Name

sys - SerenityOS SysFS

Description

The kernel can expose system (kernel, firmware and hardware) related information in /sys.

bus directory

This directory include a subdirectory for each discovered and registered bus in the system.

Possible busses to be exposed in this directory are:

1. The pci subdirectory that includes all discovered PCI devices as subdirectories. The subdirectories of the PCI devices include files with basic information on the devices.
2. The usb subdirectory that includes all discovered USB devices as files. The files of the USB devices export basic information on the devices.

dev directory

This directory include two subdirectories - block and char, each for block and character devices respectively. The files in these subdirectories are not device files, but merely a file with filename layout of "major:minor", to aid userspace in generating the appropriate device files.

firmware directory

This directory include two subdirectories - acpi and bios. The bios subdirectory maintains files of the exposed SMBIOS blobs, if present by the firmware. The acpi subdirectory maintains files of the exposed ACPI tables, if present by the firmware. A file called power_state is responsible for power state switching.

power_state

This file only responds to write requests on it. A written value of 1 results in system reboot. A written value of 2 results in system shutdown.

Consistency and stability of data across multiple read operations

When opening a data node, the kernel generates the required data so it's prepared for read operation when requested to. However, in order to ensure that multiple reads will not create a corrupted data from that data node, a read operation alone will not inquire the kernel to refresh the data. To keep data output being refreshed, the userland has to re-open the data node with a new file descriptor, or to perform the lseek syscall on the open file descriptor to reset the the offset to 0.

See also

• mount(2)).