The functions that assign the contents for the ftrace events are
defined by the TRACE_EVENT() macros. Each event has its own unique
way to assign data to its buffer. When you have over 500 events,
that means there's 500 functions assigning data uniquely for each
event (not really that many, as DECLARE_EVENT_CLASS() and multiple
DEFINE_EVENT()s will only need a single function).

By making helper functions in the core kernel to do some of the work
instead, we can shrink the size of the kernel down a bit.

With a kernel configured with 502 events, the change in size was:

   text    data     bss     dec     hex filename
12987390        1913504 9785344 24686238        178ae9e /tmp/vmlinux
12959102        1913504 9785344 24657950        178401e /tmp/vmlinux.patched

That's a total of 28288 bytes, which comes down to 56 bytes per event.

Link: http://lkml.kernel.org/r/20120810034708.370808175@goodmis.orgSigned-off-by: Steven Rostedt <rostedt@goodmis.org>

The code that shows array fields for events is defined for all events.
This can add up quite a bit when you have over 500 events.

By making helper functions in the core kernel to do the work
instead, we can shrink the size of the kernel down a bit.

With a kernel configured with 502 events, the change in size was:

   text    data     bss     dec     hex filename
12990946        1913568 9785344 24689858        178bcc2 /tmp/vmlinux
12987390        1913504 9785344 24686238        178ae9e /tmp/vmlinux.patched

That's a total of 3556 bytes, which comes down to 7 bytes per event.
Although it's not much, this code is just called at initialization of
the events.

Link: http://lkml.kernel.org/r/20120810034708.084036335@goodmis.orgSigned-off-by: Steven Rostedt <rostedt@goodmis.org>

The code for trace events to format the raw recorded event data
into human readable format in the 'trace' file is repeated for every
event in the system. When you have over 500 events, this can add up
quite a bit.

By making helper functions in the core kernel to do the work
instead, we can shrink the size of the kernel down a bit.

With a kernel configured with 502 events, the change in size was:

   text    data     bss     dec     hex filename
12991007        1913568 9785344 24689919        178bcff /tmp/vmlinux.orig
12990946        1913568 9785344 24689858        178bcc2 /tmp/vmlinux.patched

Note, this version does not save as much as the version of this patch
I had a few years ago. That is because in the mean time, commit
f71130de ("tracing: Add a helper function for event print functions")
did a lot of the work my original patch did. But this change helps
slightly, and is part of a larger clean up to reduce the size much further.

Link: http://lkml.kernel.org/r/20120810034707.378538034@goodmis.org

Cc: Li Zefan <lizefan@huawei.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Having ftrace_write() return -EPERM on failure, as that's what the callers
return, then we can clean up the code a bit. That is, instead of:

  if (ftrace_write(...))
     return -EPERM;
  return 0;

or

  if (ftrace_write(...)) {
     ret = -EPERM;
     goto_out;
  }

We can instead have:

  return ftrace_write(...);

or

  ret = ftrace_write(...);
  if (ret)
    goto out;
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

No reason to allocate tp_module structures for modules that have no
tracepoints. This just wastes memory.

Fixes: b75ef8b4 "Tracepoint: Dissociate from module mutex"
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

If a failure occurs while modifying ftrace function, it bails out and will
remove the tracepoints to be back to what the code originally was.

There is missing the final sync run across the CPUs after the fix up is done
and before the ftrace int3 handler flag is reset.

Here's the description of the problem:

	CPU0				CPU1
	----				----
  remove_breakpoint();
  modifying_ftrace_code = 0;

				[still sees breakpoint]
				<takes trap>
				[sees modifying_ftrace_code as zero]
				[no breakpoint handler]
				[goto failed case]
				[trap exception - kernel breakpoint, no
				 handler]
				BUG()

Link: http://lkml.kernel.org/r/1393258342-29978-2-git-send-email-pmladek@suse.cz

Fixes: 8a4d0a68 "ftrace: Use breakpoint method to update ftrace caller"
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

If a failure occurs while enabling a trace, it bails out and will remove
the tracepoints to be back to what the code originally was. But the fix
up had some bugs in it. By injecting a failure in the code, the fix up
ran to completion, but shortly afterward the system rebooted.

There was two bugs here.

The first was that there was no final sync run across the CPUs after the
fix up was done, and before the ftrace int3 handler flag was reset. That
means that other CPUs could still see the breakpoint and trigger on it
long after the flag was cleared, and the int3 handler would think it was
a spurious interrupt. Worse yet, the int3 handler could hit other breakpoints
because the ftrace int3 handler flag would have prevented the int3 handler
from going further.

Here's a description of the issue:

	CPU0				CPU1
	----				----
  remove_breakpoint();
  modifying_ftrace_code = 0;

				[still sees breakpoint]
				<takes trap>
				[sees modifying_ftrace_code as zero]
				[no breakpoint handler]
				[goto failed case]
				[trap exception - kernel breakpoint, no
				 handler]
				BUG()

The second bug was that the removal of the breakpoints required the
"within()" logic updates instead of accessing the ip address directly.
As the kernel text is mapped read-only when CONFIG_DEBUG_RODATA is set, and
the removal of the breakpoint is a modification of the kernel text.
The ftrace_write() includes the "within()" logic, where as, the
probe_kernel_write() does not. This prevented the breakpoint from being
removed at all.

Link: http://lkml.kernel.org/r/1392650573-3390-1-git-send-email-pmladek@suse.czReported-by: Petr Mladek <pmladek@suse.cz>
Tested-by: Petr Mladek <pmladek@suse.cz>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

The ENABLED flag needs to be cleared when a ftrace_ops is unregistered
otherwise it wont be able to be registered again.

This is only for static tracing and does not affect DYNAMIC_FTRACE at
all.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Being able to change the trace clock at boot can be advantageous if
you need a better source of when things happen across CPUs. The default
trace clock is the fastest, but it uses local clocks which may not be
synced across CPUs and it does not let you know when events took place
with respect to events on other CPUs.

The global trace clock can help in this case, and if you do not care
about timings, the counter "clock" is the best, as that is just a  simple
atomic counter that is incremented for every event.

Usage is to add "trace_clock=counter" on the kernel command line. You
can replace counter with "global" or any of the clocks listed in
/sys/kernel/debug/tracing/trace_clock
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Appreciated-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

It seems there's no reason to prevent mixed used of ftrace and perf
for a single uprobe event.  At least the kprobes already support it.

Link: http://lkml.kernel.org/r/1389946120-19610-6-git-send-email-namhyung@kernel.orgReviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Add support for event triggering to uprobes.  This is same as kprobes
support added by Tom (plus cleanup by Steven).

Link: http://lkml.kernel.org/r/1389946120-19610-5-git-send-email-namhyung@kernel.orgReviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Support multi-buffer on uprobe-based dynamic events by
using ftrace_event_file.

This patch is based kprobe-based dynamic events multibuffer
support work initially, commited by Masami(commit 41a7dd42),
but revised as below:

Oleg changed the kprobe-based multibuffer design from
array-pointers of ftrace_event_file into simple list,
so this patch also change to the list design.

rcu_read_lock/unlock added into uprobe_trace_func/uretprobe_trace_func,
to synchronize with ftrace_event_file list add and delete.

Even though we allow multi-uprobes instances now,
but TP_FLAG_PROFILE/TP_FLAG_TRACE are still mutually exclusive
in probe_event_enable currently, this means we cannot allow
one user is using uprobe-tracer, and another user is using
perf-probe on same uprobe concurrently.
(Perhaps this will be fix in future, kprobe don't have this
limitation now)

Link: http://lkml.kernel.org/r/1389946120-19610-4-git-send-email-namhyung@kernel.orgReviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

A single uprobe event might serve different users like ftrace and
perf.  And this is especially important for upcoming multi buffer
support.  But in this case it'll fetch (same) data from userspace
multiple times.  So move it to the beginning of the dispatcher
function and reuse it for each users.

Link: http://lkml.kernel.org/r/1389946120-19610-3-git-send-email-namhyung@kernel.orgReviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

The uprobe_{trace,perf}_print functions are misnomers since what they
do is not printing.  There's also a real print function named
print_uprobe_event() so they'll only increase confusion IMHO.

Rename them with double underscores to follow convention of kprobe.

Link: http://lkml.kernel.org/r/1389946120-19610-2-git-send-email-namhyung@kernel.orgReviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Create a "set_ftrace_filter" and "set_ftrace_notrace" files in the instance
directories to let users filter of functions to trace for the given instance.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

In preparation for having the function tracing instances be able to
filter on functions, the generic filter functions must first be
converted to take in the global_ops as a parameter.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Allow instances (sub-buffers) to enable function tracing.
Each instance will have its own function tracing capability.
For now, instances will not have function stack tracing, or will
they be able to pick and choose what functions they can trace.

Picking and choosing their own functions will come later.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

As tracers will soon be used by instances, the tracer enabled field
needs to be converted to a counter instead of a boolean.
This counter is protected by the trace_types_lock mutex.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

When an instance is about to be deleted, make sure the tracer
is set to nop. If it isn't reset the tracer and set it to the nop
tracer, otherwise memory leaks and bad pointers may result.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

If global_ops function is being called directly, instead of the global_ops
list function, set the global_ops private to be the same as the ops private
that's being called directly.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Passing data to the function callback was originally done by adding the
ftrace_ops in another structure, and using the container_of() to get
the field. But this adds a bit more complexity than it is worth, and
adding a simple .private field to ftrace_ops makes things a lot easier.

But be warned, the .private data should not be freed once it is used
unless the ftrace_ops itself has gone through the necessary freeing
routines. A simple synchronize_sched() is not enough as functions
can be traced that are called outside the view of RCU and all its
concoctions.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Currently, only the top level instance can have tracing options.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Currently the tracers (function, function_graph, irqsoff, etc) can only
be used by the top level tracing directory (not for instances).

This sets up the infrastructure to allow instances to be able to
run a separate tracer apart from the what the top level tracing is
doing.

As tracers need to adapt for being used by instances, the tracers
must flag if they can be used by instances or not. Currently only the
'nop' tracer can be used by all instances.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

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

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: Steven Rostedt <rostedt@goodmis.org>

Pull btrfs fixes from Chris Mason:
 "We have a small collection of fixes in my for-linus branch.

  The big thing that stands out is a revert of a new ioctl.  Users
  haven't shipped yet in btrfs-progs, and Dave Sterba found a better way
  to export the information"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs:
  Btrfs: use right clone root offset for compressed extents
  btrfs: fix null pointer deference at btrfs_sysfs_add_one+0x105
  Btrfs: unset DCACHE_DISCONNECTED when mounting default subvol
  Btrfs: fix max_inline mount option
  Btrfs: fix a lockdep warning when cleaning up aborted transaction
  Revert "btrfs: add ioctl to export size of global metadata reservation"

Pull devicetree fixes from Rob Herring:
 "Fix booting on PPC boards.  Changes to of_match_node matching caused
  the serial port on some PPC boards to stop working.  Reverted the
  change and reimplement to split matching between new style compatible
  only matching and fallback to old matching algorithm"

* tag 'dt-fixes-for-3.14' of git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux:
  of: search the best compatible match first in __of_match_node()
  Revert "OF: base: match each node compatible against all given matches first"

Currently, of_match_node compares each given match against all node's
compatible strings with of_device_is_compatible.

To achieve multiple compatible strings per node with ordering from
specific to generic, this requires given matches to be ordered from
specific to generic. For most of the drivers this is not true and also
an alphabetical ordering is more sane there.

Therefore, this patch introduces a function to match each of the node's
compatible strings against all given compatible matches without type and
name first, before checking the next compatible string. This implies
that node's compatibles are ordered from specific to generic while
given matches can be in any order. If we fail to find such a match
entry, then fall-back to the old method in order to keep compatibility.

Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Tested-by: Stephen Chivers <schivers@csc.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Pull SCSI target fixes from Nicholas Bellinger:
 "Mostly minor fixes this time to v3.14-rc1 related changes.  Also
  included is one fix for a free after use regression in persistent
  reservations UNREGISTER logic that is CC'ed to >= v3.11.y stable"

* git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending:
  Target/sbc: Fix protection copy routine
  IB/srpt: replace strict_strtoul() with kstrtoul()
  target: Simplify command completion by removing CMD_T_FAILED flag
  iser-target: Fix leak on failure in isert_conn_create_fastreg_pool
  iscsi-target: Fix SNACK Type 1 + BegRun=0 handling
  target: Fix missing length check in spc_emulate_evpd_83()
  qla2xxx: Remove last vestiges of qla_tgt_cmd.cmd_list
  target: Fix 32-bit + CONFIG_LBDAF=n link error w/ sector_div
  target: Fix free-after-use regression in PR unregister

Pull i2c fixes from Wolfram Sang:
 "i2c has a bugfix and documentation improvements for you"

* 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux:
  Documentation: i2c: mention ACPI method for instantiating devices
  Documentation: i2c: describe devicetree method for instantiating devices
  i2c: mv64xxx: refactor message start to ensure proper initialization

Merge branches 'irq-urgent-for-linus' and 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull irq update from Thomas Gleixner:
 "Fix from the urgent branch: a trivial oneliner adding the missing
  Kconfig dependency curing build failures which have been discovered by
  several build robots.

  The update in the irq-core branch provides a new function in the
  irq/devres code, which is a prerequisite for driver developers to get
  rid of boilerplate code all over the place.

  Not a bugfix, but it has zero impact on the current kernel due to the
  lack of users.  It's simpler to provide the infrastructure to
  interested parties via your tree than fulfilling the wishlist of
  driver maintainers on which particular commit or tag this should be
  based on"

* 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  genirq: Add missing irq_to_desc export for CONFIG_SPARSE_IRQ=n

* 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  genirq: Add devm_request_any_context_irq()

Pull timer fixes from Thomas Gleixner:
 "The following trilogy of patches brings you:

   - fix for a long standing math overflow issue with HZ < 60

   - an onliner fix for a corner case in the dreaded tick broadcast
     mechanism affecting a certain range of AMD machines which are
     infested with the infamous automagic C1E power control misfeature

   - a fix for one of the ARM platforms which allows the kernel to
     proceed and boot instead of stupidly panicing for no good reason.
     The patch is slightly larger than necessary, but it's less ugly
     than the alternative 5 liner"

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  tick: Clear broadcast pending bit when switching to oneshot
  clocksource: Kona: Print warning rather than panic
  time: Fix overflow when HZ is smaller than 60

Merge tag 'trace-fixes-v3.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull twi tracing fixes from Steven Rostedt:
 "Two urgent fixes in the tracing utility.

  The first is a fix for the way the ring buffer stores timestamps.
  After a restructure of the code was done, the ring buffer timestamp
  logic missed the fact that the first event on a sub buffer is to have
  a zero delta, as the full timestamp is stored on the sub buffer
  itself.  But because the delta was not cleared to zero, the timestamp
  for that event will be calculated as the real timestamp + the delta
  from the last timestamp.  This can skew the timestamps of the events
  and have them say they happened when they didn't really happen.
  That's bad.

  The second fix is for modifying the function graph caller site.  When
  the stop machine was removed from updating the function tracing code,
  it missed updating the function graph call site location.  It is still
  modified as if it is being done via stop machine.  But it's not.  This
  can lead to a GPF and kernel crash if the function graph call site
  happens to lie between cache lines and one CPU is executing it while
  another CPU is doing the update.  It would be a very hard condition to
  hit, but the result is severe enough to have it fixed ASAP"

* tag 'trace-fixes-v3.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ftrace/x86: Use breakpoints for converting function graph caller
  ring-buffer: Fix first commit on sub-buffer having non-zero delta

Pull x86 EFI fixes from Peter Anvin:
 "A few more EFI-related fixes"

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/efi: Check status field to validate BGRT header
  x86/efi: Fix 32-bit fallout

Pull ARM SoC fixes from Kevin Hilman:
 "A collection of ARM SoC fixes for v3.14-rc1.

  Mostly a collection of Kconfig, device tree data and compilation fixes
  along with fix to drivers/phy that fixes a boot regression on some
  Marvell mvebu platforms"

* tag 'fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc:
  dma: mv_xor: Silence a bunch of LPAE-related warnings
  ARM: ux500: disable msp2 device tree node
  ARM: zynq: Reserve not DMAable space in front of the kernel
  ARM: multi_v7_defconfig: Select CONFIG_SOC_DRA7XX
  ARM: imx6: Initialize low-power mode early again
  ARM: pxa: fix various compilation problems
  ARM: pxa: fix compilation problem on AM300EPD board
  ARM: at91: add Atmel's SAMA5D3 Xplained board
  spi/atmel: document clock properties
  mmc: atmel-mci: document clock properties
  ARM: at91: enable USB host on at91sam9n12ek board
  ARM: at91/dt: fix sama5d3 ohci hclk clock reference
  ARM: at91/dt: sam9263: fix compatibility string for the I2C
  ata: sata_mv: Fix probe failures with optional phys
  drivers: phy: Add support for optional phys
  drivers: phy: Make NULL a valid phy reference
  ARM: fix HAVE_ARM_TWD selection for OMAP and shmobile
  ARM: moxart: move DMA_OF selection to driver
  ARM: hisi: fix kconfig warning on HAVE_ARM_TWD

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Guenter Roeck <linux@roeck-us.net>

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

For non compressed extents, iterate_extent_inodes() gives us offsets
that take into account the data offset from the file extent items, while
for compressed extents it doesn't. Therefore we have to adjust them before
placing them in a send clone instruction. Not doing this adjustment leads to
the receiving end requesting for a wrong a file range to the clone ioctl,
which results in different file content from the one in the original send
root.

Issue reproducible with the following excerpt from the test I made for
xfstests:

  _scratch_mkfs
  _scratch_mount "-o compress-force=lzo"

  $XFS_IO_PROG -f -c "truncate 118811" $SCRATCH_MNT/foo
  $XFS_IO_PROG -c "pwrite -S 0x0d -b 39987 92267 39987" $SCRATCH_MNT/foo

  $BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT $SCRATCH_MNT/mysnap1

  $XFS_IO_PROG -c "pwrite -S 0x3e -b 80000 200000 80000" $SCRATCH_MNT/foo
  $BTRFS_UTIL_PROG filesystem sync $SCRATCH_MNT
  $XFS_IO_PROG -c "pwrite -S 0xdc -b 10000 250000 10000" $SCRATCH_MNT/foo
  $XFS_IO_PROG -c "pwrite -S 0xff -b 10000 300000 10000" $SCRATCH_MNT/foo

  # will be used for incremental send to be able to issue clone operations
  $BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT $SCRATCH_MNT/clones_snap

  $BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT $SCRATCH_MNT/mysnap2

  $FSSUM_PROG -A -f -w $tmp/1.fssum $SCRATCH_MNT/mysnap1
  $FSSUM_PROG -A -f -w $tmp/2.fssum -x $SCRATCH_MNT/mysnap2/mysnap1 \
      -x $SCRATCH_MNT/mysnap2/clones_snap $SCRATCH_MNT/mysnap2
  $FSSUM_PROG -A -f -w $tmp/clones.fssum $SCRATCH_MNT/clones_snap \
      -x $SCRATCH_MNT/clones_snap/mysnap1 -x $SCRATCH_MNT/clones_snap/mysnap2

  $BTRFS_UTIL_PROG send $SCRATCH_MNT/mysnap1 -f $tmp/1.snap
  $BTRFS_UTIL_PROG send $SCRATCH_MNT/clones_snap -f $tmp/clones.snap
  $BTRFS_UTIL_PROG send -p $SCRATCH_MNT/mysnap1 \
      -c $SCRATCH_MNT/clones_snap $SCRATCH_MNT/mysnap2 -f $tmp/2.snap

  _scratch_unmount
  _scratch_mkfs
  _scratch_mount

  $BTRFS_UTIL_PROG receive $SCRATCH_MNT -f $tmp/1.snap
  $FSSUM_PROG -r $tmp/1.fssum $SCRATCH_MNT/mysnap1 2>> $seqres.full

  $BTRFS_UTIL_PROG receive $SCRATCH_MNT -f $tmp/clones.snap
  $FSSUM_PROG -r $tmp/clones.fssum $SCRATCH_MNT/clones_snap 2>> $seqres.full

  $BTRFS_UTIL_PROG receive $SCRATCH_MNT -f $tmp/2.snap
  $FSSUM_PROG -r $tmp/2.fssum $SCRATCH_MNT/mysnap2 2>> $seqres.full
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Chris Mason <clm@fb.com>

bdev is null when disk has disappeared and mounted with
the degrade option

stack trace
---------
btrfs_sysfs_add_one+0x105/0x1c0 [btrfs]
open_ctree+0x15f3/0x1fe0 [btrfs]
btrfs_mount+0x5db/0x790 [btrfs]
? alloc_pages_current+0xa4/0x160
mount_fs+0x34/0x1b0
vfs_kern_mount+0x62/0xf0
do_mount+0x22e/0xa80
? __get_free_pages+0x9/0x40
? copy_mount_options+0x31/0x170
SyS_mount+0x7e/0xc0
system_call_fastpath+0x16/0x1b
---------

reproducer:
-------
mkfs.btrfs -draid1 -mraid1 /dev/sdc /dev/sdd
(detach a disk)
devmgt detach /dev/sdc [1]
mount -o degrade /dev/sdd /btrfs
-------

[1] github.com/anajain/devmgt.git
Signed-off-by: Anand Jain <Anand.Jain@oracle.com>
Tested-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>