLK_TN_PROCESS event to the first traced
device it interacts with after a new trace is started. When there are
several traced devices and the task accesses more devices, this logic
can result in BLK_TN_PROCESS being sent several times to some devices
while it is never sent to other devices. Thus blkparse doesn't display
command name when parsing some blktrace files.

Fix the problem by sending BLK_TN_PROCESS event to all traced devices
when a task interacts with any of them.
Signed-off-by: NJan Kara <jack@suse.cz>
Review-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This reverts commit 3a366e61.

Wanlong Gao reports that it causes a kernel panic on his machine several
minutes after boot. Reverting it removes the panic.

Jens says:
 "It's not quite clear why that is yet, so I think we should just revert
  the commit for 3.9 final (which I'm assuming is pretty close).

  The wifi is crap at the LSF hotel, so sending this email instead of
  queueing up a revert and pull request."
Reported-by: NWanlong Gao <gaowanlong@cn.fujitsu.com>
Requested-by: NJens Axboe <axboe@kernel.dk>
Cc: Tejun Heo <tj@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Exported so it can be used by bcache's tracepoints
Signed-off-by: NKent Overstreet <koverstreet@google.com>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@redhat.com>

Currently, the way the latency tracers and snapshot feature works
is to have a separate trace_array called "max_tr" that holds the
snapshot buffer. For latency tracers, this snapshot buffer is used
to swap the running buffer with this buffer to save the current max
latency.

The only items needed for the max_tr is really just a copy of the buffer
itself, the per_cpu data pointers, the time_start timestamp that states
when the max latency was triggered, and the cpu that the max latency
was triggered on. All other fields in trace_array are unused by the
max_tr, making the max_tr mostly bloat.

This change removes the max_tr completely, and adds a new structure
called trace_buffer, that holds the buffer pointer, the per_cpu data
pointers, the time_start timestamp, and the cpu where the latency occurred.

The trace_array, now has two trace_buffers, one for the normal trace and
one for the max trace or snapshot. By doing this, not only do we remove
the bloat from the max_trace but the instances of traces can now use
their own snapshot feature and not have just the top level global_trace have
the snapshot feature and latency tracers for itself.
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

typeof(&buffer) is a pointer to array of 1024 char, or char (*)[1024].
But, typeof(&buffer[0]) is a pointer to char which match the return type of get_trace_buf().
As well-known, the value of &buffer is equal to &buffer[0].
so return this_cpu_ptr(&percpu_buffer->buffer[0]) can avoid type cast.

Link: http://lkml.kernel.org/r/50A1A800.3020102@gmail.comReviewed-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NShan Wei <davidshan@tencent.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>