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David Howells 8cefc107ca pipe: Use head and tail pointers for the ring, not cursor and length 
Convert pipes to use head and tail pointers for the buffer ring rather than
pointer and length as the latter requires two atomic ops to update (or a
combined op) whereas the former only requires one.

 (1) The head pointer is the point at which production occurs and points to
     the slot in which the next buffer will be placed.  This is equivalent
     to pipe->curbuf + pipe->nrbufs.

     The head pointer belongs to the write-side.

 (2) The tail pointer is the point at which consumption occurs.  It points
     to the next slot to be consumed.  This is equivalent to pipe->curbuf.

     The tail pointer belongs to the read-side.

 (3) head and tail are allowed to run to UINT_MAX and wrap naturally.  They
     are only masked off when the array is being accessed, e.g.:

	pipe->bufs[head & mask]

     This means that it is not necessary to have a dead slot in the ring as
     head == tail isn't ambiguous.

 (4) The ring is empty if "head == tail".

     A helper, pipe_empty(), is provided for this.

 (5) The occupancy of the ring is "head - tail".

     A helper, pipe_occupancy(), is provided for this.

 (6) The number of free slots in the ring is "pipe->ring_size - occupancy".

     A helper, pipe_space_for_user() is provided to indicate how many slots
     userspace may use.

 (7) The ring is full if "head - tail >= pipe->ring_size".

     A helper, pipe_full(), is provided for this.

Signed-off-by: David Howells <dhowells@redhat.com>
2019-10-31 15:12:34 +00:00
..
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acpi Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
amba ARM updates for 5.4-rc1: 2019-09-22 09:39:09 -07:00
android
ata ata: libahci_platform: Add of_node_put() before loop exit 2019-09-19 12:21:44 -06:00
atm atm: he: clean up an indentation issue 2019-09-25 13:54:45 +02:00
auxdisplay It's a somewhat calmer cycle for docs this time, as the churn of the mass 2019-09-17 16:22:26 -07:00
base mm,thp: stats for file backed THP 2019-09-24 15:54:11 -07:00
bcma bcma: make arrays pwr_info_offset and sprom_sizes static const, shrinks object size 2019-09-13 16:44:49 +03:00
block for-linus-2019-10-03 2019-10-04 09:56:51 -07:00
bluetooth Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-15 14:17:27 +02:00
bus ARM: SoC fixes 2019-09-30 10:04:28 -07:00
cdrom
char pipe: Use head and tail pointers for the ring, not cursor and length 2019-10-31 15:12:34 +00:00
clk Fixes for omaps for v5.4-rc cycle 2019-10-03 09:15:19 -07:00
clocksource timer-of: don't use conditional expression with mixed 'void' types 2019-10-02 16:16:07 -07:00
connector
counter
cpufreq Power management updates for 5.4-rc1 2019-09-17 19:15:14 -07:00
cpuidle Power management updates for 5.4-rc1 2019-09-17 19:15:14 -07:00
crypto Merge branch 'akpm' (patches from Andrew) 2019-09-24 16:10:23 -07:00
dax
dca
devfreq
dio
dma Main MIPS changes for v5.4: 2019-09-22 09:30:30 -07:00
dma-buf
edac ARM updates for 5.4-rc1: 2019-09-22 09:39:09 -07:00
eisa
extcon chrome platform changes for v5.4 2019-09-19 14:14:28 -07:00
firewire
firmware ARM: SoC fixes 2019-09-30 10:04:28 -07:00
fpga Char/Misc driver patches for 5.4-rc1 2019-09-18 11:14:31 -07:00
fsi
gnss
gpio pwm: Changes for v5.4-rc1 2019-09-27 12:19:47 -07:00
gpu - Fix DP-MST crtc_mask 2019-10-04 16:31:06 +10:00
greybus
hid - First round of vmbus hibernation support from Dexuan Cui. 2019-09-24 12:36:31 -07:00
hsi HSI changes for the 5.4 series 2019-09-22 12:02:21 -07:00
hv - First round of vmbus hibernation support from Dexuan Cui. 2019-09-24 12:36:31 -07:00
hwmon ARM SCMI fixes for v5.4 2019-09-29 11:20:41 -07:00
hwspinlock
hwtracing Char/Misc driver patches for 5.4-rc1 2019-09-18 11:14:31 -07:00
i2c i2c: slave-eeprom: Add read only mode 2019-09-28 20:44:12 +02:00
i3c
ide
idle
iio chrome platform changes for v5.4 2019-09-19 14:14:28 -07:00
infiniband Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-28 17:47:33 -07:00
input chrome platform changes for v5.4 2019-09-19 14:14:28 -07:00
interconnect
iommu IOMMU Fixes for Linux v5.4-rc1 2019-09-29 10:00:14 -07:00
ipack
irqchip Main MIPS changes for v5.4: 2019-09-22 09:30:30 -07:00
isdn mISDN: enforce CAP_NET_RAW for raw sockets 2019-09-24 16:37:18 +02:00
leds leds: lm3532: Fix optional led-max-microamp prop error handling 2019-09-12 20:45:52 +02:00
lightnvm lightnvm: print error when target is not found 2019-09-05 13:17:01 -06:00
macintosh
mailbox mailbox: qcom-apcs: fix max_register value 2019-09-17 00:54:29 -05:00
mcb
md for-5.4/post-2019-09-24 2019-09-24 16:31:50 -07:00
media media/v4l2-core: untag user pointers in videobuf_dma_contig_user_get 2019-09-25 17:51:41 -07:00
memory
memstick ms_block: fix spelling mistake "randomally" -> "randomly" 2019-09-11 16:11:01 +02:00
message
mfd Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux-soc-thermal 2019-09-29 10:24:23 -07:00
misc Merge branch 'i2c/for-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2019-09-24 16:48:02 -07:00
mmc mmc: host: sdhci-pci: Add Genesys Logic GL975x support 2019-09-27 20:48:20 +02:00
mtd Main MIPS changes for v5.4: 2019-09-22 09:30:30 -07:00
mux
net net: qlogic: Fix memory leak in ql_alloc_large_buffers 2019-10-04 18:33:13 -07:00
nfc NFC: st95hf: clean up indentation issue 2019-09-27 20:31:18 +02:00
ntb NTB: fix IDT Kconfig typos/spellos 2019-09-23 17:20:40 -04:00
nubus
nvdimm libnvdimm fixes v5.4-rc1 2019-09-29 10:33:41 -07:00
nvme Merge branch 'nvme-5.4' of git://git.infradead.org/nvme into for-linus 2019-09-27 13:17:37 -06:00
nvmem Char/Misc driver patches for 5.4-rc1 2019-09-18 11:14:31 -07:00
of Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-28 17:47:33 -07:00
opp
oprofile
parisc dma-mapping updates for 5.4: 2019-09-19 13:27:23 -07:00
parport Char/Misc driver patches for 5.4-rc1 2019-09-18 11:14:31 -07:00
pci Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
pcmcia Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
perf
phy pci-v5.4-changes 2019-09-23 19:16:01 -07:00
pinctrl This is the bulk of pin control changes for the v5.4 kernel 2019-09-19 14:19:33 -07:00
platform platform-drivers-x86 for v5.4-2 2019-09-24 12:39:40 -07:00
pnp
power power supply and reset changes for the v5.4 series 2019-09-22 12:04:59 -07:00
powercap Power management updates for 5.4-rc1 2019-09-17 19:15:14 -07:00
pps
ps3
ptp ptp_qoriq: Initialize the registers' spinlock before calling ptp_qoriq_settime 2019-10-02 12:20:38 -04:00
pwm pwm: Changes for v5.4-rc1 2019-09-27 12:19:47 -07:00
rapidio
ras
regulator LED updates for 5.4-rc1 2019-09-17 18:40:42 -07:00
remoteproc remoteproc updates for v5.4 2019-09-22 10:55:08 -07:00
reset ARM: SoC fixes 2019-09-30 10:04:28 -07:00
rpmsg rpmsg: glink-smem: Name the edge based on parent remoteproc 2019-09-17 15:33:31 -07:00
rtc RTC for 5.4 2019-09-22 11:05:43 -07:00
s390 s390 updates for 5.4-rc2 2019-10-05 08:44:02 -07:00
sbus
scsi SCSI fixes on 20191004 2019-10-05 12:53:27 -07:00
sfi
sh
siox
slimbus
soc ARM: SoC driver updates for v5.4 2019-09-16 15:52:38 -07:00
soundwire soundwire updates for v5.4-rc1 2019-09-22 10:52:23 -07:00
spi LED updates for 5.4-rc1 2019-09-17 18:40:42 -07:00
spmi
ssb ssb: make array pwr_info_offset static const, makes object smaller 2019-09-13 17:23:18 +03:00
staging netfilter: drop bridge nf reset from nf_reset 2019-10-01 18:42:15 +02:00
target mm: introduce page_size() 2019-09-24 15:54:08 -07:00
tc
tee tee/shm: untag user pointers in tee_shm_register 2019-09-25 17:51:41 -07:00
thermal Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux-soc-thermal 2019-09-29 10:24:23 -07:00
thunderbolt
tty Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
uio Char/Misc driver patches for 5.4-rc1 2019-09-18 11:14:31 -07:00
usb Merge branch 'work.mount3' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-09-24 12:33:34 -07:00
vfio vfio/type1: untag user pointers in vaddr_get_pfn 2019-09-25 17:51:41 -07:00
vhost Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-15 14:17:27 +02:00
video video/logo: do not generate unneeded logo C files 2019-10-05 15:29:49 +09:00
virt
virtio virtio_ring: fix unmap of indirect descriptors 2019-09-09 10:43:15 -04:00
visorbus
vlynq
vme
w1
watchdog linux-watchdog 5.4-rc1 tag 2019-09-27 11:17:38 -07:00
xen xen: fixes and cleanups for 5.4-rc2 2019-10-04 11:13:09 -07:00
zorro
Kconfig Staging/IIO driver patches for 5.4-rc1 2019-09-18 11:05:34 -07:00
Makefile Staging/IIO driver patches for 5.4-rc1 2019-09-18 11:05:34 -07:00