ABI removed symbols¶
Symbols under /sys/bus¶
/sys/bus/nd/devices/regionX/nfit/ecc_unit_size |
Defined on file sysfs-bus-nfit
(RO) Size of a write request to a DIMM that will not incur a read-modify-write cycle at the memory controller.
When the nfit driver initializes it runs an ARS (Address Range Scrub) operation across every pmem range. Part of that process involves determining the ARS capabilities of a given address range. One of the capabilities that is reported is the ‘Clear Uncorrectable Error Range Length Unit Size’ (see: ACPI 6.2 section 9.20.7.4 Function Index 1 - Query ARS Capabilities). This property indicates the boundary at which the NVDIMM may need to perform read-modify-write cycles to maintain ECC (Error Correcting Code) blocks.
Symbols under /sys/class¶
/sys/class/cxl/<afu>/afu_err_buf |
Defined on file sysfs-class-cxl
read only AFU Error Buffer contents. The contents of this file are application specific and depends on the AFU being used. Applications interacting with the AFU can use this attribute to know about the current error condition and take appropriate action like logging the event etc.
/sys/class/cxl/<afu>/api_version |
Defined on file sysfs-class-cxl
read only Decimal value of the current version of the kernel/user API.
/sys/class/cxl/<afu>/api_version_compatible |
Defined on file sysfs-class-cxl
read only Decimal value of the lowest version of the userspace API this kernel supports.
- Users:
https://github.com/ibm-capi/libcxl
AFU configuration records (eg. /sys/class/cxl/afu0.0/cr0):
An AFU may optionally export one or more PCIe like configuration records, known as AFU configuration records, which will show up here (if present).
/sys/class/cxl/<afu>/cr<config num>/class |
Defined on file sysfs-class-cxl
read only Hexadecimal value of the class code found in this AFU configuration record.
/sys/class/cxl/<afu>/cr<config num>/config |
Defined on file sysfs-class-cxl
read only This binary file provides raw access to the AFU configuration record. The format is expected to match the either the standard or extended configuration space defined by the PCIe specification.
- Users:
https://github.com/ibm-capi/libcxl
Master contexts (eg. /sys/class/cxl/afu0.0m)
/sys/class/cxl/<afu>/cr<config num>/device |
Defined on file sysfs-class-cxl
read only Hexadecimal value of the device ID found in this AFU configuration record.
/sys/class/cxl/<afu>/cr<config num>/vendor |
Defined on file sysfs-class-cxl
read only Hexadecimal value of the vendor ID found in this AFU configuration record.
/sys/class/cxl/<afu>/irqs_max |
Defined on file sysfs-class-cxl
read/write Decimal value of maximum number of interrupts that can be requested by userspace. The default on probe is the maximum that hardware can support (eg. 2037). Write values will limit userspace applications to that many userspace interrupts. Must be >= irqs_min.
/sys/class/cxl/<afu>/irqs_min |
Defined on file sysfs-class-cxl
read only Decimal value of the minimum number of interrupts that userspace must request on a CXL_START_WORK ioctl. Userspace may omit the num_interrupts field in the START_WORK IOCTL to get this minimum automatically.
/sys/class/cxl/<afu>/mmio_size |
Defined on file sysfs-class-cxl
read only Decimal value of the size of the MMIO space that may be mmapped by userspace.
/sys/class/cxl/<afu>/mode |
Defined on file sysfs-class-cxl
read/write The current mode the AFU is using. Will be one of the modes given in modes_supported. Writing will change the mode provided that no user contexts are attached.
/sys/class/cxl/<afu>/modes_supported |
Defined on file sysfs-class-cxl
read only List of the modes this AFU supports. One per line. Valid entries are: “dedicated_process” and “afu_directed”
/sys/class/cxl/<afu>/prefault_mode |
Defined on file sysfs-class-cxl
read/write Set the mode for prefaulting in segments into the segment table when performing the START_WORK ioctl. Only applicable when running under hashed page table mmu. Possible values:
none |
No prefaulting (default) |
work_element_descriptor |
Treat the work element descriptor as an effective address and prefault what it points to. |
all |
all segments process calling START_WORK maps. |
/sys/class/cxl/<afu>/reset |
Defined on file sysfs-class-cxl
write only Writing 1 here will reset the AFU provided there are not contexts active on the AFU.
/sys/class/cxl/<afu>m/mmio_size |
Defined on file sysfs-class-cxl
read only Decimal value of the size of the MMIO space that may be mmapped by userspace. This includes all slave contexts space also.
/sys/class/cxl/<afu>m/pp_mmio_len |
Defined on file sysfs-class-cxl
read only Decimal value of the Per Process MMIO space length.
/sys/class/cxl/<afu>m/pp_mmio_off |
Defined on file sysfs-class-cxl
read only (not in a guest) Decimal value of the Per Process MMIO space offset.
- Users:
https://github.com/ibm-capi/libcxl
Card info (eg. /sys/class/cxl/card0)
/sys/class/cxl/<card>/base_image |
Defined on file sysfs-class-cxl
read only (not in a guest) Identifies the revision level of the base image for devices that support loadable PSLs. For FPGAs this field identifies the image contained in the on-adapter flash which is loaded during the initial program load.
/sys/class/cxl/<card>/caia_version |
Defined on file sysfs-class-cxl
read only Identifies the CAIA Version the card implements.
/sys/class/cxl/<card>/image_loaded |
Defined on file sysfs-class-cxl
read only (not in a guest) Will return “user” or “factory” depending on the image loaded onto the card.
/sys/class/cxl/<card>/load_image_on_perst |
Defined on file sysfs-class-cxl
read/write (not in a guest) Valid entries are “none”, “user”, and “factory”. “none” means PERST will not cause image to be loaded to the card. A power cycle is required to load the image. “none” could be useful for debugging because the trace arrays are preserved.
“user” and “factory” means PERST will cause either the user or user or factory image to be loaded. Default is to reload on PERST whichever image the card has loaded.
/sys/class/cxl/<card>/perst_reloads_same_image |
Defined on file sysfs-class-cxl
read/write (not in a guest) Trust that when an image is reloaded via PERST, it will not have changed.
0 |
don’t trust, the image may be different (default) |
1 |
trust that the image will not change. |
/sys/class/cxl/<card>/psl_revision |
Defined on file sysfs-class-cxl
read only Identifies the revision level of the PSL.
/sys/class/cxl/<card>/psl_timebase_synced |
Defined on file sysfs-class-cxl
read only Returns 1 if the psl timebase register is synchronized with the core timebase register, 0 otherwise.
/sys/class/cxl/<card>/reset |
Defined on file sysfs-class-cxl
write only Writing 1 will issue a PERST to card provided there are no contexts active on any one of the card AFUs. This may cause the card to reload the FPGA depending on load_image_on_perst. Writing -1 will do a force PERST irrespective of any active contexts on the card AFUs.
/sys/class/cxl/<card>/tunneled_ops_supported |
Defined on file sysfs-class-cxl
read only Returns 1 if tunneled operations are supported in capi mode, 0 otherwise.
/sys/class/rfkill/rfkill[0-9]+/claim |
Defined on file sysfs-class-rfkill
This file was deprecated because there no longer was a way to claim just control over a single rfkill instance. This file was scheduled to be removed in 2012, and was removed in 2016. Values: 0: Kernel handles events
Symbols under /sys/devices¶
/sys/devices/system/machinecheck/machinecheckX/tolerant |
Defined on file sysfs-mce
Unused and obsolete after the advent of recoverable machine checks (see last sentence below) and those are present since 2010 (Nehalem).
Original description:
The entries appear for each CPU, but they are truly shared between all CPUs.
Tolerance level. When a machine check exception occurs for a non corrected machine check the kernel can take different actions.
Since machine check exceptions can happen any time it is sometimes risky for the kernel to kill a process because it defies normal kernel locking rules. The tolerance level configures how hard the kernel tries to recover even at some risk of deadlock. Higher tolerant values trade potentially better uptime with the risk of a crash or even corruption (for tolerant >= 3).
0 |
always panic on uncorrected errors, log corrected errors |
1 |
panic or SIGBUS on uncorrected errors, log corrected errors |
2 |
SIGBUS or log uncorrected errors, log corrected errors |
3 |
never panic or SIGBUS, log all errors (for testing only) |
Default: 1
Note this only makes a difference if the CPU allows recovery from a machine check exception. Current x86 CPUs generally do not.
Symbols under /sys/firmware¶
/sys/firmware/efi/vars |
Defined on file sysfs-firmware-efi-vars
This directory exposed interfaces for interacting with EFI variables. For more information on EFI variables, see ‘Variable Services’ in the UEFI specification (section 7.2 in specification version 2.3 Errata D).
The ‘efivars’ sysfs interface was removed in March of 2023, after being considered deprecated no later than September of 2020. Its functionality has been replaced by the ‘efivarfs’ filesystem.
Symbols under /sys/fs¶
/sys/fs/selinux/checkreqprot |
Defined on file sysfs-selinux-checkreqprot
REMOVAL UPDATE: The SELinux checkreqprot functionality was removed in March 2023, the original deprecation notice is shown below.
The selinuxfs “checkreqprot” node allows SELinux to be configured to check the protection requested by userspace for mmap/mprotect calls instead of the actual protection applied by the kernel. This was a compatibility mechanism for legacy userspace and for the READ_IMPLIES_EXEC personality flag. However, if set to 1, it weakens security by allowing mappings to be made executable without authorization by policy. The default value of checkreqprot at boot was changed starting in Linux v4.4 to 0 (i.e. check the actual protection), and Android and Linux distributions have been explicitly writing a “0” to /sys/fs/selinux/checkreqprot during initialization for some time. Support for setting checkreqprot to 1 will be removed no sooner than June 2021, at which point the kernel will always cease using checkreqprot internally and will always check the actual protections being applied upon mmap/mprotect calls. The checkreqprot selinuxfs node will remain for backward compatibility but will discard writes of the “0” value and will reject writes of the “1” value when this mechanism is removed.
/sys/fs/selinux/disable |
Defined on file sysfs-selinux-disable
REMOVAL UPDATE: The SELinux runtime disable functionality was removed in March 2023, the original deprecation notice is shown below.
The selinuxfs “disable” node allows SELinux to be disabled at runtime prior to a policy being loaded into the kernel. If disabled via this mechanism, SELinux will remain disabled until the system is rebooted.
The preferred method of disabling SELinux is via the “selinux=0” boot parameter, but the selinuxfs “disable” node was created to make it easier for systems with primitive bootloaders that did not allow for easy modification of the kernel command line. Unfortunately, allowing for SELinux to be disabled at runtime makes it difficult to secure the kernel’s LSM hooks using the “__ro_after_init” feature.
Thankfully, the need for the SELinux runtime disable appears to be gone, the default Kconfig configuration disables this selinuxfs node, and only one of the major distributions, Fedora, supports disabling SELinux at runtime. Fedora is in the process of removing the selinuxfs “disable” node and once that is complete we will start the slow process of removing this code from the kernel.
More information on /sys/fs/selinux/disable can be found under the CONFIG_SECURITY_SELINUX_DISABLE Kconfig option.
Symbols under /sys/kernel¶
/sys/kernel/fadump_release_opalcore |
Defined on file sysfs-kernel-fadump_release_opalcore
write only The sysfs file is available when the system is booted to collect the dump on OPAL based machine. It used to release the memory used to collect the opalcore.
/sys/kernel/uids/<uid>/cpu_shares |
Defined on file sysfs-kernel-uids
The /sys/kernel/uids/<uid>/cpu_shares tunable is used to set the cpu bandwidth a user is allowed. This is a proportional value. What that means is that if there are two users logged in, each with an equal number of shares, then they will get equal CPU bandwidth. Another example would be, if User A has shares = 1024 and user B has shares = 2048, User B will get twice the CPU bandwidth user A will. For more details refer CFS Scheduler
Symbols under /sys/o2cb¶
/sys/o2cb symlink |
Defined on file o2cb
This is a symlink: /sys/o2cb to /sys/fs/o2cb. The symlink is removed when new versions of ocfs2-tools which know to look in /sys/fs/o2cb are sufficiently prevalent. Don’t code new software to look here, it should try /sys/fs/o2cb instead.
- Users:
ocfs2-tools. It’s sufficient to mail proposed changes to ocfs2-devel@lists.linux.dev.
devfs¶
devfs |
Defined on file devfs
devfs has been unmaintained for a number of years, has unfixable races, contains a naming policy within the kernel that is against the LSB, and can be replaced by using udev.
The files fs/devfs/, include/linux/devfs_fs.h were removed, along with the assorted devfs function calls throughout the kernel tree.
Symbols under dv1394¶
dv1394 (a.k.a. "OHCI-DV I/O support" for FireWire) |
Defined on file dv1394
/dev/dv1394/* were character device files, one for each FireWire controller and for NTSC and PAL respectively, from which DV data could be received by read() or transmitted by write(). A few ioctl()s allowed limited control. This special-purpose interface has been superseded by libraw1394 + libiec61883 which are functionally equivalent, support HDV, and transparently work on top of the newer firewire kernel drivers.
- Users:
ffmpeg/libavformat (if configured for DV1394)
ip_queue¶
ip_queue |
Defined on file ip_queue
ip_queue has been replaced by nfnetlink_queue which provides more advanced queueing mechanism to user-space. The ip_queue module was already announced to become obsolete years ago.
Symbols under raw1394¶
raw1394 (a.k.a. "Raw IEEE1394 I/O support" for FireWire) |
Defined on file raw1394
/dev/raw1394 was a character device file that allowed low-level access to FireWire buses. Its major drawbacks were its inability to implement sensible device security policies, and its low level of abstraction that required userspace clients to duplicate much of the kernel’s ieee1394 core functionality.
Replaced by /dev/fw*, i.e. the <linux/firewire-cdev.h> ABI of firewire-core.
- Users:
libraw1394 (works with firewire-cdev too, transparent to library ABI users)
tcp_dma_copybreak sysctl¶
tcp_dma_copybreak sysctl |
Defined on file net_dma
Formerly the lower limit, in bytes, of the size of socket reads that will be offloaded to a DMA copy engine. Removed due to coherency issues of the cpu potentially touching the buffers while dma is in flight.
video1394 (a.k.a. “OHCI-1394 Video support” for FireWire)¶
video1394 (a.k.a. "OHCI-1394 Video support" for FireWire) |
Defined on file video1394
/dev/video1394/* were character device files, one for each FireWire controller, which were used for isochronous I/O. It was added as an alternative to raw1394’s isochronous I/O functionality which had performance issues in its first generation. Any video1394 user had to use raw1394 + libraw1394 too because video1394 did not provide asynchronous I/O for device discovery and configuration.
Replaced by /dev/fw*, i.e. the <linux/firewire-cdev.h> ABI of firewire-core.
- Users:
libdc1394 (works with firewire-cdev too, transparent to library ABI users)