linux-toradex.git/drivers/block, branch v2.6.32.35 Linux kernel for Apalis and Colibri modules Fix pktcdvd ioctl dev_minor range check 2011-03-02T14:46:34+00:00 Dan Rosenberg drosenberg@vsecurity.com 2010-09-27T16:30:28+00:00 12d83a21da7510bbead571a15f24b4fbff47d3e2 commit 252a52aa4fa22a668f019e55b3aac3ff71ec1c29 upstream. The PKT_CTRL_CMD_STATUS device ioctl retrieves a pointer to a pktcdvd_device from the global pkt_devs array. The index into this array is provided directly by the user and is a signed integer, so the comparison to ensure that it falls within the bounds of this array will fail when provided with a negative index. This can be used to read arbitrary kernel memory or cause a crash due to an invalid pointer dereference. This can be exploited by users with permission to open /dev/pktcdvd/control (on many distributions, this is readable by group "cdrom"). Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com> [ Rather than add a cast, just make the function take the right type -Linus ] Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> 
commit 252a52aa4fa22a668f019e55b3aac3ff71ec1c29 upstream.

The PKT_CTRL_CMD_STATUS device ioctl retrieves a pointer to a
pktcdvd_device from the global pkt_devs array.  The index into this
array is provided directly by the user and is a signed integer, so the
comparison to ensure that it falls within the bounds of this array will
fail when provided with a negative index.

This can be used to read arbitrary kernel memory or cause a crash due to
an invalid pointer dereference.  This can be exploited by users with
permission to open /dev/pktcdvd/control (on many distributions, this is
readable by group "cdrom").

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
[ Rather than add a cast, just make the function take the right type -Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
loop: Update mtime when writing using aops 2010-08-13T20:20:23+00:00 Nikanth Karthikesan knikanth@suse.de 2010-04-08T19:39:31+00:00 bde7aceab9887be15a5df51d3369ccc95cc2f241 commit 02246c41171097ceab3246f6dc251ac89de6004b upstream. Update mtime when writing to backing filesystem using the address space operations write_begin and write_end. Signed-off-by: Nikanth Karthikesan <knikanth@suse.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> 
commit 02246c41171097ceab3246f6dc251ac89de6004b upstream.

Update mtime when writing to backing filesystem using the address space
operations write_begin and write_end.

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
cciss: Make cciss_seq_show handle holes in the h->drv[] array 2010-02-23T15:37:49+00:00 Stephen M. Cameron scameron@beardog.cce.hp.com 2010-02-05T12:14:04+00:00 2b8fcd4ed0db58421d1600ff6e3b01dd68b3ef83 commit 531c2dc70d339c5dfa8c3eb628c3459dc6f3a075 upstream. It is possible (and expected) for there to be holes in the h->drv[] array, that is, some elements may be NULL pointers. cciss_seq_show needs to be made aware of this possibility to avoid an Oops. To reproduce the Oops which this fixes: 1) Create two "arrays" in the Array Configuratino Utility and several logical drives on each array. 2) cat /proc/driver/cciss/cciss* in an infinite loop 3) delete some of the logical drives in the first "array." Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> 
commit 531c2dc70d339c5dfa8c3eb628c3459dc6f3a075 upstream.

It is possible (and expected) for there to be holes in the h->drv[]
array, that is, some elements may be NULL pointers.  cciss_seq_show
needs to be made aware of this possibility to avoid an Oops.

To reproduce the Oops which this fixes:

1) Create two "arrays" in the Array Configuratino Utility and
   several logical drives on each array.
2) cat /proc/driver/cciss/cciss* in an infinite loop
3) delete some of the logical drives in the first "array."

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
pktcdvd: removing device does not remove its sysfs dir 2010-02-09T12:51:01+00:00 Thadeu Lima de Souza Cascardo cascardo@holoscopio.com 2010-02-02T21:44:17+00:00 2c7f87e9dc8167999d4169b58f4be04fd357e9eb commit ca0bf64d99f6e3f6e2fe2585e52a0ac57354beac upstream. This is the counterpart to cba767175becadc5c4016cceb7bfdd2c7fe722f4 ("pktcdvd: remove broken dev_t export of class devices"). Device is not registered using dev_t, so it should not be destroyed using device_destroy which looks up the device by dev_t. This will fail and adding the device again will fail with the "duplicate name" error. This is fixed using device_unregister instead of device_destroy. Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com> Cc: Kay Sievers <kay.sievers@vrfy.org> Cc: Peter Osterlund <petero2@telia.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> 
commit ca0bf64d99f6e3f6e2fe2585e52a0ac57354beac upstream.

This is the counterpart to cba767175becadc5c4016cceb7bfdd2c7fe722f4
("pktcdvd: remove broken dev_t export of class devices").  Device is not
registered using dev_t, so it should not be destroyed using device_destroy
which looks up the device by dev_t.  This will fail and adding the device
again will fail with the "duplicate name" error.  This is fixed using
device_unregister instead of device_destroy.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Peter Osterlund <petero2@telia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
aoe: prevent cache aliases 2009-12-02T00:32:20+00:00 Peter Horton phorton@bitbox.co.uk 2009-12-01T21:17:46+00:00 0a1f127a0594d62cb23c26732686d0e2b097b264 Prevent the AoE block driver from creating cache aliases of page cache pages on machines with virtually indexed caches. Building kernels on an AT91SAM9G20 board without this patch fails with segmentation faults after a couple of passes. Signed-off-by: Peter Horton <zero@colonel-panic.org> Cc: "Ed L. Cashin" <ecashin@coraid.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> 
Prevent the AoE block driver from creating cache aliases of page cache
pages on machines with virtually indexed caches.

Building kernels on an AT91SAM9G20 board without this patch fails with
segmentation faults after a couple of passes.

Signed-off-by: Peter Horton <zero@colonel-panic.org>
Cc: "Ed L. Cashin" <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
cciss: make device attrs static 2009-11-13T07:47:53+00:00 Alex Chiang achiang@hp.com 2009-11-13T07:47:53+00:00 69ac74822277fa999a3f469d8362e93262deb3f4 No need to export those device attributes. In fact, without this patch, we can trip over a build error if cciss is a built-in and another driver also declares and exports attributes with the same name. You'll see errors like: drivers/scsi/built-in.o: multiple definition of `dev_attr_lunid' drivers/block/built-in.o: first defined here Cc: Stephen M. Cameron <scameron@beardog.cce.hp.com> Signed-off-by: Alex Chiang <achiang@hp.com> Cc: <mike.miller@hp.com> Cc: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com> 
No need to export those device attributes.

In fact, without this patch, we can trip over a build error if cciss
is a built-in and another driver also declares and exports attributes
with the same name.

You'll see errors like:

	drivers/scsi/built-in.o: multiple definition of `dev_attr_lunid'
	drivers/block/built-in.o: first defined here

Cc: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
Cc: <mike.miller@hp.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
loop: fix NULL dereference if mount fails 2009-10-29T14:39:27+00:00 Alexey Dobriyan adobriyan@gmail.com 2009-10-26T23:49:55+00:00 cf6e693212263d33c5882e4653df89a2fca4c0c4 Commit bb21488482bd36eae6b30b014d93619063773fd4 ("[PATCH] switch loop") started to pass NULL bdev to ioctl hook. Steps to reproduce: [boot with loop.max_part=1] [mount -o loop something so mount fails] BUG: unable to handle kernel NULL pointer dereference at 00000000000000b8 IP: [<ffffffff811486ee>] blkdev_ioctl+0x2e/0xa30 PGD 0 Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC last sysfs file: /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:35/ACPI0003:00/power_supply/ACAD/online CPU 0 Modules linked in: zfs nvidia(P) [last unloaded: zfs] Pid: 15177, comm: mount Tainted: P 2.6.32-rc4-zfs #2 Satellite X200 RIP: 0010:[<ffffffff811486ee>] [<ffffffff811486ee>] blkdev_ioctl+0x2e/0xa30 RSP: 0018:ffff88003b3d5bb8 EFLAGS: 00010286 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 000000000000125f RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffff88003b3d5ce8 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 00007ffffffff000 R13: 0000000000000000 R14: ffff880071cef280 R15: 00000000000200da FS: 00007fd77cfe7740(0000) GS:ffff880001600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 00000000000000b8 CR3: 0000000001001000 CR4: 00000000000026f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process mount (pid: 15177, threadinfo ffff88003b3d4000, task ffff88007572f920) Stack: ffff88003b3d5c38 ffffffff812f95f5 ffff88007eeb6600 0000000000000000 <0> 0000000000000000 ffff88003b3d5c18 ffffffff811547d9 ffff88001bf11ef0 <0> 7fffffffffffffff ffff88001bf11ee8 ffff88001bf11ef0 0000000000000000 Call Trace: [<ffffffff812f95f5>] ? schedule_timeout+0x1f5/0x250 [<ffffffff811547d9>] ? rb_insert_color+0x109/0x140 [<ffffffff812fb754>] ? _spin_unlock_irq+0x14/0x40 [<ffffffff812f84c6>] ? wait_for_common+0x66/0x170 [<ffffffff8105a280>] ? default_wake_function+0x0/0x10 [<ffffffff810f8258>] ioctl_by_bdev+0x38/0x50 [<ffffffff811d2481>] loop_clr_fd+0x1e1/0x210 [<ffffffff811d2522>] lo_release+0x72/0x80 [<ffffffff810f934c>] __blkdev_put+0x1ac/0x1d0 [<ffffffff810f937b>] blkdev_put+0xb/0x10 [<ffffffff810f93b9>] blkdev_close+0x39/0x60 [<ffffffff810ccef3>] __fput+0xd3/0x230 [<ffffffff810cd06d>] fput+0x1d/0x30 [<ffffffff810c9680>] filp_close+0x50/0x80 [<ffffffff81061f11>] put_files_struct+0x81/0x100 [<ffffffff81061fde>] exit_files+0x4e/0x60 [<ffffffff81063ec5>] do_exit+0x6b5/0x730 [<ffffffff8107b279>] ? up_read+0x9/0x10 [<ffffffff8104c86e>] ? do_page_fault+0x18e/0x2a0 [<ffffffff81063f81>] do_group_exit+0x41/0xc0 [<ffffffff81064012>] sys_exit_group+0x12/0x20 [<ffffffff81030deb>] system_call_fastpath+0x16/0x1b Code: f8 48 89 e5 48 81 ec 30 01 00 00 48 89 5d d8 4c 89 6d e8 4c 89 65 e0 4c 89 75 f0 4c 89 7d f8 48 89 bd e8 fe ff ff 49 89 cd 89 f3 <49> 8b 88 b8 00 00 00 81 fa 68 12 00 00 0f 84 57 05 00 00 0f 86 RIP [<ffffffff811486ee>] blkdev_ioctl+0x2e/0xa30 RSP <ffff88003b3d5bb8> CR2: 00000000000000b8 ---[ end trace c0b4d3c3118d1427 ]--- Fixing recursive fault but reboot is needed! Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Jens Axboe <jens.axboe@oracle.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> 
Commit bb21488482bd36eae6b30b014d93619063773fd4 ("[PATCH] switch loop")
started to pass NULL bdev to ioctl hook.

Steps to reproduce:

	[boot with loop.max_part=1]
	[mount -o loop something so mount fails]

BUG: unable to handle kernel NULL pointer dereference at 00000000000000b8
IP: [<ffffffff811486ee>] blkdev_ioctl+0x2e/0xa30
PGD 0
Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
last sysfs file: /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:35/ACPI0003:00/power_supply/ACAD/online
CPU 0
Modules linked in: zfs nvidia(P) [last unloaded: zfs]
Pid: 15177, comm: mount Tainted: P           2.6.32-rc4-zfs #2 Satellite X200
RIP: 0010:[<ffffffff811486ee>]  [<ffffffff811486ee>] blkdev_ioctl+0x2e/0xa30
RSP: 0018:ffff88003b3d5bb8  EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 000000000000125f RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88003b3d5ce8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00007ffffffff000
R13: 0000000000000000 R14: ffff880071cef280 R15: 00000000000200da
FS:  00007fd77cfe7740(0000) GS:ffff880001600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00000000000000b8 CR3: 0000000001001000 CR4: 00000000000026f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process mount (pid: 15177, threadinfo ffff88003b3d4000, task ffff88007572f920)
Stack:
 ffff88003b3d5c38 ffffffff812f95f5 ffff88007eeb6600 0000000000000000
<0> 0000000000000000 ffff88003b3d5c18 ffffffff811547d9 ffff88001bf11ef0
<0> 7fffffffffffffff ffff88001bf11ee8 ffff88001bf11ef0 0000000000000000
Call Trace:
 [<ffffffff812f95f5>] ? schedule_timeout+0x1f5/0x250
 [<ffffffff811547d9>] ? rb_insert_color+0x109/0x140
 [<ffffffff812fb754>] ? _spin_unlock_irq+0x14/0x40
 [<ffffffff812f84c6>] ? wait_for_common+0x66/0x170
 [<ffffffff8105a280>] ? default_wake_function+0x0/0x10
 [<ffffffff810f8258>] ioctl_by_bdev+0x38/0x50
 [<ffffffff811d2481>] loop_clr_fd+0x1e1/0x210
 [<ffffffff811d2522>] lo_release+0x72/0x80
 [<ffffffff810f934c>] __blkdev_put+0x1ac/0x1d0
 [<ffffffff810f937b>] blkdev_put+0xb/0x10
 [<ffffffff810f93b9>] blkdev_close+0x39/0x60
 [<ffffffff810ccef3>] __fput+0xd3/0x230
 [<ffffffff810cd06d>] fput+0x1d/0x30
 [<ffffffff810c9680>] filp_close+0x50/0x80
 [<ffffffff81061f11>] put_files_struct+0x81/0x100
 [<ffffffff81061fde>] exit_files+0x4e/0x60
 [<ffffffff81063ec5>] do_exit+0x6b5/0x730
 [<ffffffff8107b279>] ? up_read+0x9/0x10
 [<ffffffff8104c86e>] ? do_page_fault+0x18e/0x2a0
 [<ffffffff81063f81>] do_group_exit+0x41/0xc0
 [<ffffffff81064012>] sys_exit_group+0x12/0x20
 [<ffffffff81030deb>] system_call_fastpath+0x16/0x1b
Code: f8 48 89 e5 48 81 ec 30 01 00 00 48 89 5d d8 4c 89 6d e8 4c 89 65 e0 4c 89 75 f0 4c 89 7d f8 48 89 bd e8 fe ff ff 49 89 cd 89 f3 <49> 8b 88 b8 00 00 00 81 fa 68 12 00 00 0f 84 57 05 00 00 0f 86
RIP  [<ffffffff811486ee>] blkdev_ioctl+0x2e/0xa30
 RSP <ffff88003b3d5bb8>
CR2: 00000000000000b8
---[ end trace c0b4d3c3118d1427 ]---
Fixing recursive fault but reboot is needed!

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
virtio_blk: Revert serial number support 2009-10-22T06:09:30+00:00 Rusty Russell rusty@rustcorp.com.au 2009-10-22T22:39:28+00:00 3225beaba05d4f06087593f5e903ce867b6e118a This reverts "Add serial number support for virtio_blk, V4a". Turns out that virtio_pci, lguest and s/390 all have an 8 bit limit on virtio config space, so noone could ever use this. This is coming back later in a cleaner form. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: john cooper <john.cooper@redhat.com> Cc: Jens Axboe <jens.axboe@oracle.com> 
This reverts "Add serial number support for virtio_blk, V4a".

Turns out that virtio_pci, lguest and s/390 all have an 8 bit limit
on virtio config space, so noone could ever use this.

This is coming back later in a cleaner form.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: john cooper <john.cooper@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
virtio: let header files include virtio_ids.h 2009-10-22T06:09:28+00:00 Christian Borntraeger borntraeger@de.ibm.com 2009-09-30T09:17:21+00:00 e95646c3ec33c8ec0693992da4332a6b32eb7e31 Rusty, commit 3ca4f5ca73057a617f9444a91022d7127041970a virtio: add virtio IDs file moved all device IDs into a single file. While the change itself is a very good one, it can break userspace applications. For example if a userspace tool wanted to get the ID of virtio_net it used to include virtio_net.h. This does no longer work, since virtio_net.h does not include virtio_ids.h. This patch moves all "#include <linux/virtio_ids.h>" from the C files into the header files, making the header files compatible with the old ones. In addition, this patch exports virtio_ids.h to userspace. CC: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> 
Rusty,

commit 3ca4f5ca73057a617f9444a91022d7127041970a
    virtio: add virtio IDs file
moved all device IDs into a single file. While the change itself is
a very good one, it can break userspace applications. For example
if a userspace tool wanted to get the ID of virtio_net it used to
include virtio_net.h. This does no longer work, since virtio_net.h
does not include virtio_ids.h.
This patch moves all "#include <linux/virtio_ids.h>" from the C
files into the header files, making the header files compatible with
the old ones.

In addition, this patch exports virtio_ids.h to userspace.

CC: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
virtio_blk: revert QUEUE_FLAG_VIRT addition 2009-10-22T06:09:26+00:00 Christoph Hellwig hch@lst.de 2009-09-04T20:44:42+00:00 f8b12e513b953aebf30f8ff7d2de9be7e024dbbe It seems like the addition of QUEUE_FLAG_VIRT caueses major performance regressions for Fedora users: https://bugzilla.redhat.com/show_bug.cgi?id=509383 https://bugzilla.redhat.com/show_bug.cgi?id=505695 while I can't reproduce those extreme regressions myself I think the flag is wrong. Rationale: QUEUE_FLAG_VIRT expands to QUEUE_FLAG_NONROT which casus the queue unplugged immediately. This is not a good behaviour for at least qemu and kvm where we do have significant overhead for every I/O operations. Even with all the latested speeups (native AIO, MSI support, zero copy) we can only get native speed for up to 128kb I/O requests we already are down to 66% of native performance for 4kb requests even on my laptop running the Intel X25-M SSD for which the QUEUE_FLAG_NONROT was designed. If we ever get virtio-blk overhead low enough that this flag makes sense it should only be set based on a feature flag set by the host. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> 
It seems like the addition of QUEUE_FLAG_VIRT caueses major performance
regressions for Fedora users:

	https://bugzilla.redhat.com/show_bug.cgi?id=509383
	https://bugzilla.redhat.com/show_bug.cgi?id=505695

while I can't reproduce those extreme regressions myself I think the flag
is wrong.

Rationale:

  QUEUE_FLAG_VIRT expands to QUEUE_FLAG_NONROT which casus the queue
  unplugged immediately.  This is not a good behaviour for at least
  qemu and kvm where we do have significant overhead for every
  I/O operations.  Even with all the latested speeups (native AIO,
  MSI support, zero copy) we can only get native speed for up to 128kb
  I/O requests we already are down to 66% of native performance for 4kb
  requests even on my laptop running the Intel X25-M SSD for which the
  QUEUE_FLAG_NONROT was designed.
  If we ever get virtio-blk overhead low enough that this flag makes
  sense it should only be set based on a feature flag set by the host.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>