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52 lines
2 KiB
Markdown
52 lines
2 KiB
Markdown
## Name
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sys - SerenityOS SysFS
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## Description
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The kernel can expose system (kernel, firmware and hardware) related information in /sys.
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### `bus` directory
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This directory include a subdirectory for each discovered and registered bus in the system.
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Possible busses to be exposed in this directory are:
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1. The `pci` subdirectory that includes all discovered PCI devices as subdirectories.
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The subdirectories of the PCI devices include files with basic information on the devices.
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2. The `usb` subdirectory that includes all discovered USB devices as files.
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The files of the USB devices export basic information on the devices.
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### `dev` directory
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This directory include two subdirectories - `block` and `char`, each for block
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and character devices respectively. The files in these subdirectories are not
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device files, but merely a file with filename layout of "major:minor", to aid
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userspace in generating the appropriate device files.
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### `firmware` directory
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This directory include two subdirectories - `acpi` and `bios`.
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The `bios` subdirectory maintains files of the exposed SMBIOS blobs, if present
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by the firmware.
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The `acpi` subdirectory maintains files of the exposed ACPI tables, if present
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by the firmware.
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A file called `power_state` is responsible for power state switching.
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#### `power_state`
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This file only responds to write requests on it. A written value of `1` results
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in system reboot. A written value of `2` results in system shutdown.
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### Consistency and stability of data across multiple read operations
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When opening a data node, the kernel generates the required data so it's prepared
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for read operation when requested to. However, in order to ensure that multiple reads
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will not create a corrupted data from that data node, a read operation alone will
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not inquire the kernel to refresh the data.
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To keep data output being refreshed, the userland has to re-open the data node with a
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new file descriptor, or to perform the `lseek` syscall on the open file descriptor to
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reset the the offset to 0.
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## See also
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* [`mount`(2))](../man2/mount.md).
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