Hans Verkuil
626cf23660
poll: add poll_requested_events() and poll_does_not_wait() functions ...
In some cases the poll() implementation in a driver has to do different
things depending on the events the caller wants to poll for. An example
is when a driver needs to start a DMA engine if the caller polls for
POLLIN, but doesn't want to do that if POLLIN is not requested but instead
only POLLOUT or POLLPRI is requested. This is something that can happen
in the video4linux subsystem among others.
Unfortunately, the current epoll/poll/select implementation doesn't
provide that information reliably. The poll_table_struct does have it: it
has a key field with the event mask. But once a poll() call matches one
or more bits of that mask any following poll() calls are passed a NULL
poll_table pointer.
Also, the eventpoll implementation always left the key field at ~0 instead
of using the requested events mask.
This was changed in eventpoll.c so the key field now contains the actual
events that should be polled for as set by the caller.
The solution to the NULL poll_table pointer is to set the qproc field to
NULL in poll_table once poll() matches the events, not the poll_table
pointer itself. That way drivers can obtain the mask through a new
poll_requested_events inline.
The poll_table_struct can still be NULL since some kernel code calls it
internally (netfs_state_poll() in ./drivers/staging/pohmelfs/netfs.h). In
that case poll_requested_events() returns ~0 (i.e. all events).
Very rarely drivers might want to know whether poll_wait will actually
wait. If another earlier file descriptor in the set already matched the
events the caller wanted to wait for, then the kernel will return from the
select() call without waiting. This might be useful information in order
to avoid doing expensive work.
A new helper function poll_does_not_wait() is added that drivers can use
to detect this situation. This is now used in sock_poll_wait() in
include/net/sock.h. This was the only place in the kernel that needed
this information.
Drivers should no longer access any of the poll_table internals, but use
the poll_requested_events() and poll_does_not_wait() access functions
instead. In order to enforce that the poll_table fields are now prepended
with an underscore and a comment was added warning against using them
directly.
This required a change in unix_dgram_poll() in unix/af_unix.c which used
the key field to get the requested events. It's been replaced by a call
to poll_requested_events().
For qproc it was especially important to change its name since the
behavior of that field changes with this patch since this function pointer
can now be NULL when that wasn't possible in the past.
Any driver accessing the qproc or key fields directly will now fail to compile.
Some notes regarding the correctness of this patch: the driver's poll()
function is called with a 'struct poll_table_struct *wait' argument. This
pointer may or may not be NULL, drivers can never rely on it being one or
the other as that depends on whether or not an earlier file descriptor in
the select()'s fdset matched the requested events.
There are only three things a driver can do with the wait argument:
1) obtain the key field:
events = wait ? wait->key : ~0;
This will still work although it should be replaced with the new
poll_requested_events() function (which does exactly the same).
This will now even work better, since wait is no longer set to NULL
unnecessarily.
2) use the qproc callback. This could be deadly since qproc can now be
NULL. Renaming qproc should prevent this from happening. There are no
kernel drivers that actually access this callback directly, BTW.
3) test whether wait == NULL to determine whether poll would return without
waiting. This is no longer sufficient as the correct test is now
wait == NULL || wait->_qproc == NULL.
However, the worst that can happen here is a slight performance hit in
the case where wait != NULL and wait->_qproc == NULL. In that case the
driver will assume that poll_wait() will actually add the fd to the set
of waiting file descriptors. Of course, poll_wait() will not do that
since it tests for wait->_qproc. This will not break anything, though.
There is only one place in the whole kernel where this happens
(sock_poll_wait() in include/net/sock.h) and that code will be replaced
by a call to poll_does_not_wait() in the next patch.
Note that even if wait->_qproc != NULL drivers cannot rely on poll_wait()
actually waiting. The next file descriptor from the set might match the
event mask and thus any possible waits will never happen.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-03-23 16:58:38 -07:00
SPI changes for v3.4.
2012-03-21 10:32:00 -07:00
bcma: add support for on-chip OTP memory used for SPROM storage
2012-03-06 15:16:18 -05:00
Merge branch 'drm-next' of git://people.freedesktop.org/~airlied/linux
2012-03-22 13:08:22 -07:00
Input: ili210x - add support for Ilitek ILI210x based touchscreens
2012-03-17 12:20:44 -07:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
2012-03-22 20:20:18 -07:00
InfiniBand/RDMA changes for the 3.4 merge window. Nothing big really
2012-03-21 10:33:42 -07:00
headers: include linux/types.h where appropriate
2012-03-23 16:58:31 -07:00
netfilter: xt_CT: allow to attach timeout policy + glue code
2012-03-07 17:41:28 +01:00
netfilter: remove ipt_SAME.h and ipt_realm.h
2012-03-07 17:40:56 +01:00
netfilter: merge ipt_LOG and ip6_LOG into xt_LOG
2012-03-07 17:40:49 +01:00
pinctrl: introduce generic pin config
2012-03-12 22:49:02 +01:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
2012-03-22 20:20:18 -07:00
md: Use existed macros instead of numbers
2012-03-13 11:21:23 +11:00
Merge remote-tracking branch 'regulator/topic/supply' into regulator-next
2012-03-18 21:39:19 +00:00
spi: sh-hspi: control spi clock more correctly
2012-03-15 03:41:01 -06:00
ssb: add some missing sprom attributes
2012-03-05 15:20:49 -05:00
SUNRPC: Kill compiler warning when RPC_DEBUG is unset
2012-03-21 09:31:31 -04:00
USB: EHCI: Add a generic platform device driver
2012-03-15 12:42:07 -07:00
atomic: Allow atomic_inc_not_zero to be overridden
2012-03-07 17:06:08 +11:00
constify path argument of audit_log_d_path()
2012-03-20 21:29:40 -04:00
__register_binfmt() made void
2012-03-20 21:29:46 -04:00
fs: remove the second argument of k[un]map_atomic()
2012-03-20 21:48:21 +08:00
bitops: introduce for_each_clear_bit()
2012-03-23 16:58:34 -07:00
cgroup: revert ss_id_lock to spinlock
2012-03-21 17:55:01 -07:00
vmscan: only defer compaction for failed order and higher
2012-03-21 17:54:56 -07:00
include/ and checkpatch: prefer __scanf to __attribute__((format(scanf,...)
2012-03-23 16:58:36 -07:00
cpuset: mm: reduce large amounts of memory barrier related damage v3
2012-03-21 17:54:59 -07:00
crc32: bolt on crc32c
2012-03-23 16:58:38 -07:00
vfs: d_alloc_root() gone
2012-03-20 21:29:37 -04:00
dccp: fix bug in sequence number validation during connection setup
2012-03-03 09:02:52 -07:00
debugfs-related mode_t whack-a-mole
2012-03-20 21:29:53 -04:00
PM / devfreq: add relation of recommended frequency.
2012-03-17 21:51:34 +01:00
Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc
2012-03-21 18:55:10 -07:00
drivercore: Add driver probe deferral mechanism
2012-03-08 11:53:13 -08:00
ethtool, mdio, mii: Specify MDIO information fields in struct ethtool_cmd
2012-03-01 16:41:26 -05:00
udlfb: remove sysfs framebuffer device with USB .disconnect()
2012-03-15 13:35:22 +00:00
vfs: drop_file_write_access() made static
2012-03-20 21:29:32 -04:00
firewire: allow explicit flushing of iso packet completions
2012-03-18 22:15:39 +01:00
firewire: allow explicit flushing of iso packet completions
2012-03-18 22:15:39 +01:00
switch touch_atime to struct path
2012-03-20 21:29:41 -04:00
block: Fix NULL pointer dereference in sd_revalidate_disk
2012-03-02 10:38:33 +01:00
GFS2: FITRIM ioctl support
2012-02-28 17:10:21 +00:00
highmem: kill all __kmap_atomic()
2012-03-20 21:48:30 +08:00
thp: add HPAGE_PMD_* definitions for !CONFIG_TRANSPARENT_HUGEPAGE
2012-03-21 17:55:02 -07:00
hugetlbfs: fix alignment of huge page requests
2012-03-21 17:54:59 -07:00
Tools: hv: Support enumeration from all the pools
2012-03-16 13:36:04 -07:00
i2c: export bit-banging algo functions
2012-02-29 20:47:42 +01:00
ppp: Move ioctl definitions from if_ppp.h to new ppp-ioctl.h
2012-03-04 20:41:38 -05:00
if_vlan: Remove VLAN_ETH_ALEN define and the 1 use of it
2012-03-19 16:53:08 -04:00
arp: allow arp processing to honor per interface arp_accept sysctl
2012-03-16 23:00:20 -07:00
cpuset: mm: reduce large amounts of memory barrier related damage v3
2012-03-21 17:54:59 -07:00
Merge branch 'for-next' of github.com:rydberg/linux into next
2012-03-09 10:56:35 -08:00
ppp: Replace uses of <linux/if_ppp.h> with <linux/ppp-ioctl.h>
2012-03-04 20:41:38 -05:00
static keys: Inline the static_key_enabled() function
2012-02-28 20:01:08 +01:00
vt:tackle kbd_table
2012-03-08 10:50:35 -08:00
ppp: Move ioctl definitions from if_ppp.h to new ppp-ioctl.h
2012-03-04 20:41:38 -05:00
pagemap: export KPF_THP
2012-03-21 17:54:57 -07:00
include/ and checkpatch: prefer __scanf to __attribute__((format(scanf,...)
2012-03-23 16:58:36 -07:00
NFS client updates for Linux 3.4
2012-03-23 08:53:47 -07:00
vt:tackle kbd_table
2012-03-08 10:50:35 -08:00
kmsg_dump: don't run on non-error paths by default
2012-03-05 15:49:42 -08:00
leds-lm3530: support pwm input mode
2012-03-23 16:58:35 -07:00
drivers/leds/leds-lp5521.c: support led pattern data
2012-03-23 16:58:34 -07:00
[SCSI] libsas: async ata scanning
2012-02-29 15:35:41 -06:00
backlight: new backlight driver for LP855x devices
2012-03-23 16:58:33 -07:00
magic.h: move some FS magic numbers into magic.h
2012-03-23 16:58:31 -07:00
math: Introduce div64_long
2012-03-15 21:41:34 +01:00
mdio.h: Include linux/types.h
2012-03-03 15:04:45 -05:00
memcg: fix performance of mem_cgroup_begin_update_page_stat()
2012-03-21 17:55:02 -07:00
mm: replace PAGE_MIGRATION with IS_ENABLED(CONFIG_MIGRATION)
2012-03-21 17:54:57 -07:00
Merge branch 'x86-mce-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
2012-03-22 09:42:04 -07:00
vmscan: only defer compaction for failed order and higher
2012-03-21 17:54:56 -07:00
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
2012-03-20 21:04:47 -07:00
NFC: Add device powered netlink attribute
2012-03-06 15:16:19 -05:00
NFSv4: Simplify the struct nfs4_stateid
2012-03-06 10:32:47 -05:00
NFS: Fix more NFS debug related build warnings
2012-03-21 09:31:44 -04:00
NFS: Request fh_expire_type attribute in "server caps" operation
2012-03-02 17:18:10 -05:00
NFS: Undo changes to idmap.h
2012-03-05 15:26:47 -05:00
NFSv4.1: Clean ups and bugfixes for the pNFS read/writeback/commit code
2012-03-17 11:09:33 -04:00
NFS: Remove nfs4_setup_sequence from generic rename code
2012-03-21 09:31:46 -04:00
cfg80211: Add background scan period attribute.
2012-03-12 14:19:34 -04:00
nmi watchdog: do not use cpp symbol in Kconfig
2012-03-23 16:58:31 -07:00
Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc
2012-03-21 18:55:10 -07:00
dt: fix twl4030 for non-dt compile on x86
2012-03-05 08:09:09 -07:00
mm, oom: force oom kill on sysrq+f
2012-03-21 17:54:58 -07:00
padata: Fix race on sequence number wrap
2012-03-14 17:25:56 +08:00
thp: allow a hwpoisoned head page to be put back to LRU
2012-03-21 17:54:58 -07:00
memcg: remove PCG_FILE_MAPPED
2012-03-21 17:55:01 -07:00
Features:
2012-03-22 20:16:14 -07:00
tg3: Recode PCI MRRS adjustment as a PCI quirk
2012-03-04 20:54:01 -05:00
percpu: fix __this_cpu_{sub,inc,dec}_return() definition
2012-03-04 09:34:15 -08:00
perf: Add ABI reference sizes
2012-03-09 08:26:05 +01:00
magic.h: move some FS magic numbers into magic.h
2012-03-23 16:58:31 -07:00
Merge branch 'pm-qos'
2012-03-16 21:49:24 +01:00
PM / Domains: Introduce "always on" device flag
2012-03-16 21:44:59 +01:00
PM / QoS: Make it possible to expose PM QoS latency constraints
2012-03-13 22:37:14 +01:00
PM / Sleep: Add more wakeup source initialization routines
2012-03-04 23:08:46 +01:00
poll: add poll_requested_events() and poll_does_not_wait() functions
2012-03-23 16:58:38 -07:00
ppp: Change copyright notices from ANU to me
2012-03-04 20:41:38 -05:00
ppp: Move ioctl definitions from if_ppp.h to new ppp-ioctl.h
2012-03-04 20:41:38 -05:00
ppp: Change copyright notices from ANU to me
2012-03-04 20:41:38 -05:00
prctl: add PR_{SET,GET}_CHILD_SUBREAPER to allow simple process supervision
2012-03-23 16:58:32 -07:00
sched/rt: Document scheduler related skip-resched-check sites
2012-03-01 10:28:04 +01:00
driver core merge for 3.4-rc1
2012-03-20 11:16:20 -07:00
fs: initial qnx6fs addition
2012-03-20 21:29:38 -04:00
consolidate WARN_...ONCE() static variables
2012-03-23 16:58:31 -07:00
Merge remote-tracking branch 'regmap/topic/bulk' into regmap-next
2012-03-14 13:15:48 +00:00
regset: Return -EFAULT, not -EIO, on host-side memory fault
2012-03-02 11:38:15 -08:00
move private bits of reiserfs_fs.h to fs/reiserfs/reiserfs.h
2012-03-20 21:29:43 -04:00
take private bits of reiserfs_xattr.h to fs/reiserfs/xattr.h
2012-03-20 21:29:42 -04:00
rmap: remove __anon_vma_link() declaration
2012-03-21 17:54:57 -07:00
prctl: add PR_{SET,GET}_CHILD_SUBREAPER to allow simple process supervision
2012-03-23 16:58:32 -07:00
Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security
2012-03-21 13:25:04 -07:00
TTY: serial, simplify ASYNC_USR_MASK
2012-03-08 11:38:50 -08:00
serial: introduce generic port in/out helpers
2012-03-09 12:47:56 -08:00
net: update the usage of CHECKSUM_UNNECESSARY
2012-03-19 17:37:35 -04:00
tcp: reduce out_of_order memory use
2012-03-19 16:53:08 -04:00
net: get rid of some pointless casts to sockaddr
2012-03-11 19:11:22 -07:00
mm: drain percpu lru add/rotate page-vectors on cpu hot-unplug
2012-03-21 17:54:58 -07:00
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
2012-03-01 17:57:40 -05:00
constify path argument of trace_seq_path()
2012-03-20 21:29:40 -04:00
TTY: tty_driver, document tty->ops->shutdown limitation
2012-03-08 11:38:51 -08:00
USB: dynamically allocate usb_device children pointers instead of using a fix array
2012-03-13 14:24:07 -07:00
vt:tackle kbd_table
2012-03-08 10:50:35 -08:00
sched/wait: Add __wake_up_all_locked() API
2012-03-01 10:28:04 +01:00
Block: use a freezable workqueue for disk-event polling
2012-03-02 10:51:00 +01:00
writeback: fix typo in the writeback_control comment
2012-03-07 16:08:46 +01:00
