diff options
Diffstat (limited to 'Documentation/userspace-api')
| -rw-r--r-- | Documentation/userspace-api/futex2.rst | 86 | ||||
| -rw-r--r-- | Documentation/userspace-api/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/userspace-api/ioctl/cdrom.rst | 113 | ||||
| -rw-r--r-- | Documentation/userspace-api/ioctl/ioctl-number.rst | 1 | ||||
| -rw-r--r-- | Documentation/userspace-api/vduse.rst | 2 |
5 files changed, 147 insertions, 56 deletions
diff --git a/Documentation/userspace-api/futex2.rst b/Documentation/userspace-api/futex2.rst new file mode 100644 index 000000000000..9693f47a7e62 --- /dev/null +++ b/Documentation/userspace-api/futex2.rst @@ -0,0 +1,86 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====== +futex2 +====== + +:Author: André Almeida <andrealmeid@collabora.com> + +futex, or fast user mutex, is a set of syscalls to allow userspace to create +performant synchronization mechanisms, such as mutexes, semaphores and +conditional variables in userspace. C standard libraries, like glibc, uses it +as a means to implement more high level interfaces like pthreads. + +futex2 is a followup version of the initial futex syscall, designed to overcome +limitations of the original interface. + +User API +======== + +``futex_waitv()`` +----------------- + +Wait on an array of futexes, wake on any:: + + futex_waitv(struct futex_waitv *waiters, unsigned int nr_futexes, + unsigned int flags, struct timespec *timeout, clockid_t clockid) + + struct futex_waitv { + __u64 val; + __u64 uaddr; + __u32 flags; + __u32 __reserved; + }; + +Userspace sets an array of struct futex_waitv (up to a max of 128 entries), +using ``uaddr`` for the address to wait for, ``val`` for the expected value +and ``flags`` to specify the type (e.g. private) and size of futex. +``__reserved`` needs to be 0, but it can be used for future extension. The +pointer for the first item of the array is passed as ``waiters``. An invalid +address for ``waiters`` or for any ``uaddr`` returns ``-EFAULT``. + +If userspace has 32-bit pointers, it should do a explicit cast to make sure +the upper bits are zeroed. ``uintptr_t`` does the tricky and it works for +both 32/64-bit pointers. + +``nr_futexes`` specifies the size of the array. Numbers out of [1, 128] +interval will make the syscall return ``-EINVAL``. + +The ``flags`` argument of the syscall needs to be 0, but it can be used for +future extension. + +For each entry in ``waiters`` array, the current value at ``uaddr`` is compared +to ``val``. If it's different, the syscall undo all the work done so far and +return ``-EAGAIN``. If all tests and verifications succeeds, syscall waits until +one of the following happens: + +- The timeout expires, returning ``-ETIMEOUT``. +- A signal was sent to the sleeping task, returning ``-ERESTARTSYS``. +- Some futex at the list was woken, returning the index of some waked futex. + +An example of how to use the interface can be found at ``tools/testing/selftests/futex/functional/futex_waitv.c``. + +Timeout +------- + +``struct timespec *timeout`` argument is an optional argument that points to an +absolute timeout. You need to specify the type of clock being used at +``clockid`` argument. ``CLOCK_MONOTONIC`` and ``CLOCK_REALTIME`` are supported. +This syscall accepts only 64bit timespec structs. + +Types of futex +-------------- + +A futex can be either private or shared. Private is used for processes that +shares the same memory space and the virtual address of the futex will be the +same for all processes. This allows for optimizations in the kernel. To use +private futexes, it's necessary to specify ``FUTEX_PRIVATE_FLAG`` in the futex +flag. For processes that doesn't share the same memory space and therefore can +have different virtual addresses for the same futex (using, for instance, a +file-backed shared memory) requires different internal mechanisms to be get +properly enqueued. This is the default behavior, and it works with both private +and shared futexes. + +Futexes can be of different sizes: 8, 16, 32 or 64 bits. Currently, the only +supported one is 32 bit sized futex, and it need to be specified using +``FUTEX_32`` flag. diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index c432be070f67..a61eac0c73f8 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -28,6 +28,7 @@ place where this information is gathered. media/index sysfs-platform_profile vduse + futex2 .. only:: subproject and html diff --git a/Documentation/userspace-api/ioctl/cdrom.rst b/Documentation/userspace-api/ioctl/cdrom.rst index 3b4c0506de46..682948fc88a3 100644 --- a/Documentation/userspace-api/ioctl/cdrom.rst +++ b/Documentation/userspace-api/ioctl/cdrom.rst @@ -13,61 +13,64 @@ in drivers/cdrom/cdrom.c and drivers/block/scsi_ioctl.c ioctl values are listed in <linux/cdrom.h>. As of this writing, they are as follows: - ====================== =============================================== - CDROMPAUSE Pause Audio Operation - CDROMRESUME Resume paused Audio Operation - CDROMPLAYMSF Play Audio MSF (struct cdrom_msf) - CDROMPLAYTRKIND Play Audio Track/index (struct cdrom_ti) - CDROMREADTOCHDR Read TOC header (struct cdrom_tochdr) - CDROMREADTOCENTRY Read TOC entry (struct cdrom_tocentry) - CDROMSTOP Stop the cdrom drive - CDROMSTART Start the cdrom drive - CDROMEJECT Ejects the cdrom media - CDROMVOLCTRL Control output volume (struct cdrom_volctrl) - CDROMSUBCHNL Read subchannel data (struct cdrom_subchnl) - CDROMREADMODE2 Read CDROM mode 2 data (2336 Bytes) - (struct cdrom_read) - CDROMREADMODE1 Read CDROM mode 1 data (2048 Bytes) - (struct cdrom_read) - CDROMREADAUDIO (struct cdrom_read_audio) - CDROMEJECT_SW enable(1)/disable(0) auto-ejecting - CDROMMULTISESSION Obtain the start-of-last-session - address of multi session disks - (struct cdrom_multisession) - CDROM_GET_MCN Obtain the "Universal Product Code" - if available (struct cdrom_mcn) - CDROM_GET_UPC Deprecated, use CDROM_GET_MCN instead. - CDROMRESET hard-reset the drive - CDROMVOLREAD Get the drive's volume setting - (struct cdrom_volctrl) - CDROMREADRAW read data in raw mode (2352 Bytes) - (struct cdrom_read) - CDROMREADCOOKED read data in cooked mode - CDROMSEEK seek msf address - CDROMPLAYBLK scsi-cd only, (struct cdrom_blk) - CDROMREADALL read all 2646 bytes - CDROMGETSPINDOWN return 4-bit spindown value - CDROMSETSPINDOWN set 4-bit spindown value - CDROMCLOSETRAY pendant of CDROMEJECT - CDROM_SET_OPTIONS Set behavior options - CDROM_CLEAR_OPTIONS Clear behavior options - CDROM_SELECT_SPEED Set the CD-ROM speed - CDROM_SELECT_DISC Select disc (for juke-boxes) - CDROM_MEDIA_CHANGED Check is media changed - CDROM_DRIVE_STATUS Get tray position, etc. - CDROM_DISC_STATUS Get disc type, etc. - CDROM_CHANGER_NSLOTS Get number of slots - CDROM_LOCKDOOR lock or unlock door - CDROM_DEBUG Turn debug messages on/off - CDROM_GET_CAPABILITY get capabilities - CDROMAUDIOBUFSIZ set the audio buffer size - DVD_READ_STRUCT Read structure - DVD_WRITE_STRUCT Write structure - DVD_AUTH Authentication - CDROM_SEND_PACKET send a packet to the drive - CDROM_NEXT_WRITABLE get next writable block - CDROM_LAST_WRITTEN get last block written on disc - ====================== =============================================== + ======================== =============================================== + CDROMPAUSE Pause Audio Operation + CDROMRESUME Resume paused Audio Operation + CDROMPLAYMSF Play Audio MSF (struct cdrom_msf) + CDROMPLAYTRKIND Play Audio Track/index (struct cdrom_ti) + CDROMREADTOCHDR Read TOC header (struct cdrom_tochdr) + CDROMREADTOCENTRY Read TOC entry (struct cdrom_tocentry) + CDROMSTOP Stop the cdrom drive + CDROMSTART Start the cdrom drive + CDROMEJECT Ejects the cdrom media + CDROMVOLCTRL Control output volume (struct cdrom_volctrl) + CDROMSUBCHNL Read subchannel data (struct cdrom_subchnl) + CDROMREADMODE2 Read CDROM mode 2 data (2336 Bytes) + (struct cdrom_read) + CDROMREADMODE1 Read CDROM mode 1 data (2048 Bytes) + (struct cdrom_read) + CDROMREADAUDIO (struct cdrom_read_audio) + CDROMEJECT_SW enable(1)/disable(0) auto-ejecting + CDROMMULTISESSION Obtain the start-of-last-session + address of multi session disks + (struct cdrom_multisession) + CDROM_GET_MCN Obtain the "Universal Product Code" + if available (struct cdrom_mcn) + CDROM_GET_UPC Deprecated, use CDROM_GET_MCN instead. + CDROMRESET hard-reset the drive + CDROMVOLREAD Get the drive's volume setting + (struct cdrom_volctrl) + CDROMREADRAW read data in raw mode (2352 Bytes) + (struct cdrom_read) + CDROMREADCOOKED read data in cooked mode + CDROMSEEK seek msf address + CDROMPLAYBLK scsi-cd only, (struct cdrom_blk) + CDROMREADALL read all 2646 bytes + CDROMGETSPINDOWN return 4-bit spindown value + CDROMSETSPINDOWN set 4-bit spindown value + CDROMCLOSETRAY pendant of CDROMEJECT + CDROM_SET_OPTIONS Set behavior options + CDROM_CLEAR_OPTIONS Clear behavior options + CDROM_SELECT_SPEED Set the CD-ROM speed + CDROM_SELECT_DISC Select disc (for juke-boxes) + CDROM_MEDIA_CHANGED Check is media changed + CDROM_TIMED_MEDIA_CHANGE Check if media changed + since given time + (struct cdrom_timed_media_change_info) + CDROM_DRIVE_STATUS Get tray position, etc. + CDROM_DISC_STATUS Get disc type, etc. + CDROM_CHANGER_NSLOTS Get number of slots + CDROM_LOCKDOOR lock or unlock door + CDROM_DEBUG Turn debug messages on/off + CDROM_GET_CAPABILITY get capabilities + CDROMAUDIOBUFSIZ set the audio buffer size + DVD_READ_STRUCT Read structure + DVD_WRITE_STRUCT Write structure + DVD_AUTH Authentication + CDROM_SEND_PACKET send a packet to the drive + CDROM_NEXT_WRITABLE get next writable block + CDROM_LAST_WRITTEN get last block written on disc + ======================== =============================================== The information that follows was determined from reading kernel source diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst index 2e8134059c87..6655d929a351 100644 --- a/Documentation/userspace-api/ioctl/ioctl-number.rst +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst @@ -104,6 +104,7 @@ Code Seq# Include File Comments '8' all SNP8023 advanced NIC card <mailto:mcr@solidum.com> ';' 64-7F linux/vfio.h +'=' 00-3f uapi/linux/ptp_clock.h <mailto:richardcochran@gmail.com> '@' 00-0F linux/radeonfb.h conflict! '@' 00-0F drivers/video/aty/aty128fb.c conflict! 'A' 00-1F linux/apm_bios.h conflict! diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst index 42ef59ea5314..bdb880e01132 100644 --- a/Documentation/userspace-api/vduse.rst +++ b/Documentation/userspace-api/vduse.rst @@ -18,7 +18,7 @@ types can be added after the security issue of corresponding device driver is clarified or fixed in the future. Create/Destroy VDUSE devices ------------------------- +---------------------------- VDUSE devices are created as follows: |