negotiate_mq should happen in all cases of a new VBD being discovered by
xen-blkfront, whether called through _probe() or a hot-attached new VBD
from dom-0 via xenstore. Otherwise, hot-attached new VBDs are left
configured without multi-queue.
Signed-off-by: NBhavesh Davda <bhavesh.davda@oracle.com>
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Signed-off-by: NBart Van Assche <bart.vanassche@wdc.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Roger Pau Monn303251 <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Since commit d05d7f40 ("Merge branch 'for-4.8/core' of
git://git.kernel.dk/linux-block") and 3fc9d690 ("Merge branch
'for-4.8/drivers' of git://git.kernel.dk/linux-block"), blkfront_resume()
has been using an index for iterating ring_info to check request when
iterating blk_shadow in an inner loop. This seems to have been
accidentally introduced during the massive rewrite of the block layer
macros in the commits.

This may cause crash like this:

[11798.057074] BUG: unable to handle kernel NULL pointer dereference at 0000000000000048
[11798.058832] IP: [<ffffffff814411fa>] blkfront_resume+0x10a/0x610
....
[11798.061063] Call Trace:
[11798.061063]  [<ffffffff8139ce93>] xenbus_dev_resume+0x53/0x140
[11798.061063]  [<ffffffff8139ce40>] ? xenbus_dev_probe+0x150/0x150
[11798.061063]  [<ffffffff813f359e>] dpm_run_callback+0x3e/0x110
[11798.061063]  [<ffffffff813f3a08>] device_resume+0x88/0x190
[11798.061063]  [<ffffffff813f4cc0>] dpm_resume+0x100/0x2d0
[11798.061063]  [<ffffffff813f5221>] dpm_resume_end+0x11/0x20
[11798.061063]  [<ffffffff813950a8>] do_suspend+0xe8/0x1a0
[11798.061063]  [<ffffffff813954bd>] shutdown_handler+0xfd/0x130
[11798.061063]  [<ffffffff8139aba0>] ? split+0x110/0x110
[11798.061063]  [<ffffffff8139ac26>] xenwatch_thread+0x86/0x120
[11798.061063]  [<ffffffff810b4570>] ? prepare_to_wait_event+0x110/0x110
[11798.061063]  [<ffffffff8108fe57>] kthread+0xd7/0xf0
[11798.061063]  [<ffffffff811da811>] ? kfree+0x121/0x170
[11798.061063]  [<ffffffff8108fd80>] ? kthread_park+0x60/0x60
[11798.061063]  [<ffffffff810863b0>] ?  call_usermodehelper_exec_work+0xb0/0xb0
[11798.061063]  [<ffffffff810864ea>] ?  call_usermodehelper_exec_async+0x13a/0x140
[11798.061063]  [<ffffffff81534a45>] ret_from_fork+0x25/0x30

Use the right index in the inner loop.

Fixes: d05d7f40 ("Merge branch 'for-4.8/core' of git://git.kernel.dk/linux-block")
Fixes: 3fc9d690 ("Merge branch 'for-4.8/drivers' of git://git.kernel.dk/linux-block")
Signed-off-by: NMunehisa Kamata <kamatam@amazon.com>
Reviewed-by: NThomas Friebel <friebelt@amazon.de>
Reviewed-by: NEduardo Valentin <eduval@amazon.com>
Reviewed-by: NBoris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: NRoger Pau Monne <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org
Cc: stable@vger.kernel.org
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

This patch partially reverts 3df0e505 ("xen/blkfront: pseudo support for
multi hardware queues/rings"). The xen-blkfront queue/ring might hang due
to grants allocation failure in the situation when gnttab_free_head is
almost empty while many persistent grants are reserved for this queue/ring.

As persistent grants management was per-queue since 73716df7 ("xen/blkfront:
make persistent grants pool per-queue"), we should always allocate from
persistent grants first.
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NDongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

When ring buf full, hw queue will be stopped. While blkif interrupt consume
request and make free space in ring buf, hw queue will be started again.
But since start queue is protected by spin lock while stop not, that will
cause a race.

interrupt:                                      process:
blkif_interrupt()                               blkif_queue_rq()
 kick_pending_request_queues_locked()
   blk_mq_start_stopped_hw_queues()
      clear_bit(BLK_MQ_S_STOPPED, &hctx->state)
	                                             blk_mq_stop_hw_queue(hctx)
	  blk_mq_run_hw_queue(hctx, async)

If ring buf is made empty in this case, interrupt will never come, then the
hw queue will be stopped forever, all processes waiting for the pending io
in the queue will hung.
Signed-off-by: NJunxiao Bi <junxiao.bi@oracle.com>
Reviewed-by: NAnkur Arora <ankur.a.arora@oracle.com>
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

This patch fixes the following sparse warnings:

drivers/block/xen-blkfront.c:916:45: warning: incorrect type in argument 2 (different base types)
drivers/block/xen-blkfront.c:916:45:    expected restricted blk_status_t [usertype] error
drivers/block/xen-blkfront.c:916:45:    got int [signed] error
drivers/block/xen-blkfront.c:1599:47: warning: incorrect type in assignment (different base types)
drivers/block/xen-blkfront.c:1599:47:    expected int [signed] error
drivers/block/xen-blkfront.c:1599:47:    got restricted blk_status_t [usertype] <noident>
drivers/block/xen-blkfront.c:1607:55: warning: incorrect type in assignment (different base types)
drivers/block/xen-blkfront.c:1607:55:    expected int [signed] error
drivers/block/xen-blkfront.c:1607:55:    got restricted blk_status_t [usertype] <noident>
drivers/block/xen-blkfront.c:1625:55: warning: incorrect type in assignment (different base types)
drivers/block/xen-blkfront.c:1625:55:    expected int [signed] error
drivers/block/xen-blkfront.c:1625:55:    got restricted blk_status_t [usertype] <noident>
drivers/block/xen-blkfront.c:1628:62: warning: restricted blk_status_t degrades to integer

Compile-tested only.

Fixes: commit 2a842aca ("block: introduce new block status code type")
Signed-off-by: NBart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Roger Pau Monné <roger.pau@citrix.com>
Cc: <xen-devel@lists.xenproject.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

For historical reasons we default to bouncing highmem pages for all block
queues.  But the blk-mq drivers are easy to audit to ensure that we don't
need this - scsi and mtip32xx set explicit limits and everyone else doesn't
have any particular ones.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

bios that are re-submitted will pass through blk_queue_split() when
blk_queue_bio() is called, and this will split the bio if necessary.
There is no longer any need to do this splitting in xen-blkfront.
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NNeilBrown <neilb@suse.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>

Use the same values for use for request completion errors as the return
value from ->queue_rq.  BLK_STS_RESOURCE is special cased to cause
a requeue, and all the others are completed as-is.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Currently we use nornal Linux errno values in the block layer, and while
we accept any error a few have overloaded magic meanings.  This patch
instead introduces a new  blk_status_t value that holds block layer specific
status codes and explicitly explains their meaning.  Helpers to convert from
and to the previous special meanings are provided for now, but I suspect
we want to get rid of them in the long run - those drivers that have a
errno input (e.g. networking) usually get errnos that don't know about
the special block layer overloads, and similarly returning them to userspace
will usually return somethings that strictly speaking isn't correct
for file system operations, but that's left as an exercise for later.

For now the set of errors is a very limited set that closely corresponds
to the previous overloaded errno values, but there is some low hanging
fruite to improve it.

blk_status_t (ab)uses the sparse __bitwise annotations to allow for sparse
typechecking, so that we can easily catch places passing the wrong values.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Now that all drivers that call blk_mq_complete_requests have a
->complete callback we can remove the direct call to blk_mq_end_request,
as well as the error argument to blk_mq_complete_request.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NBart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

xen-blkfron is the last users using rq->errros for passing back error to
blk-mq, and I'd like to get rid of that.  In the longer run the driver
should be moving more of the completion processing into .complete, but
this is the minimal change to move forward for now.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
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>

When a blkfront device is resized from dom0, emit a KOBJ_CHANGE uevent to
notify the guest about the change. This allows for custom udev rules, such
as automatically resizing a filesystem, when an event occurs.

With this patch you get these udev

KERNEL[577.206230] change   /devices/vbd-51728/block/xvdb (block)
UDEV  [577.226218] change   /devices/vbd-51728/block/xvdb (block)
Signed-off-by: NMarc Olson <marcolso@amazon.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Constify all instances of blk_mq_ops, as they are never modified.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Instead of keeping two levels of indirection for requests types, fold it
all into the operations.  The little caveat here is that previously
cmd_type only applied to struct request, while the request and bio op
fields were set to plain REQ_OP_READ/WRITE even for passthrough
operations.

Instead this patch adds new REQ_OP_* for SCSI passthrough and driver
private requests, althought it has to add two for each so that we
can communicate the data in/out nature of the request.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Making use of "max_indirect_segments=" has issues:
- blkfront_setup_indirect() may end up with zero psegs when PAGE_SIZE
  is sufficiently much larger than XEN_PAGE_SIZE
- the variable driven by the command line option
  (xen_blkif_max_segments) has a somewhat different purpose, and hence
  should namely never end up being zero
- as long as the specified value is lower than the legacy default,
  we better don't use indirect segments at all (or we'd in fact lower
  throughput)
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Don't truncate the "feature-persistent" value read from xenstore: Any
non-zero value is supposed to enable the feature, just like is already
being done for feature_secdiscard.

Just like the other feature_* fields, feature_flush and feature_fua are
boolean flags, and hence fit well into a single bit.

Keep all bit fields together to limit gaps.
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Use xenbus_read_unsigned() instead of xenbus_scanf() when possible.
This requires to change the type of some reads from int to unsigned,
but these cases have been wrong before: negative values are not allowed
for the modified cases.

Cc: konrad.wilk@oracle.com
Cc: roger.pau@citrix.com
Signed-off-by: NJuergen Gross <jgross@suse.com>
Acked-by: NDavid Vrabel <david.vrabel@citrix.com>

Most blk_mq_requeue_request() and blk_mq_add_to_requeue_list() calls
are followed by kicking the requeue list. Hence add an argument to
these two functions that allows to kick the requeue list. This was
proposed by Christoph Hellwig.
Signed-off-by: NBart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>
Signed-off-by: NJens Axboe <axboe@fb.com>

Since blk_mq_requeue_work() starts stopped queues and since
execution of this function can be scheduled after a queue has
been stopped it is not possible to stop queues without using
an additional state variable to track whether or not the queue
has been stopped. Hence modify blk_mq_requeue_work() such that it
does not start stopped queues. My conclusion after a review of
the blk_mq_stop_hw_queues() and blk_mq_{delay_,}kick_requeue_list()
callers is as follows:
* In the dm driver starting and stopping queues should only happen
  if __dm_suspend() or __dm_resume() is called and not if the
  requeue list is processed.
* In the SCSI core queue stopping and starting should only be
  performed by the scsi_internal_device_block() and
  scsi_internal_device_unblock() functions but not by any other
  function. Although the blk_mq_stop_hw_queue() call in
  scsi_queue_rq() may help to reduce CPU load if a LLD queue is
  full, figuring out whether or not a queue should be restarted
  when requeueing a command would require to introduce additional
  locking in scsi_mq_requeue_cmd() to avoid a race with
  scsi_internal_device_block(). Avoid this complexity by removing
  the blk_mq_stop_hw_queue() call from scsi_queue_rq().
* In the NVMe core only the functions that call
  blk_mq_start_stopped_hw_queues() explicitly should start stopped
  queues.
* A blk_mq_start_stopped_hwqueues() call must be added in the
  xen-blkfront driver in its blkif_recover() function.
Signed-off-by: NBart Van Assche <bart.vanassche@sandisk.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Roger Pau Monné <roger.pau@citrix.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: James Bottomley <jejb@linux.vnet.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

All drivers use the default, so provide an inline version of it.  If we
ever need other queue mapping we can add an optional method back,
although supporting will also require major changes to the queue setup
code.

This provides better code generation, and better debugability as well.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NKeith Busch <keith.busch@intel.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Current code forgets to free resources in the failure path of
xlvbd_alloc_gendisk(), this patch fix it.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

blk_mq_update_nr_hw_queues() reset all queue limits to default which it's
not as xen-blkfront expected, introducing blkif_set_queue_limits() to reset
limits with initial correct values.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Two places didn't get updated when 64KB page granularity was introduced,
this patch fix them.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

... for single items being collected: It is more typesafe (as the
compiler can check format string and to-be-written-to variable match)
and requires one less parameter to be passed.
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Acked-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Uncompleted reqs used to be 'saved and resubmitted' in blkfront_recover() during
migration, but that's too late after multi-queue was introduced.

After a migrate to another host (which may not have multiqueue support), the
number of rings (block hardware queues) may be changed and the ring and shadow
structure will also be reallocated.

The blkfront_recover() then can't 'save and resubmit' the real
uncompleted reqs because shadow structure have been reallocated.

This patch fixes this issue by moving the 'save' logic out of
blkfront_recover() to earlier place in blkfront_resume().

The 'resubmit' is not changed and still in blkfront_recover().
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: stable@vger.kernel.org

For block drivers that specify a parent device, convert them to use
device_add_disk().

This conversion was done with the following semantic patch:

    @@
    struct gendisk *disk;
    expression E;
    @@

    - disk->driverfs_dev = E;
    ...
    - add_disk(disk);
    + device_add_disk(E, disk);

    @@
    struct gendisk *disk;
    expression E1, E2;
    @@

    - disk->driverfs_dev = E1;
    ...
    E2 = disk;
    ...
    - add_disk(E2);
    + device_add_disk(E1, E2);

...plus some manual fixups for a few missed conversions.

Cc: Jens Axboe <axboe@fb.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.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>

After a migrate to another host (which may not have multiqueue
support), the number of rings (block hardware queues)
may be changed and the ring info structure will also be reallocated.

This patch fixes two related bugs:
 * call blk_mq_update_nr_hw_queues() to make blk-core know the number
   of hardware queues have been changed.
 * Don't store rinfo pointer to hctx->driver_data, because rinfo may be
   reallocated so use hctx->queue_num to get the rinfo structure instead.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Sometimes blkfront may twice receive blkback_changed() notification
(XenbusStateConnected) after migration, which will cause
talk_to_blkback() to be called twice too and confuse xen-blkback.

The flow is as follow:
   blkfront                                        blkback
blkfront_resume()
 > talk_to_blkback()
  > Set blkfront to XenbusStateInitialised
                                                front changed()
                                                 > Connect()
                                                  > Set blkback to XenbusStateConnected

blkback_changed()
 > Skip talk_to_blkback()
   because frontstate == XenbusStateInitialised
 > blkfront_connect()
  > Set blkfront to XenbusStateConnected

-----
And here we get another XenbusStateConnected notification leading
to:
-----
blkback_changed()
 > because now frontstate != XenbusStateInitialised
   talk_to_blkback() is also called again
  > blkfront state changed from
  XenbusStateConnected to XenbusStateInitialised
    (Which is not correct!)

						front_changed():
                                                 > Do nothing because blkback
                                                   already in XenbusStateConnected

Now blkback is in XenbusStateConnected but blkfront is still
in XenbusStateInitialised - leading to no disks.

Poking of the XenbusStateConnected state is allowed (to deal with
block disk change) and has to be dealt with. The most likely
cause of this bug are custom udev scripts hooking up the disks
and then validating the size.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

The last patch added a REQ_OP_FLUSH for request_fn drivers
and the next patch renames REQ_FLUSH to REQ_PREFLUSH which
will be used by file systems and make_request_fn drivers so
they can send a write/flush combo.

This patch drops xen's use of REQ_FLUSH to track if it supports
REQ_OP_FLUSH requests, so REQ_FLUSH can be deleted.
Signed-off-by: NMike Christie <mchristi@redhat.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NJuergen Gross <kernel@pfupf.net>
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>

The req operation REQ_OP is separated from the rq_flag_bits
definition. This converts the block layer drivers to
use req_op to get the op from the request struct.
Signed-off-by: NMike Christie <mchristi@redhat.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This has callers of submit_bio/submit_bio_wait set the bio->bi_rw
instead of passing it in. This makes that use the same as
generic_make_request and how we set the other bio fields.
Signed-off-by: NMike Christie <mchristi@redhat.com>

Fixed up fs/ext4/crypto.c
Signed-off-by: NJens Axboe <axboe@fb.com>

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

"max" is rather ambiguous and carries pretty little meaning, the more
that there are also "max_queues" and "max_ring_page_order". Make this
"max_indirect_segments" instead, and at once change the type from int
to uint (to match the respective variable's type).
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Need to reallocate ring info in the resume path, because info->rinfo was freed
in blkif_free(). And 'multi-queue-max-queues' backend reports may have been
changed.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Reported-and-Tested-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

We have split the setting up of all the resources in two steps:
1) talk_to_blkback  - which figures out the num_ring_pages (from
   the default value of zero), sets up shadow and so
2) blkfront_connect - does the real part of filling out the
   internal structures.

The problem is if we bypass the 1) step and go straight to 2)
and call blkfront_setup_indirect where we use the macro
BLK_RING_SIZE - which returns an negative value (because
sz is zero  - since num_ring_pages is zero - since it has never
been set).

We can fix this by making sure that we always have called
talk_to_blkback before going to blkfront_connect.

Or we could set in blkfront_probe info->nr_ring_pages = 1
to have a default value. But that looks odd - as we haven't
actually negotiated any ring size.

This patch changes XenbusStateConnected state to detect if
we haven't done the initial handshake - and if so continue
on as if were in XenbusStateInitWait state.

We also roll the error recovery (freeing the structure) into
talk_to_blkback error path - which is safe since that function
is only called from blkback_changed.
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

The minimal size of request in the block framework is always PAGE_SIZE.
It means that when 64KB guest is support, the request will at least be
64KB.

Although, if the backend doesn't support indirect descriptor (such as QDISK
in QEMU), a ring request is only able to accommodate 11 segments of 4KB
(i.e 44KB).

The current frontend is assuming that an I/O request will always fit in
a ring request. This is not true any more when using 64KB page
granularity and will therefore crash during boot.

On ARM64, the ABI is completely neutral to the page granularity used by
the domU. The guest has the choice between different page granularity
supported by the processors (for instance on ARM64: 4KB, 16KB, 64KB).
This can't be enforced by the hypervisor and therefore it's possible to
run guests using different page granularity.

So we can't mandate the block backend to support indirect descriptor
when the frontend is using 64KB page granularity and have to fix it
properly in the frontend.

The solution exposed below is based on modifying directly the frontend
guest rather than asking the block framework to support smaller size
(i.e < PAGE_SIZE). This is because the change is the block framework are
not trivial as everything seems to relying on a struct *page (see [1]).
Although, it may be possible that someone succeed to do it in the future
and we would therefore be able to use it.

Given that a block request may not fit in a single ring request, a
second request is introduced for the data that cannot fit in the first
one. This means that the second ring request should never be used on
Linux if the page size is smaller than 44KB.

To achieve the support of the extra ring request, the block queue size
is divided by two. Therefore, the ring will always contain enough space
to accommodate 2 ring requests. While this will reduce the overall
performance, it will make the implementation more contained. The way
forward to get better performance is to implement in the backend either
indirect descriptor or multiple grants ring.

Note that the parameters blk_queue_max_* helpers haven't been updated.
The block code will set the mimimum size supported and we may be able
to support directly any change in the block framework that lower down
the minimal size of a request.

[1] http://lists.xen.org/archives/html/xen-devel/2015-08/msg02200.htmlSigned-off-by: NJulien Grall <julien.grall@citrix.com>
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>