The master interface is a virtual interface that is registered
to mac80211, changing that does not seem like a good idea at
the moment. However, since it has no sdata, we cannot accept
any configuration for it. This patch makes the cfg80211 hooks
reject any such attempt.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Julius Volz pointed out that the dump callbacks in nl80211 were
broken and fixed one of them. This patch fixes the other three
and also addresses the TODOs there.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Julius Volz <juliusv@google.com>
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This patch fixes mac80211 to not use the skb->cb over the queue step
from virtual interfaces to the master. The patch also, for now,
disables aggregation because that would still require requeuing,
will fix that in a separate patch. There are two other places (software
requeue and powersaving stations) where requeue can happen, but that is
not currently used by any drivers/not possible to use respectively.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Wireless statistics produced by the RTL8187B driver are not particularly
informative about the strength of the received signal. From the data sheet
provided by Realtek, I discovered that certain parts of the RX header
should have the information necessary to calculate signal quality and
strength. With testing, it became clear that most of these quantities were
very jittery - only the AGC correlated with the signals expected from nearby
AP's. As a result, the quality and strength are derived from the agc value.
The scaling has been determined so that the numbers are close to those
obtained by b43 under the same conditions. The results are qualitatively
correct.
Statistics derived for the RTL8187 have not been changed.
The RX header variables have been renamed to match the quantites described
in the Realtek data sheet.
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
"mac80211: fix TX sequence numbers" broke rtl8187. This
patch makes the same kind of fix that was done for rt2x00. Note that
this code will have to be reworked for proper sequence numbers on beacons.
In addition, the sequence number has been placed in the hardware state,
not the vif state.
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
In net/mac80211/tx.c, there are some #ifdef which checks
MAC80211_VERBOSE_PS_DEBUG
(which in fact is never set) instead of
CONFIG_MAC80211_VERBOSE_PS_DEBUG, as should be.
This patch replaces MAC80211_VERBOSE_PS_DEBUG with
CONFIG_MAC80211_VERBOSE_PS_DEBUG in these #ifdef commands in
net/mac80211/tx.c.
Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
drivers/net/wireless/mac80211_hwsim.c:503:20: warning: Using plain integer as NULL pointer
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
ia64:
drivers/net/wireless/iwlwifi/iwl-led.c: In function `iwl_get_blink_rate':
drivers/net/wireless/iwlwifi/iwl-led.c:271: warning: long long int format, s64 arg (arg 6)
drivers/net/wireless/iwlwifi/iwl-led.c:271: warning: long long int format, u64 arg (arg 7)
We do not know what type the architecture uses to impement u64 and s64,
hence we must cast the variables for printing.
Cc: Tomas Winkler <tomas.winkler@intel.com>
Cc: John W. Linville <linville@tuxdriver.com>
Cc: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Return the proper error code rather than a hard-coded ENOMEM from
ieee80211_wep_init. Also, print the error code on failure.
Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Use dev_kfree_skb_any(); instead of dev_kfree_skb();, since
ieee80211_beacon_get function might be called from atomic.
(It's in a fail path.)
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Michael Wu <flamingice@sourmilk.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
When the queues are being initialized the entry flags fields must be
reset to 0. When this does not happen some entries might still be
marked as "occupied" after an ifdown & ifup cycle which would trigger
errors when the entry is being accessed:
phy0 -> rt2x00queue_write_tx_frame: Error - Arrived at non-free entry in the non-full queue 0.
Please file bug report to http://rt2x00.serialmonkey.com.
This also fixes the mac80211 warning:
------------[ cut here ]------------
WARNING: at net/mac80211/tx.c:1238 ieee80211_master_start_xmit+0x30a/0x350 [mac80211]()
which was triggered by the queue error.
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
rt2x00 will only perform configuration changes from
mac80211 when the configuration option has changed.
This means it keeps track of the current active configuration
and will check these values when the config() callback function
is used.
However this causes breakage when the interface has been
brought down and up again, since all stored active values
aren't reset while the registers might have.
This is for example the case with rt61pci antenna registers which
will jump to invalid values when the interface has been started.
To make sure a full configuration takes place after the start()
callback function, a new flag is added which will be checked
during config() and skips the "what's changed" phase.
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
The mutex is released on a successful return, so it would seem that it
should be released on an error return as well.
The semantic patch finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)
// <smpl>
@@
expression l;
@@
mutex_lock(l);
... when != mutex_unlock(l)
when any
when strict
(
if (...) { ... when != mutex_unlock(l)
+ mutex_unlock(l);
return ...;
}
|
mutex_unlock(l);
)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Michael Buesch <mb@bu3sch.de>
Cc: stable <stable@kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
The mutex is released on a successful return, so it would seem that it
should be released on an error return as well.
The semantic patch finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)
// <smpl>
@@
expression l;
@@
mutex_lock(l);
... when != mutex_unlock(l)
when any
when strict
(
if (...) { ... when != mutex_unlock(l)
+ mutex_unlock(l);
return ...;
}
|
mutex_unlock(l);
)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
When sending the RTS/CTS frame fails, we should
free the skb buffer which was created.
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
When IEEE80211_TX_CTL_ASSIGN_SEQ is not set,
the driver should disable hardware sequence counting
to make sure the mac80211 provided counter is used.
This fixes QOS sequence counting, since that is one
of the cases where mac80211 provides a seperate
sequence counter.
By moving the sequence counting code to rt2x00queue
we make sure that _all_ frames get the sequence counter,
including RTS/CTS and Beacon frames.
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
When setting up a beacon template, the length of the beacon is
calculated with the assumption that the SKB already contains
the Tx descriptor. In the case of beacons it doesn't.
This patch undoes the damage by adding the Tx descriptor length
to the beacon length. This is safe, because the shortest possible
beacon is longer than the Tx header.
Signed-off-by: Iwo Mergler <Iwo@call-direct.com.au>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Switches rt73usb to use large vendor requests for firmware
and beacons. This also fixes the garbled beacon bug.
Signed-off-by: Iwo Mergler <Iwo@call-direct.com.au>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Adds an extra rt2x00 vendor request function to support register
transfers beyond the CSR_CACHE_SIZE / USB packet size limit. This
is useful for firmware uploads, beacon templates and keys, all
of which are to large to do with a single USB request.
Signed-off-by: Iwo Mergler <Iwo@call-direct.com.au>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Olivier reported a difference between the EIFS
values used in the legacy driver and the one in
the rt2x00 drivers.
In rt2x00 the value was
( SIFS + (8 * (IEEE80211_HEADER + ACK_SIZE)) )
which comes down to 314us while the legacy driver uses the value 364us
This was caused because EIFS is: SIFS + DIFS + AckTime
This patch will fix this by adding the DIFS by the above value,
and creating a SHORT_EIFS define which uses the SHORT_DIFS.
Reported-by: Olivier Cornu <o.cornu@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
MSI is a nice thing, but we cannot enable it without changing the
interrupt handler. If we do it, we break MSI capable hardware,
specifically AR5006 chipset.
Signed-off-by: Pavel Roskin <proski@gnu.org>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
ath5k_beacon_update takes sc->lock upon entry. However, it is only
called from within ath5k_config_interface, which already holds the lock.
Remove the unnecessary locking from ath5k_beacon_update.
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
CC [M] drivers/net/wireless/iwlwifi/iwl-scan.o
drivers/net/wireless/iwlwifi/iwl-scan.c: In function 'iwl_rx_scan_complete_notif':
drivers/net/wireless/iwlwifi/iwl-scan.c:274: warning: unused variable 'scan_notif'
Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Tomas Winkler <tomasw@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
CC [M] drivers/net/wireless/iwlwifi/iwl-rfkill.o
drivers/net/wireless/iwlwifi/iwl-led.c: In function 'iwl_led_brightness_set':
drivers/net/wireless/iwlwifi/iwl-led.c:198: error: 'led_type_str' undeclared (first use in this function)
drivers/net/wireless/iwlwifi/iwl-led.c:198: error: (Each undeclared identifier is reported only once
drivers/net/wireless/iwlwifi/iwl-led.c:198: error: for each function it appears in.)
The problem is that led_type_str is defined under CONFIG_IWLWIFI_DEBUG
while IWL_DEBUG is a static inline function in this case. Replace it
with macro.
Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Some persistent settings were using hex and others decimal. In some cases,
values were set in hex but reported in decimal. Confusing.
Signed-off-by: Brian Cavagnolo <brian@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
When building the wireless-next-2.6 tree with CONFIG_IWL3945 (for building
iwl-3945 driver) and where CONFIG_IWL3945_LEDS is not set,
we get this warning:
drivers/net/wireless/iwlwifi/iwl-3945.c: In function
'iwl3945_pass_packet_to_mac80211':
drivers/net/wireless/iwlwifi/iwl-3945.c:633: warning: unused variable 'hdr'
This patch adds #ifdef to iwl3945_pass_packet_to_mac80211() to avoid this
warning. (The variable 'hdr' is used only if CONFIG_IWL3945_LEDS is set)
Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
For some stupid reason, I sent and old version of the patch minor kernel
doc-fix patch, and it got merged before I noticed the problem. This is an
incremental fix on top.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
There are two mutexes in rfkill:
rfkill->mutex, which protects some of the fields of a rfkill struct, and is
also used for callback serialization.
rfkill_mutex, which protects the global state, the list of registered
rfkill structs and rfkill->claim.
Make sure to use the correct mutex, and to not miss locking rfkill->mutex
even when we already took rfkill_mutex.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Reorder fields in struct rfkill and add comments to make it clear
which fields are protected by rfkill->mutex.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
rfkill needs to unregister the led trigger AFTER a call to
rfkill_remove_switch(), otherwise it will not update the LED state,
possibly leaving it ON when it should be OFF.
To make led-trigger unregistering safer, guard against unregistering a
trigger twice, and also against issuing trigger events to a led trigger
that was unregistered. This makes the error unwind paths more resilient.
Refer to "rfkill: Register LED triggers before registering switch".
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Cc: Michael Buesch <mb@bu3sch.de>
Cc: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
While the rfkill class does work with just get_state(), it doesn't work
well on devices that are subject to external events that cause rfkill state
changes.
Document that rfkill_force_state() is required in those cases.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Helge Deller reports that HP laptops (NC4010 and NC6000) use active-
high signals to turn on the LEDs. Previous code used active-low for
all devices.
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
- free and re-request irq since it might have changed during suspend
- disable and enable msi
- don't set D0 state of the device, it's already done by the PCI layer
- do restore_state before enable_device, it's safer
- check ath5k_init return value
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Cc: Luis R. Rodriguez <mcgrof@gmail.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Don't sync
- coherent mapping (descriptors)
- before unmap, it's useless
- (wrongly anyway -- for_cpu) beacon skb, it's just mapped,
so by the device yet
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Cc: Luis R. Rodriguez <mcgrof@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Make sure that the irq is not in progress after stop. This means
two things:
- ensure the intr setting register is set by flushing posted values
- call synchronize_irq() after that
Also flush stop tx write, inform callers of the tx stop about still
pending transfers (unsuccessful stop) and finally don't wait another
3ms in ath5k_rx_stop, since ath5k_hw_stop_rx_dma ensures transfer to
be finished.
Make sure all writes will be ordered in respect to locks by mmiowb().
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Cc: Luis R. Rodriguez <mcgrof@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Don't forget to kill tasklets on stop to not panic if they
fire after freeing some structures.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Cc: Luis R. Rodriguez <mcgrof@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
When signal is noisy, hardware can use all RX buffers and since the last
entry in the list is self-linked, it overwrites the entry until we link
new buffers.
Ensure that we don't free this last one until we are 100% sure that it
is not used by the hardware anymore to not cause memory curruption as
can be seen below.
This is done by checking next buffer in the list. Even after that we
know that the hardware refetched the new link and proceeded further
(the next buffer is ready) we can finally free the overwritten buffer.
We discard it since the status in its descriptor is overwritten (OR-ed
by new status) too.
=============================================================================
BUG kmalloc-4096: Poison overwritten
-----------------------------------------------------------------------------
INFO: 0xffff810067419060-0xffff810067419667. First byte 0x8 instead of 0x6b
INFO: Allocated in dev_alloc_skb+0x18/0x30 age=1118 cpu=1 pid=0
INFO: Freed in skb_release_data+0x85/0xd0 age=1105 cpu=1 pid=3718
INFO: Slab 0xffffe200019d0600 objects=7 used=0 fp=0xffff810067419048 flags=0x40000000000020c3
INFO: Object 0xffff810067419048 @offset=4168 fp=0xffff81006741c120
Bytes b4 0xffff810067419038: 4f 0b 02 00 01 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a O.......ZZZZZZZZ
Object 0xffff810067419048: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
Object 0xffff810067419058: 6b 6b 6b 6b 6b 6b 6b 6b 08 42 30 00 00 0b 6b 80 kkkkkkkk.B0...k.
Object 0xffff810067419068: f0 5d 00 4f 62 08 a3 64 00 0c 42 16 52 e4 f0 5a 360].Ob.243d..B.R344360Z
Object 0xffff810067419078: 68 81 00 00 7b a5 b4 be 7d 3b 8f 53 cd d5 de 12 h...{245264276};.S315325336.
Object 0xffff810067419088: 96 10 0b 89 48 54 23 41 0f 4e 2d b9 37 c3 cb 29 ....HT#A.N-2717303313)
Object 0xffff810067419098: d1 e0 de 14 8a 57 2a cc 3b 44 0d 78 7a 19 12 15 321340336..W*314;D.xz...
Object 0xffff8100674190a8: a9 ec d4 35 a8 10 ec 8c 40 a7 06 0a 51 a7 48 bb 2513543245250.354.@247..Q247H273
Object 0xffff8100674190b8: 3e cf a1 c7 38 60 63 3f 51 15 c7 20 eb ba 65 30 >ϡ3078`c?Q.307.353272e0
Redzone 0xffff81006741a048: bb bb bb bb bb bb bb bb 273273273273273273273273
Padding 0xffff81006741a088: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
Pid: 3297, comm: ath5k_pci Not tainted 2.6.26-rc8-mm1_64 #427
Call Trace:
[<ffffffff802a7306>] print_trailer+0xf6/0x150
[<ffffffff802a7485>] check_bytes_and_report+0x125/0x180
[<ffffffff802a75dc>] check_object+0xac/0x260
[<ffffffff802a9308>] __slab_alloc+0x368/0x6d0
[<ffffffff80544f82>] ? wireless_send_event+0x142/0x310
[<ffffffff804b1bd4>] ? __alloc_skb+0x44/0x150
[<ffffffff80544f82>] ? wireless_send_event+0x142/0x310
[<ffffffff802aa853>] __kmalloc_track_caller+0xc3/0xf0
[<ffffffff804b1bfe>] __alloc_skb+0x6e/0x150
[... stack snipped]
FIX kmalloc-4096: Restoring 0xffff810067419060-0xffff810067419667=0x6b
FIX kmalloc-4096: Marking all objects used
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Cc: Luis R. Rodriguez <mcgrof@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
I forgot this in the previous patch that made it unused.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
* 'hotfixes' of git://git.linux-nfs.org/projects/trondmy/nfs-2.6:
NFS: Ensure we call nfs_sb_deactive() after releasing the directory inode
nfs_remount oops when rebooting + possible fix
Simplify the code of include/linux/task_io_accounting.h.
It is also more reasonable to have all the task i/o-related statistics in a
single struct (task_io_accounting).
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
In order to avoid the "Busy inodes after unmount" error message, we need to
ensure that nfs_async_unlink_release() releases the super block after the
call to nfs_free_unlinkdata().
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
commit 3e9704739d ("x86: boot secondary
cpus through initial_code") causes the kernel to crash when a CPU is
brought online after the read only sections have been write
protected. The write to initial_code in do_boot_cpu() fails.
Move inital_code to .cpuinit.data section.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: H. Peter Anvin <hpa@zytor.com>
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394-2.6:
firewire: state userland requirements in Kconfig help
firewire: avoid memleak after phy config transmit failure
firewire: fw-ohci: TSB43AB22/A dualbuffer workaround
firewire: queue the right number of data
firewire: warn on unfinished transactions during card removal
firewire: small fw_fill_request cleanup
firewire: fully initialize fw_transaction before marking it pending
firewire: fix race of bus reset with request transmission
* git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6: (59 commits)
[SCSI] replace __FUNCTION__ with __func__
[SCSI] extend the last_sector_bug flag to cover more sectors
[SCSI] qla2xxx: Update version number to 8.02.01-k6.
[SCSI] qla2xxx: Additional NPIV corrections.
[SCSI] qla2xxx: suppress uninitialized-var warning
[SCSI] qla2xxx: use memory_read_from_buffer()
[SCSI] qla2xxx: Issue proper ISP callbacks during stop-firmware.
[SCSI] ch: fix ch_remove oops
[SCSI] 3w-9xxx: add MSI support and misc fixes
[SCSI] scsi_lib: use blk_rq_tagged in scsi_request_fn
[SCSI] ibmvfc: Update driver version to 1.0.1
[SCSI] ibmvfc: Add ADISC support
[SCSI] ibmvfc: Miscellaneous fixes
[SCSI] ibmvfc: Fix hang on module removal
[SCSI] ibmvfc: Target refcounting fixes
[SCSI] ibmvfc: Reduce unnecessary log noise
[SCSI] sym53c8xx: free luntbl in sym_hcb_free
[SCSI] scsi_scan.c: Release mutex in error handling code
[SCSI] scsi_eh_prep_cmnd should save scmd->underflow
[SCSI] sd: Support for SCSI disk (SBC) Data Integrity Field
...
